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[Illustration:

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_Published by Bumpus & Griffin London, 1831._]




  THE

  ART OF GLASS-BLOWING,

  OR

  PLAIN INSTRUCTIONS

  FOR MAKING THE

  CHEMICAL AND PHILOSOPHICAL
  INSTRUMENTS

  WHICH ARE FORMED OF GLASS;

  SUCH AS

  BAROMETERS, THERMOMETERS, HYDROMETERS,

  _Hour-Glasses_, _Funnels_, _Syphons_,

  TUBE VESSELS FOR CHEMICAL EXPERIMENTS,

  TOYS FOR RECREATIVE PHILOSOPHY, &c.


  BY A FRENCH ARTIST.


  ILLUSTRATED BY ENGRAVINGS.

  LONDON:

  PUBLISHED BY BUMPUS AND GRIFFIN, 3, SKINNER-STREET;
  AND RICHARD GRIFFIN AND CO. GLASGOW:
  SOLD ALSO BY STILLIES, BROTHERS, EDINBURGH.

  1831.


W. WILSON, PRINTER, 57, SKINNER-STREET, LONDON.




THE POLYTECHNIC LIBRARY.


The design of the Publishers of the POLYTECHNIC LIBRARY is to produce
a Series of highly-instructive Works, which the Public may be tempted
to _buy_, because they will be cheap,--be induced to _read_, because
they will be brief,--be competent to _understand_, because they will
be clearly written,--and be able to _profit by_, because they will be
WORKS OF PRACTICAL UTILITY. Every volume, therefore, will contain _a
complete Treatise_ relating to one of the useful arts or sciences, or
the chemical or mechanical trades.


  JUST PUBLISHED, PRICE HALF-A-CROWN,
  VOL. I. OF THE POLYTECHNIC LIBRARY,

  _Neatly printed in_ 18mo. _and bound in_ Cloth, _containing_

  THE ART OF GLASS-BLOWING,

  _Or Plain Instructions for Making the_

  CHEMICAL & PHILOSOPHICAL INSTRUMENTS
  WHICH ARE FORMED OF GLASS;

  Such as

  BAROMETERS, THERMOMETERS, HYDROMETERS,
  _Hour-Glasses_, _Funnels_, _Syphons_,
  TUBE-VESSELS FOR CHEMICAL EXPERIMENTS,
  TOYS FOR RECREATIVE PHILOSOPHY, &c.

  BY A FRENCH ARTIST.

  ILLUSTRATED BY UPWARDS OF ONE HUNDRED FIGURES,
  _Elegantly engraved on Copper plates_.

Artists and Students of the Experimental Sciences will find this work
adapted to aid them effectually in the economical preparation of their
Apparatus; and persons who would willingly occupy their leisure hours
in practising the charming art of working Glass and Enamels with the
Blowpipe, but who have hitherto been deterred by the anticipated
expense of the instruments, and the imaginary difficulties of the
undertaking, are taught herein the simplest, most expeditious, least
expensive, and most effectual methods of working Glass into every
variety of useful or fanciful device.


  PUBLISHED BY BUMPUS & GRIFFIN, SKINNER-STREET, LONDON;
  R. GRIFFIN AND CO. GLASGOW;
  AND STILLIES, BROTHERS, EDINBURGH.




  THE FOLLOWING WORKS, INTENDED TO FORM PART OF
  THE POLYTECHNIC LIBRARY,
  _Are nearly ready for Publication_.

  THE
  DOMESTIC CHEMIST;
  _Comprising Instructions for_
  THE DETECTION OF ADULTERATIONS
  In numerous Articles employed in
  DOMESTIC ECONOMY & THE ARTS.

  _To which is prefixed_,
  THE ART OF DETECTING POISONS IN FOOD AND
  ORGANIC MIXTURES.


_Contents._

    PART I.--INSTRUCTIONS FOR THE DETECTION OF MINERAL POISONS IN
    VEGETABLE OR ANIMAL MIXTURES.--Copper, Lead, Antimony, Arsenic,
    Mercury, Iron, Barytes, Lime, Alumina, Potash, Soda, Sulphuric
    Acid, Nitric Acid, Muriatic Acid.

    PART II.--INSTRUCTIONS FOR THE EXAMINATION OF ARTICLES SUPPOSED
    TO BE ADULTERATED.--Alcohol, Ale, Anchovy Sauce, Arrow-Root,
    Beer, Brandy, Bread, Calomel, Carmine, Cayenne Pepper, Cheese,
    Chocolate, Chrome Yellow, Cinnamon, Cloves, Cochineal, Coffee,
    Confectionery, Crabs' Eyes, Cream, Cream of Tartar, Epsom
    Salts, Flour, Gin, Gum Arabic, Spirits of Hartshorn, Honey,
    Hops, Ipecacuanha, Isinglass, Ketchup, Lakes, Leeches, Lemon
    Acid, Litharge, Magnesia, Milk, Mushrooms, Mustard, Olive Oil,
    Parsley, Pepper, Peruvian Bark, Pickles, Porter, Red Oxide of
    Mercury, Rhubarb, Sal Ammoniac, Salt, Saltpetre, Soap, Soluble
    Tartar, Spanish Liquorice, Spirits, Sugar, Sulphur, Tamarinds,
    Tapioca, Tartaric Acid, Tartar Emetic, Tea, Ultramarine,
    Verdigris, Vermilion, Vinegar, Volatile Oils, Wax, White Lead,
    Wine, Water,(including directions for testing the purity of all
    descriptions of Rain, River, or Spring Water.)

    PART III.--INSTRUCTIONS FOR THE PREPARATION OF THE TESTS EMPLOYED
    IN DOMESTIC CHEMISTRY AND FOR THE PERFORMANCE OF VARIOUS CHEMICAL
    OPERATIONS; WITH DESCRIPTION OF THE GLASSES AND APPARATUS PROPER
    TO BE EMPLOYED.

⁂ The work is written in a popular manner, and intended for the use of
Families, Publicans, Wine and Spirit Merchants, Oilmen, Manufacturers,
Apothecaries, Physicians, Coroners, and Jurymen.--_Price Three
Shillings._




THE PERFUMER’S ORACLE.


The object of this work is to present a comprehensive and practical
account of the Preparation of PERFUMES and COSMETICS, according to
the newest, most successful, and most economical processes. It will
be adapted either for Professional Persons, or for Ladies who may
wish to amuse themselves with this elegant branch of experimental
science.--_Price Three Shillings._

[Illustration:

    _Pl. 2._

_Published by Bumpus & Griffin London, 1831._]

[Illustration:

  _Pl. 3._

_Published by Bumpus & Griffin London, 1831._]

[Illustration:

  _Pl. 4._

_Published by Bumpus & Griffin London, 1831._]




TRANSLATOR’S PREFACE.


The scientific instruments prepared by the glass-blower are numerous
and highly useful: barometers, thermometers, syphons, and many other
vessels constructed of tubes, are indispensable to the student of
physics or chemistry. Some of these instruments are high in price,
and liable to frequent destruction; and those by whom they are much
employed are subject to considerable expense in procuring or replacing
them. It is therefore advisable that he who desires to occupy himself
in the pursuit of experimental science, should know how to prepare
such instruments himself; that, in short, he should become his own
glass-blower. “The attainment of a ready practice in the blowing and
bending of glass,” says Mr. Faraday, “is one of those experimental
acquirements which render the chemist most independent of large towns
and of instrument-makers.”

Unquestionably the best method of learning to work glass is to obtain
personal instructions from one who is conversant with the art: but
such instructions are not easily obtained. The best operators are not
always the best teachers; and to find a person equally qualified and
willing to teach the art, is a matter of considerable difficulty. In
large towns, workmen are too much engaged with their ordinary business
to step aside for such a purpose; and in small towns glass-blowers
are seldom to be found. In most cases, also, they are too jealous of
their supposed _secrets_ to be willing to communicate their methods of
operating to strangers, even when paid to do so.

The following Treatise is a free translation of _L’Art du Souffleur
à la Lampe, par_ T. P. DANGER. The author is employed, in Paris, in
preparing glass instruments for sale, and in teaching others the art
of preparing them. He has presented in this work the most minute
instructions for the working of glass which have ever been offered to
the public. The general processes of the art are so fully explained,
and the experimental illustrations are so numerous, that nothing
remains except the reducing of these instructions to practice to enable
the student to become an adept in the blowing of glass. I trust that,
in publishing this work in an English dress, I may be considered as
aiding in some degree the progress of physical science.

This work contains a description of a cheap blowpipe and a very
convenient lamp; both of them the invention of the author: but any
other kind of lamp or blowpipe may be employed instead of these. The
reader who wishes for a description of the blowpipes generally employed
in England, may consult Mr. GRIFFIN’S _Practical Treatise on the Use of
the Blowpipe in Chemical and Mineral Analysis_.

    _London, September 1831._




AUTHOR’S PREFACE.


The flame of a lamp, or candle, condensed and directed by a current
of air, is exceedingly useful in a great number of arts. The
instrument which is employed to modify flame is the BLOWPIPE. This
is an indispensable agent for jewellers, watch-makers, enamellers,
glass-blowers, natural philosophers, chemists, mineralogists, and,
indeed, for all persons who are occupied with the sciences, or their
application to the arts. Its employment offers immense advantages in
a multitude of circumstances; and the best method of making use of so
powerful an agent ought to be well known to every person who is likely
to be called upon to adopt it.

Students, especially those who desire to exercise themselves in
chemical manipulation, must feel the want of a simple and economical
process, by means of which they could give to glass tubes, of which
they make great use, the various forms that are necessary for
particular operations. How much reason have they to complain of the
high price of the instruments of which they make continual use! The
studies of a great number are shackled from want of opportunity to
exercise themselves in manipulation; and many, not daring to be at
the expense of a machine of which they doubt their ability to make
an advantageous use, figure to themselves the employment of the
glass-blower’s apparatus as being beset with difficulties, and so rest
without having even an idea of the numberless instruments which can be
made by its means.

Many persons would very willingly occupy their leisure time in
practising the charming art of working glass and enamels with the
blowpipe; but the anticipated expense of the apparatus, and the
difficulties which they imagine to foresee in the execution of work of
this kind, always repels them.

The new species of blowpipe which we have offered to the public, and
which has received the approbation of the Society for the Encouragement
of Arts, obviates all these inconveniences: its moderate price, its
portability, and the facility with which it can be used, adapt it to
general employment.

But we should not believe that we had attained the end which we
had proposed to ourselves if we had not placed young students in a
situation to repeat at their own houses, at little cost, and with the
greatest facility, the experiments which are necessary to familiarise
them with the sciences. It is with such a view that we present to them
this little Treatise, which is destined to teach them the simplest, the
most expeditious, the least expensive, and the most effectual methods
of constructing themselves the various instruments which they require
in the prosecution of their studies.

The word _glass-blower_, generally speaking, signifies a workman who
occupies himself in making of glass and enamel, the instruments,
vessels, and ornaments, which are fabricated on a larger scale in
the glass-houses: but the domain of the sciences having laid the art
of glass-blowing under contribution, the artists of the lamp have
divided the labours thereof. Some apply themselves particularly to the
construction of philosophical and chemical instruments; others occupy
themselves with little ornamental objects, such as flowers, &c.; and,
among the latter, some manufacture nothing but pearls, and others only
artificial eyes. Finally, a few artists confine themselves to drawing
and painting on enamel, which substance is previously applied to
metallic surfaces by means of the fire of a muffle.

As we intend to treat separately of these different branches of the
art, we commence with that of which the manipulation is the simplest.

    _Paris, 1829._




CONTENTS.


                         Page

  I.--_Instruments employed in Glass-Blowing_                        1

      The Blowpipe                                                   1

      The Glass-Blower’s Table                                       3

      The Eolipyle                                                   5

      Blowpipe with Continued Current                                5

      The Lamp                                                       8

      The Candlestick                                                9

      Combustibles                                                   9

          Oil, Tallow, &c.                                           9

          The Wicks                                                 10

          Relation between the Diameter of the
          Beaks of the Blowpipe and the Wicks
          of the Lamp                                               12

  II. _Preliminary Notions of the Art of Glass-Blowing_             16

      The Flame                                                     16

      Places fit to work in                                         19

      Means of obtaining a Good Fire                                19

      Choice and Preservation of Glass                              22

      Preparation of Glass Tubes before heating them                25

      Method of presenting Tubes to the Fire, and of working them
          therein                                                   26

  III. _Fundamental Operations in Glass-Blowing_                    30

      1. Cutting                                                    31
      2. Bordering                                                  34
      3. Widening                                                   36
      4. Drawing-out                                                36
      5. Choking                                                    37
      6. Sealing                                                    38
      7. Blowing                                                    39
      8. Piercing                                                   46
      9. Bending                                                    48
      10. Soldering                                                 49

  IV. _Construction of Chemical and Philosophical Instruments_      54

      Adapters                                                      55

      Apparatus for various Instruments                             55

      Archimedes’s Screw                                            57

      Areometers                                                    71

      Barker’s Mill                                                 57

      Barometers                                                    58

          Cistern Barometer                                         58

          Dial Barometer                                            58

          Syphon Barometer                                          59

          Stop-cock Barometer                                       59

          Compound Barometers                                       59

          Gay-Lussac’s Barometer                                    60

          Bunten’s Barometer                                        61

          Barometer pierced laterally for Demonstrations            61

      Bell Glasses for Experiments                                  61

      Blowpipe                                                      62

      Capsules                                                      63

      Cartesian Devils                                              64

      Communicating Vases                                           65

      Cryophorus                                                    55

      Dropping Tubes                                                65

      Fountains                                                     66

          Fountain of Circulation                                   66

          Fountain of Compression                                   67

          Intermitting Fountain                                     68

          Hero’s Fountain                                           68

      Funnels                                                       68

      Hour Glasses                                                  70

      Hydraulic Ram                                                 70

      Hydrometers                                                   71

          Baumé’s Hydrometer                                        71

          Nicholson’s Hydrometer                                    73

          Hydrometers with two, three, or four branches             74

      Manometers                                                    74

      Mariotte’s Tube                                               75

      Phosphoric Fire-bottle                                        75

      Pulsometer                                                    75

      Pump                                                          76

      Retorts for Chemical Experiments                              76

      Rumford’s Thermoscope                                         77

      Syphons                                                       78

      Spoons                                                        80

      Spirit Level                                                  80

      Test Glass with a foot                                        80

      Thermometers                                                  81

          Ordinary Thermometer                                      81

          Dial Thermometer                                          83

          Chemical Thermometer                                      84

          Spiral Thermometer                                        85

          Pocket Thermometer                                        86

          Maximum Thermometer                                       86

          Minimum Thermometer                                       86

          Bellani’s Maximum Thermometer                             87

          Differential Thermometer                                  87

      Thermoscope                                                   77

      Tubes bent for various purposes                               88

      Vial of the four Elements                                     90

      Water Hammer                                                  91

      Welter’s Safety Tubes                                         92


  V. _Graduation of Chemical and Philosophical Instruments_         93

      Of the substances employed in the preparation of these
         instruments                                                93

      Of Graduation in general                                      94

      Examination of the Bore of Tubes                              95

      Division of Capillary Tubes into parts of equal Capacity      95

      Graduation of Gas Jars, Test Tubes, &c.                       97

      Graduation of Hydrometers                                     99

      Graduation of Barometers                                     103

      Graduation of the Manometer                                  105

      Graduation of Thermometers                                   105

      Graduation of Rumford’s Thermoscope                          112

      Graduation of Mariotte’s Tube                                112




THE

ART OF GLASS-BLOWING.

I.--_Instruments employed in Glass-Blowing._


On seeing, for the first time, a glass-blower at work, we are
astonished at the multitude and the variety of the modifications to
which he can make the glass submit. The small number and the simplicity
of the instruments he employs, is also surprising. The blowpipe, or, in
its place, the glass-blower’s bellows and a lamp, are indeed all that
are indispensable.


THE BLOWPIPE.

Originally, the blowpipe was only a simple, conical tube, more or less
curved towards its point, and terminated by a very small circular
opening. By means of this, a current of air was carried against the
flame of a candle, and the inflamed matter was directed upon small
objects, of which it was desirable to elevate the temperature. Workers
in metal still derive immense advantages from the use of this little
instrument: they employ it in the soldering of very small articles,
as well as for heating the extremities of delicate tools, in order
to temper them. But since the blowpipe has passed into the hands of
mineralogical chemists, its form has been subjected to a series of
very curious and important modifications. In spite, however, of these
ameliorations, which rendered the instrument better adapted for the
uses to which it was successively applied, we are far from having
drawn from it all the advantages to which we might attain, were its
employment not as fatiguing as it is difficult. We require no other
proof of this than the small number of those who know well how to make
use of the blowpipe.

The most economical blowpipe is a tube of glass, bent near one end,
and pointed at its extremity. A bulb is blown near that part of the
tube which corresponds with the curvature (pl. 3, fig. 7.) This bulb
serves as a reservoir for moisture deposited by the air blown into the
tube from the mouth. If you employ a tube without a bulb, the moisture
is projected in drops into the flame, and upon the objects heated by
it--an effect which is very inconvenient in practice. To put this
instrument into action, accustom yourself to hold the mouth full of
air, and to keep the cheeks well inflated, during a pretty long series
of alternate inspirations and expirations; then, seizing lightly with
the lips the mouth of the blowpipe, suffer the air compressed by the
muscles of the cheeks, which act the part of a bellows, to escape by
the beak of the blowpipe, which you will be able to do without being
put to the least inconvenience with regard to respiration. When the
air contained in the mouth is pretty nearly expended, you must take
advantage of an inspiration, to inflate the lungs afresh; and thus
the operation is continued. You must never blow through the tube by
means of the lungs; first, because air which has been in the lungs is
less proper for combustion than that which has merely passed through
the nose and mouth; secondly, because the effort which it would be
necessary to make, to sustain the blast for only a short time, would by
its frequent repetition become very injurious to your health.

The jet of flame produced by the mouth-blowpipe can only be used to
heat small objects: when instruments of a considerable bulk have to be
worked, it is customary to employ the _lamp_, or _glass-blower’s table_.


THE GLASS-BLOWER’S TABLE.

Artists give this name to an apparatus which consists of the following
articles:--

1. A _Table_, below which is disposed a _double bellows_, capable of
being put in motion by means of a pedal. This bellows furnishes a
continued current of air, which can be directed at pleasure by making
it pass through a tube terminating above the table in a sharp beak. The
bellows with which the glass-blower’s tables are commonly furnished
have very great defects. The irregular form which is given to the
pannels diminishes the capacity of the instruments, without augmenting
their advantages. If we reflect an instant on the angle, more or less
open, which these pannels form when in motion, we instantly perceive
that the weight with which the upper surface of a bellows is charged,
and which always affords a vertical pressure, acts very unequally on
the arm of a lever which is continually changing its position. This
faulty disposition of the parts of the machine has the effect of
varying every instant the intensity of the current of air directed upon
the flame. All these inconveniences would disappear, were the upper
pannel, like that in the middle, disposed in such a manner as to be
always horizontal. It ought to be elevated and depressed, in its whole
extent, in the same manner; so that, when charged with a weight, the
pressure should be constantly the same, and the current of air uniform.

2. A _lamp_, of copper or tin plate.--The construction of this article,
sufficiently imperfect until the present time, has varied according to
the taste of those who have made use of it. We shall give, farther on,
the description of a lamp altogether novel in its construction.

3. The glass-blower’s table is generally furnished with little
_drawers_ for holding the tools employed in modelling the softened
glass. Careful artists have the surface of their table coated with
sheet iron, in order that it may not be burned by the hot substances
that fall, or are laid upon it. As glass-blowers have frequent occasion
to take measures, it is convenient to have the front edge of the table
divided into a certain number of equal parts, marked with copper nails.
This enables the workman to take, at a glance of the eye, the half,
third, or fourth of a tube, or to give the same length to articles
of the same kind, without having perpetual recourse to the rule and
compasses. But when it is desirable to have the tubes, or the work,
measured with _greater exactness_ than it can be measured by this
method, the rule and the compasses can be applied to.


THE EOLIPYLE.

We shall merely make mention of this instrument. It is a globular
vessel, commonly formed of brass. If filled with a very combustible
liquor, such as alcohol, and strongly heated, it affords a rapid
current of vapour, which, if directed by means of a fine beak into
the middle of a flame, produces the same effect as the air which
issues from a blowpipe. The eolipyle is a pretty toy, but not a good
instrument for a workman, its action being too irregular.


BLOWPIPE WITH CONTINUED CURRENT.

It is after having, during a long period, made use of the instruments
of which we have spoken, and fully experienced their inconveniences,
that, aware of the indispensable necessity for such instruments in the
arts and sciences, we have thought it our duty to make known to the
public _a New Apparatus_, which is, not only calculated to fulfil the
same purposes, but presents advantages which it is easy to appreciate.
The price of it is only the sixth part of that of the glass-blower’s
table[1]. It is very portable, and capable of being attached to any
table whatever. It unites the advantages of not fatiguing the workman,
of leaving his hands free, and of rendering him absolute master of the
current of air, which he can direct on the flame either of the lamp or
the candle,--advantages which are not offered in the same degree even
by the table of the glass-blower.

[1] In Paris, the blowpipe which is here described is sold for six
francs (five shillings English); or, with the improved lamp and
candlestick, twelve francs.

The instrument which we have presented is, properly speaking, nothing
but a simple blowpipe, C, (pl. 1, fig. 19) communicating with a
bladder, or leather bag, fixed on E, which is kept full of air by
means of a bent tube, D, through which the operator blows occasionally
with the mouth. This tube is closed at its inferior extremity, F, by a
valve, which permits the passage of air into the reservoir, but not of
its return, so that the air can only escape by the beak of the blowpipe.

The valve at F is constructed in the following manner:--At about two
inches from the end of the tube a contraction is made, as represented
at _a_, pl. 1, fig. 24. This reduces the internal diameter of the
tube about one-third. A small conical piece of cork or wood is now
introduced into the tube in the manner represented by _c_. The base of
the cone must be large enough to close the tube at the point where it
is contracted; it must, however, not be so large as to close the tube
at the wide part. A brass pin is inserted in the point of the cone, as
is shewn in the figure. Between the cone and the end of the tube, the
piece of wood, _b_, is fixed; the shape of this piece of wood is best
shewn by figure 25, on the same plate. There is a hole in the centre,
in which the pin of the cork cone can move easily. The cone or valve
is therefore at liberty to move between the contraction _a_, and the
fixture _b_. Consequently, when air is blown into the tube at _e_, the
valve is forced from the contraction, falls into the position indicated
by the dotted lines _d_, and allows the air to pass by its sides.
When, on the contrary, the operator ceases to blow, the valve is acted
upon by the air in the bladder, which, pressing back at _f_, drives
the valve close against the contraction, and effectually closes the
aperture. A slight hissing is heard, but when the contraction is well
made, and the cork is good, an extremely small quantity of air escapes.

The workman, seated before the table where he has fixed his instrument,
blows from time to time, to feed the reservoir or bladder, which,
being pressed by a system of strings stretched by a weight, produces
an uniform current of air. The force of this current of air can be
modified at pleasure, by pressing the reservoir more or less between
the knees. (Fig. 22 represents a blowpipe complete, formed not of
glass, but of brass tubes. Fig. 22, _bis_, represents the bladder or
reservoir appertaining to this blowpipe.)

M. GAULTIER DE CLAUBRY, who was charged by the Committee of Chemical
Arts of the Society of Encouragement (of Paris) to make a report on
this instrument, was astonished at the facility with which the author,
in his presence, reduced the oxide of cobalt to the metallic state, and
fused the metal to a globule; an experiment which even M. Berzelius
could not perform with the simple blowpipe, since he expressly says,
in his work on that instrument, that oxide of cobalt suffers no change
when heated before the blowpipe. The results obtained with cast iron,
oxide of tin, &c.--experiments which are exhibited every day at the
public lectures given by the author--evidently prove the superiority of
this apparatus over all the blowpipes that have hitherto been contrived.

A detailed account of the glass tubes belonging to this improved
blowpipe will be found in the fourth part of this work, at the article
_Blowpipe_.


THE LAMP.

While occupied in rendering popular, if we may so speak, the use of the
_blowpipe_--an instrument which is so advantageous in a great number
of circumstances--we have also endeavoured to improve _the lamp_,
which has, until the present time, been used by all those who employ
the glass-blower’s table. The lamp which we recommend (pl. 1, fig.
23) is of a very simple construction. It possesses the advantages of
giving much less smoke than the old lamp, and of being cleaned with
the greatest facility. It also gives sensibly more heat; because the
portion of flame which, in the common lamps, rises perpendicularly,
and is not used, is, in this case, beaten down by a cap or hood, and
made to contribute to the force of the jet. This cap also keeps the
flame from injuring the eyes of the operator, and destroys the smoke to
such an extent, that the large hoods with which glass-blowers commonly
garnish their work table, to carry off the smoke, become unnecessary.
This is a peculiar advantage in the chamber of a student, where a large
hood or chimney can seldom be conveniently prepared.


THE CANDLESTICK.

For mineralogical researches, chemical assays, and the soldering of
small objects, as in jewellery, we recommend the use of a little
candlestick, which, by means of a spring fixed to the bottom, maintains
the candle always at the same height. A reservoir, or shallow cup,
formed at the top of the candlestick, to hinder the running away of the
tallow or wax, allows the operator to consume the fragments of tallow
or grease which are ordinarily lost in domestic economy. There is a
little hole in the centre of the cup or upper part of the candlestick,
through which the wick of the candle passes. _o_, pl. 1, fig. 22, is a
representation of this candlestick.


COMBUSTIBLES.

_Oil_, _Tallow_, _&c._--Among the substances which have been employed
to feed the fire of the glass-blower’s lamp, those to which the
preference is to be given are wax, olive oil, rape oil, poppy oil, and
tallow. Animal oils, such as bone oil and fish oil, are much esteemed
by some glass-blowers, who pretend that with these substances they
obtain better results than with other combustibles. Nevertheless,
animal oils, generally speaking, do not give so much heat as purified
rape oil, while they exhale an odour which is extremely disagreeable.

As to alcohol, which is sometimes used with the eolipyle, its
combustion furnishes so feeble a degree of heat that its employment
cannot be recommended.

Purified rape oil is that of which the use is the most general. Next
to olive oil and wax, it affords the greatest heat, and the least
smoke. But, in a word, as in the working of glass, the operator has
more need of a bright flame without smoke, than of a high temperature,
any combustible may be employed which is capable of furnishing a flame
possessing these two qualities. The vegetable oils thicken, and suffer
alterations more or less sensible, when they are long exposed to the
action of the air. They should be chosen very limpid, and they may be
preserved in that state by being enclosed in bottles, which should be
kept quite full and well corked.

_The Wicks._--There has never been any substance so generally used for
wicks as cotton; some glass-blowers, indeed, have employed wicks of
asbestus, but without deriving from them the advantages which might
have been expected; the greater number, therefore, keep to cotton.

But it has been observed that cotton which has been for some time
exposed to the air no longer possesses the good properties for which
glass-blowers esteem it. The alteration of the cotton is probably
brought about by the dust and water which the air always holds in
suspension. Such cotton burns badly, forms a bulky coal, and permits
with much difficulty the capillary ascension of the liquid which serves
to support the flame; so that it is impossible to obtain a good fire,
and necessary to be incessantly occupied in snuffing the wick. Cotton
is equally subject to alteration when lying in the lamp, even though
impregnated with oil. You should avoid making use of wicks that are too
old. When you foresee that you will remain a long time without having
occasion to employ the lamp, pour the oil into a bottle, which can be
corked up, and let the wick be destroyed, previously squeezing from it
the oil which it contains.

It is indispensable to make use of none but new and good cotton; it
should be clean, soft, fine, and not twisted. It is best to preserve
it in boxes, after having folded it in many double papers, to exclude
dust and moisture. When you wish to make wicks, take a skein of cotton
and cut it into four or six pieces, dispose them side by side in such a
manner as to make a bundle, more or less thick, and eight or ten inches
in length; pass a large comb lightly through the bundle, to lay the
threads even, and tie it gently at each end, to keep the threads from
getting entangled.

_Relation between the diameters of the beaks of the blowpipe, and the
wicks of the lamp._--We believe that we cannot place better than here
a few observations respecting the size of the opening in the beak of
the blowpipe, considered in relation to the size of the wick of the
lamp. These observations will probably be superfluous to those who are
already conversant with the use of the blowpipe; but as every thing is
interesting to beginners, who are frequently stopped in their progress
by very slight difficulties, and as this Treatise is particularly
designed for beginners, we do not hesitate to enter into the minutest
details on subjects which we deem interesting.

The point of your blowpipe should be formed in such a manner, that you
can fix upon it various little beaks or caps, the orifices in which,
always perfectly round, ought to vary in size according to the bulk
of the flame upon which you desire to act. You cannot, without this
precaution, obtain the maximum of heat which the combustion of the oil
is capable of affording. This employment of little moveable caps offers
the facility of establishing a current of air, greater or smaller,
according to the object you wish to effect; above all, it allows you to
clean with ease the cavity or orifice of the beak, as often as it may
be necessary.

These caps can be made of different materials. It is most advisable to
have them made of copper or brass; those which are formed of tin plate
(white iron), and which are commonly used in chemical laboratories, are
the worst kind of all. They soon become covered with grease or soot,
which either completely closes up the orifices, or, at least, very soon
alters the circular form which is necessary to the production of a good
fire. Glass caps are less liable to get dirty, and are much cheaper
than the above; but, on the other hand, they have the disadvantage
of being easily melted. This can to a certain extent be remedied by
making the points of very thick glass, and by always keeping them at
some distance from the flame. Moreover, as you can make them yourself
when you are at leisure, their use is very commodious. If they are to
be used with the blowpipe described in this work, they must be fixed
in the cork that closes the passage through which the current of air
arrives. _C c_ and _C´ c_ (pl. 1, fig. 19) are two glass beaks, _c c_
are the corks, which can indifferently be adapted to _c_, in the wooden
vice, by which the various parts of the blowpipe are connected when it
is in action.

Of whatever material the beak may be made, its orifice must be
perfectly round, and the _size_ of the orifice, as we have before
observed, must have a relation to the size of the wick which is to
be used with it. You can ascertain the diameters of the orifices by
inserting into them a little plate of brass, having the form of a long
isoceles triangle, such as is represented by pl. 1, fig. 2. It should
be an inch long, the twelfth of an inch wide at one end, and diminish
to nothing at the other. When divided into eight equal parts, it will
give, at the divisions, the respective proportions of 1, 2, 3, 4, 5,
6, 7 _eighths_ of the diameter at the wide end, as is exemplified by
the figure above referred to. We have stated in the following table
the relative diameters which long experience has recommended to us,
as being adapted to produce the greatest effect; yet it is not to
be imagined that these proportions are mathematically correct and
indispensable for the obtaining of good results. A sensible difference
of effect would be perceived, however, were these proportions departed
from in a notable manner.

  +-----------------+---------------------------+------------------+
  |                 |                           |                  |
  | Diameter of the |      Diameter of the      |Height of the wick|
  |      wick,      |      orifice of the       |above the surface |
  |  _in inches_.   |           beak,           |   of the oil,    |
  |                 |  _in parts of an inch_.   |   _in inches_.   |
  |                 |                           |                  |
  +-----------------+---------------------------+------------------+
  |       ¼         |           96th            |       ½          |
  |       ½         |           48th            |       ½          |
  |      1          |           24th            |       ¾          |
  |      1½         |           16th            |      1           |
  |      2          |           12th            |      1¼          |
  +-----------------+---------------------------+------------------+

It must be mentioned, that this table has been formed from experiments
made with a glass-blower’s lamp of the ordinary construction; so that,
with the new lamp with the hood, described in this work, it will not
be necessary to employ wicks of so great a bulk, nor yet to elevate
them so much above the level of the oil, in order to produce the same
effect. Hence there will be a very considerable saving in oil.

The wicks of a quarter of an inch in diameter are only adapted
for mineralogieal examinations, for soldering very fine metallic
substances, and for working very small tubes. When the objects are
of considerable bulk, it is in general necessary to have a flame
sufficiently large to cover the whole instrument, or at least all the
portion of the instrument which is operated upon at once. For working
tubes, of which the sides are not more than the twelfth of an inch in
thickness, you should have a wick at least as wide as the tube that is
worked upon. The diameter of the lamp-wick usually employed is _one
inch_; a wick of this size is sufficient for all the glass instruments
which are in common use.




THE

ART OF GLASS-BLOWING.

II.--_Preliminary Notions of the Art._


THE FLAME.

It is only by long habitude, and a species of routine, that workmen
come to know, not only the kind of flame which is most proper for
each object they wish to make, but the exact point of the jet where
they ought to expose their glass. By analysing the flame, upon the
knowledge of which depends the success of the work, we can immediately
obtain results, which, without that, could only be the fruit of long
experience.

Flame is a gaseous matter, of which a portion is heated to the point of
becoming luminous; its form depends upon the mode of its disengagement,
and upon the force and direction of the current of air which either
supports its combustion or acts upon it mechanically. (Pl. 1, fig. 1.)

The flame of a candle, burning freely in still air, presents in
general the form of a pyramid, of which the base is supported on
a hemisphere. It consists of four distinct parts: the immediate
products of the decomposition of the combustible by the heat which is
produced, occupy the centre, _o_, where they exist in the state of an
obscure gaseous matter, circumscribed by a brilliant and very luminous
envelope, _s_; the latter is nothing but the obscure matter itself, in
the circumstances where, on coming into contact with the atmosphere,
it combines with the oxygen which exists therein, and forms what is
properly called _flame_.

The blueish light which characterises the inferior part of the flame,
_s_, is produced by a current of cold air, which, passing from below
_upwards_, hinders the combustion from taking place at the bottom of
the flame, at the _same_ temperature that exists in the parts of the
flame not immediately subject to this influence.

Finally, on observing attentively, we perceive a fourth part, which
is but slightly luminous, and exists as an envelope of all the other
parts of the flame. The greatest thickness of this envelope corresponds
with the summit of the flame. From this point it gradually becomes
thinner, till it arrives at the lowest part of the blueish light, where
it altogether disappears. It is in this last-described portion of the
flame that the combustion of the gas is finished, and there it is that
we find the seat of the most intense heat which the flame of the candle
affords. If we compare the temperature of the different parts of the
flame, we find that the _maximum_ of heat forms a ring corresponding to
the zone of insertion, A A; a point which is the limit of the superior
extremity of the blueish light.

When the flame is acted upon by the blowpipe, it is subject to two
principal modifications:--

1. If, by means of a blowpipe with a very fine orifice, you direct a
current of air through the middle of the flame, you project a portion
of the flame in the direction of the blast. The jet thus formed appears
like a tongue of fire, blueish, cylindrical, straight, and very long;
the current of air occupies its interior. This flame is enveloped on
all sides by an almost invisible light, which, extending beyond the
blue flame, forms a jet, A´ B, very little luminous, but possessing an
extremely high temperature. It is at the point A´, which corresponds
with the extremity of the blue flame, that the _maximum_ of heat is
found. The extreme point of the jet B possesses a less degree of heat.
This flame is adapted for mineralogical assays, for soldering, for
working enamels, and in general for all small objects.

2. When the orifice of the blowpipe is somewhat large, or when (the
orifice being capillary) the current of air is very strong, or the
beak is somewhat removed from the flame, the jet of fire, instead of
being prolonged into a pointed tongue, is blown into a brush. It makes
then a roaring noise, and spreads into an irregular figure, wherein
the different parts of the flame are confounded beyond the possibility
of discrimination. This flame is very proper for the working of
glass, and particularly of glass tubes; it ought to be clear and very
brilliant, and above all should not deposit soot upon cold bodies
suddenly plunged into it. The _maximum_ of temperature in this flame is
not well marked; we can say, however, that in general it will be found
at about two-thirds of the whole length of the jet. As this roaring
flame contains a great quantity of carburetted hydrogen, and even of
vapour of oil, escaped from combustion, it possesses a disoxidizing or
reducing property in a very high degree.


PLACES FIT TO WORK IN.

Every place is adapted for a workshop, provided it is not too light
and the air is tranquil. The light of the lamp enables one to work
with more safety than day-light, which does not permit the dull-red
colour of hot glass to be seen. Currents of cold air are to be avoided,
because they occasion the fracture of glass exposed to them on coming
out of the flame.


MEANS OF OBTAINING A GOOD FIRE.

The lamp should be firmly seated upon a steady and perfectly horizontal
table, and should be kept continually full of oil. The oil which
escapes during the operation, from the lamp into the tin-stand placed
below it, should be taken up with a glass tube having a large bulb, and
returned to the lamp.

When you set to work, the first thing you have to do is to examine the
orifice of the beak. If it is closed, or altered in form, by adhering
soot, you must carefully clean it, and open the canal by means of a
needle or fine wire. In the next place, you freshen the wick by cutting
it squarely, and carrying off with the scissars the parts which are
carbonised. You then divide it into two principal bundles, such as C, K
(pl. 1, fig. 21), which you separate sufficiently to permit a current
of air, directed between the two, to touch their surfaces lightly,
without being interrupted in its progress. By pushing the bundles
more or less close to one another, and by snuffing them, you arrive
at length at obtaining a convenient jet. It is a good plan to allow,
between the two principal bundles and at their inferior part, a little
portion of the wick to remain: you bend this down in the direction of
the jet, and make it lie immediately beneath the current of air.

The wick must be prevented from touching the rim of the lamp, in order
to avoid the running of the oil into the stand of the lamp. This is
easily managed by means of a bent iron-wire, disposed as it is in the
lamp described in this work; see pl. 1, fig. 23, where the wire is
seen in an elevated position. When the wick is in the lamp, the wire
is brought down round the wick and level with the surface of the lamp.
A few drops of oil of turpentine, spread on the wick, makes it take
fire immediately, over its whole extent, on the approach of an inflamed
substance.

To obtain a good fire, it is necessary to place the lamp in such a
position that the orifice of the blowpipe shall just touch the exterior
part of the flame. The beak must not enter the flame, as it can then
throw into the jet only an inconsiderable portion of the ignited
matter. See pl. 1, fig. 20. On the other hand, if the lamp be too far
away from the blowpipe, the flame becomes trembling, appears blueish,
and possesses a very low degree of heat.

For mineralogical experiments, and for operations connected with
watch-making and jewellery, the current of air should project the flame
horizontally. For glass-blowing, the flame should be projected in the
direction intimated by the arrow in pl. 1, fig. 20--that is to say,
under an angle of twenty or twenty-five degrees.

The current of air ought to be constant, uniform, and sufficiently
powerful to carry the flame in its direction. When it is not strong
enough to produce this effect, it is necessary to add weights to the
bellows or the bladder, according as the glass-blowers' table or our
lamp is employed. The point to which you should apply, in the use of
these instruments, is to enable yourself to produce a current of air
so uniform in its course that the projected flame be without the least
variation.

Finally, when you leave off working you should extinguish the flame, by
cutting off the inflamed portion of the wick with the scissars. This
has the double advantage of avoiding the production of a mass of smoke
and of leaving the lamp in a fit state for another operation.


CHOICE AND PRESERVATION OF GLASS.

The only materials employed in the fabrication of the objects described
in this Treatise, are tubes of common glass or of flint-glass. They
can be had of all diameters, and of every variety of substance. They
are commonly about three feet long, but some are found in commerce
which are six feet in length. You should choose tubes that are very
uniform--that is to say, straight and perfectly cylindrical, both
inside and outside. A good tube should have the same diameter from one
end to the other, and the sides or substance of the glass should be of
equal thickness in every part. This is indispensable when the tubes
are to have spherical bulbs blown upon them. We shall describe, in the
article _Graduation_, the method of ascertaining whether or not a tube
is uniform in the bore.

The substance of the glass should be perfectly clear, without bulbs, or
specks, or stripes. The tubes are so much the more easy of use, as the
glass of which they are made is the more homogeneous. Under this point
of view, the white glass, known in commerce by the name of crystal or
flint-glass, is preferable to common glass: it is more fusible, less
fragile, and less liable to break under the alternations of heat and
cold; but it is dearer and heavier, and has the serious disadvantage
of becoming permanently black when exposed to a certain part of the
flame. This is an effect, the causes and consequences of which will be
explained in a subsequent chapter.

You must take care never to employ flint-glass for instruments
which are to be submitted to the action of certain fluids--such as
sulphuretted and phosphuretted hydrogen, and the hydro-sulphurets; for
these compounds are capable of decomposing flint-glass, in consequence
of its containing oxide of lead. In general, hard common glass is
preferable to flint-glass for all instruments which are to be employed
in chemistry. Flint-glass should only be used for ornamental objects,
and for the barometers, thermometers, and other instruments employed in
philosophical researches.

It sometimes happens that glass tubes lose their transparence and
ductility, and suddenly become almost infusible, in the fire of the
lamp: this effect takes place when they have been kept for some time
in a melted state. It is then almost impossible to bring them back to
their original condition; it can only be done by exposing them for a
long time to an exceedingly high temperature. You can prevent this
accident by working such kind of glass with considerable rapidity,
and in a pretty brisk fire. There are tubes, however, which vitrify
so promptly that it is only a person well versed in the art who can
make good use of them. It is best not to employ such glass. But how
can it be discriminated before-hand? It is experience, sooner than
any characters capable of description, that will teach you how to
make choice of good glass; nevertheless we have observed, that,
among the glass tubes which occur in commerce, those possessing a
very _white colour_ manifest this bad quality most particularly. It
may be observed, that, for tubes which are to have thin sides, this
vitrifiable sort of glass is better than any other.

For certain philosophical instruments it is necessary to employ flat
tubes. These are formed of flint-glass, are very small, and have a
canal or bore, which, instead of being round, as in common tubes,
has the form of a long and very flat oval. This disposition has the
advantage of rendering more perceptible the column of liquid that may
be introduced, and which in a round canal would scarcely be visible. In
choosing this sort of tubes, carefully avoid those of which the canal
is twisted, and not found to be in the same plane, in the whole length
of the tube.

The tubes should be sorted, according to their sizes and qualities,
and should be deposited in large drawers or on long shelves, in such
a manner as to be equally supported through their whole extent. They
should also be sheltered from dust and from moisture. If you cannot
conveniently warehouse them in this manner, you should tie them up in
parcels, and support them in a perpendicular position. It is a very
bad plan to place them in an inclined direction, or to support them by
their extremities on wooden brackets, as it is the fashion to do in
chemical laboratories; because, as the tubes are then supported only
at certain points, they bend, in course of time, under the influence
of their own weight, and contract a curvature which is extremely
prejudicial in certain instruments, and which it is almost impossible
to correct.


PREPARATION OF TUBES BEFORE HEATING THEM.

Before presenting a tube to the flame, you should clean it well both
within and without, in order to remove all dust and humidity. If
you neglect to take this precaution, you run the risk of cracking
or staining the glass. When the diameter of the tube is too small
to permit of your passing a plug of cloth or paper to clean its
interior, you can accomplish the object by the introduction of water,
which must, many times alternately, be sucked in and blown out, until
the tube is deemed clean. One end of it must then be closed at the
lamp, and it must be gradually exposed to a charcoal fire, where, by
raising successively all parts of the tube to a sufficiently high
temperature, you endeavour to volatilize and expel all the water it
contains. In all cases you considerably facilitate the disengagement
of moisture by renewing the air in the tube by means of a bottle of
Indian-rubber fastened to the end of a long narrow tube, which you
keep in the interior of the tube to be dried during the time that it
is being heated. You can here advantageously substitute alcohol for
water, as being much more volatile, and as dissolving greasy matters;
but these methods of cleansing should only be employed for valuable
objects, because it is extremely difficult fully to expel moisture from
a tube wherein you have introduced water, and because alcohol is too
expensive to be employed where there is no particular necessity.

When the tubes no longer contain dust, or moisture, you measure them,
and mark the divisions according to the sort of work which you propose
to execute.


METHOD OF PRESENTING TUBES TO THE FIRE, AND OF WORKING THEM THEREIN.

The two arms are supported on the front edge of the table, and the
tube is held with the hands either above or below, according as it may
be necessary to employ more or less force, more or less lightness.
You ought, in general, to hold the tube _horizontally_, and in such a
manner that its direction may be perpendicular to that of the flame.
Yet, when you wish to heat at once a large portion of the tube, or to
soften it so that it shall sink together in a particular manner, as in
the operation of sealing, you will find it convenient to _incline_ the
tube, the direction of which, however, must always be such as to turn
the heated part continually towards you.

We are about to give a general rule, upon the observance of which we
cannot too strongly insist, as the success of almost every operation
entirely depends upon it. The rule is, _never to present a tube to the
flame without_ CONTINUALLY TURNING _it_; and turning it, too, with
such a degree of rapidity that every part of its circumference may be
heated and softened to the same degree. As melted glass necessarily
tends to descend, there is no method of preventing a heated tube from
becoming deformed but that of continually turning it, so as to bring
the softened part very frequently uppermost. When you heat a tube
near the middle, the movement of the two hands must be _uniform_ and
_simultaneous_, or the tube will be twisted and spoiled.

When the tubes have thick sides, they must not be plunged _into_ the
flame until they have previously been strongly heated. You expose them
at first to the current of hot air, at some inches from the extremity
of the jet; you keep them there some time, taking care to turn them
continually, and then you gradually bring them towards, and finally
into, the flame. The thicker the sides of the tubes are, the greater
precaution must be taken to elevate the temperature gradually: this is
the only means of avoiding the fractures which occur when the glass
is too rapidly heated. Though it is necessary to take so much care
with large and thick tubes, there are, on the contrary, some tubes
so small and so thin that the most sudden application of the fire is
insufficient to break them. Practice soon teaches the rule which is to
be followed with regard to tubes that come between these extremes.

Common glass ought to be fused at the _maximum_ point of heat; but
glass that contains oxides capable of being reduced at that temperature
(such as flint-glass) require to be worked in that part of the flame
which possesses the highest oxidating power. If you operate without
taking this precaution, you run the risk of decomposing the glass.
Thus, for example, in the case of flint-glass, you may reduce the oxide
of lead, which is one of its constituents, to the state of metallic
lead. The consequence of such a reduction is the production of a black
and opaque stain upon the work, which can only be removed by exposing
the glass, during a very long time, to the extremity of the jet.

You must invariably take the greatest care to keep the flame from
passing into the interior of the tube; for when it gets there it
deposits a greasy vapour, which is the ordinary cause of the dirt
which accumulates in instruments that have been constructed without
sufficient precaution as to this matter.

In order that you may not blacken your work, you should take care to
snuff the wick of the lamp whenever you perceive the flame to deposit
soot.

You can judge of the _consistence_ of the tubes under operation as
much by the _feel_ as by the _look_ of the glass. The degree of heat
necessary to be applied to particular tubes, depends entirely upon
the objects for which they are destined. As soon as the glass begins
to feel soft, at a _brownish-red heat_, for example, you are at the
temperature most favourable to good _bending_. But is it intended to
_blow a bulb_? The glass must, in this case, be completely melted,
and subjected to a full _reddish-white heat_. We shall take care,
when speaking hereafter of the different operations to be performed,
to mention the temperature at which _each_ can be performed with most
success.

When an instrument upon which you have been occupied is finished, you
should remove it from the flame _gradually_, taking care to _turn_ it
continually, until the glass has acquired sufficient consistence to
support its own weight without becoming deformed. Every instrument
formed thus of glass requires to undergo a species of _annealing_,
to enable it to be preserved and employed. To give the instrument
this annealing, it is only necessary to remove it from the flame very
gradually, allowing it to repose some time in each _cooler_ place to
which you successively remove it. The thicker or the more equal the
sides of the glass, the more carefully it requires to be annealed. No
instrument should be permitted to touch cold or wet bodies while it is
warm.




THE

ART OF GLASS-BLOWING.

III.--_Fundamental Operations in Glass-Blowing_.


All the modifications of shape and size which can be given to tubes in
the construction of various instruments, are produced by a very small
number of dissimilar operations. We have thought it best to unite
the description of these operations in one article, both to avoid
repetitions and to place those who are desirous to exercise this art
in a state to proceed, without embarrassment, to the construction of
any instrument of which they may be provided with a model or a drawing;
for those who attend properly to the instructions given here, with
respect to the fundamental operations of glass-blowing, will need no
other instructions to enable them to succeed in the construction of all
kinds of instruments capable of being made of tubes. These fundamental
operations can be reduced to ten, which may be named as follows:--

  1. Cutting.
  2. Bordering.
  3. Widening.
  4. Drawing out.
  5. Choking.
  6. Sealing.
  7. Blowing.
  8. Piercing.
  9. Bending.
  10. Soldering.

We proceed to give a detailed account of these different operations.


1.--CUTTING.

The different methods of cutting of glass tubes which have been
contrived, are all founded on two principles; one of these is the
division of the surface of glass by cutting instruments, the other the
effecting of the same object by a sudden change of temperature; and
sometimes these two principles are combined in one process.

The first method consists in notching the tube, at the point where it
is to be divided, with the edge of a file, or of a thin plate of hard
steel, or with a diamond; after which, you press upon the two ends of
the tube, as if to enlarge the notch, or, what is better, you give the
tube a slight smart blow. This method is sufficient for the breaking
of small tubes. Many glass-blowers habitually employ an agate, or a
common flint, which they hold in one hand, while with the other they
rub the tube over the sharp edge of the stone, taking the precaution
of securing the tube by the help of the thumb. For tubes of a greater
diameter, you can employ a fine iron wire stretched in a bow, or, still
better, the glass-cutters' wheel; with either of these, assisted by a
mixture of emery and water, you can cut a circular trace round a large
tube, and then divide it with ease.

When the portion which is to be removed from a tube is so small that
you cannot easily lay hold of it, you cut a notch with a file, and
expose the notch to the point of the blowpipe flame: the cut then flies
round the tube.

This brings us to the second method of cutting tubes--a method which
has been modified in a great variety of ways. It is founded on the
property possessed by vitrified matters, of breaking when exposed to a
sudden change of temperature. Acting upon this principle, some artists
apply to the tube, at the point where they desire to cut it, a band
of fused glass. If the tube does not immediately separate into two
pieces, they give it a slight smart blow on the extremity, or they drop
a little water on the heated ring. Other glass-blowers make use of a
piece of iron heated to redness, an angle or a corner of which they
apply to the tube at the point where it is to be cut, and then, if the
fracture is not at once effected by the action of the hot iron, they
plunge the tube suddenly into cold water.

The two methods here described can be combined. After having made a
notch with a file, or the edge of a flint, you introduce into it a
little water, and bring close upon it the point of a very little tube
previously heated to the melting point. This double application of heat
and moisture obliges the notch to fly right round the tube.

When the object to be cut has a large diameter, and very thin
sides--when it is such a vessel as a drinking-glass, a cup, or a gas
tube--you may divide it with much neatness by proceeding as follows.
After having well cleaned the vessel, both within and without, pour
oil into it till it rises to the point, or very nearly to the point,
where you desire to cut it. Place the vessel, so prepared, in an airy
situation; then take a rod of iron, of about an inch in diameter, make
the extremity brightly red-hot, and plunge it into the vessel until the
extremity of the iron is half an inch below the surface of the oil:
there is immediately formed a great quantity of very hot oil, which
assembles in a thin stratum at the surface of the cold oil, and forms
a circular crack where it touches the sides of the glass. If you take
care to place the object in a horizontal position, and to plunge the
hot iron without communicating much agitation to the oil, the parts
so separated will be as neat and as uniform as you could desire them
to be. By means of this method we have always perfectly succeeded in
cutting very regular zones from ordinary glass.

The method which is described in some works, of cutting a tube by
twisting round it a thread saturated with oil of turpentine, and then
inflaming the thread, we have found to be unfit for objects which have
thick sides.

Some persons employ cotton wicks dipped in sulphur. By the burning of
these, the glass is strongly heated in a given line, or very narrow
space, which is instantly cooled by a wet feather or a wet stick. So
soon as a crack is produced, it can be led in any required direction
by a red-hot iron, or an inflamed piece of charcoal.

Finally, you may cut small portions from glass tubes in a state of
fusion, by means of common scissars.


2.--BORDERING.

To whatever use you may destine the tubes which you cut, they ought,
almost always, to be bordered. If you merely desire that the edges
shall not be sharp, you can smoothen them with the file, or, what is
better, you can expose them to the flame of the lamp until they are
rounded. If you fear the sinking in of the edges when they are in a
softened state, you can hinder this by working in the interior of the
tube a round rod of iron, such as pl. 1, fig. 5. The rod of iron should
be one-sixth of an inch thick; one end of it should be filed to a
conical point, and the other end be inserted into a thin, round, wooden
handle. You will find it convenient to have a similar rod with a slight
bend in the middle.

When you desire to make the edges of the tube project, bring the end
to a soft state, then insert in it a metallic rod, and move it about
in such a manner as to widen a little the opening. While the end of
the tube is still soft, place it suddenly upon a horizontal surface,
or press it by means of a very flat metallic plate. The object of
this operation is to make the end of the tube flat and uniform. The
metallic rod which you employ may be the same as we have described
in the preceding paragraph. Instead of agitating the rod in the tube,
you may hold it in a fixed oblique position, and turn the tube round
with the other hand, taking care to press it continually and regularly
against the rod. See pl. 1, fig. 6. Very small tubes can be bordered
by approaching their extremities to a flame not acted upon by the
blowpipe; particularly the flame of a spirit-lamp.

When the edges of a tube are to be rendered capable of suffering
considerable pressure, you can very considerably augment their
strength by soldering a rib or string of glass all round the end of
the tube--see pl. 1, fig. 12. Holding the tube in the left hand, and
the string of glass in the right, you expose them both at once to the
flame. When their extremities are sufficiently softened, you attach
the end of the rib of glass to the tube at a very short distance from
its extremity; you then continue gradually to turn the tube, so as to
cause the rib of glass to adhere to it, in proportion as it becomes
softened. When the rib has made the entire circumference of the tube,
you separate the surplus by suddenly darting a strong jet of fire upon
the point where it should be divided; and you continue to expose the
tube to the flame, always turning it round, until the ring of glass
is fully incorporated with the glass it was applied to. You then
remove the instrument from the flame, taking care to anneal it in so
doing. During this operation you must take care to prevent the sinking
together of the sides of the tube, by now and then turning the iron
rod in its interior. It is a _red heat_, or a _brownish red heat_, that
is best adapted to this operation.


3.--WIDENING.

When you desire to enlarge the diameter of the end of a tube, it is
necessary, after having brought it to a soft state, to remove it from
the flame, and to press the sides of the glass outwards by means of
a large rod of iron with a conical point. The tube must be again
heated, and again pressed with the conical iron rod, until the proper
enlargement is effected. This operation is much the same as that of
bordering a tube with projecting edges.


4.--DRAWING OUT.

You can _draw out_ or _contract_ a tube either in the middle or at the
end. Let us in the first place consider that a tube is to be drawn out
in the middle. If the tube is long, you support it with the right hand
_below_, and the left hand _above_, by which means you secure the force
that is necessary, as well as the position which is commodious, for
turning it continually and uniformly in the flame. It must be kept in
the jet till it has acquired a _cherry red heat_. You then remove it
from the flame, and always continuing gently to turn it, you gradually
separate the hands from each other, and draw the tube in a straight
line. In this manner you produce a long thin tube in the centre of
the original tube, which ought to exhibit two uniform cones where it
joins the thin tube, and to have the points of these cones in the
prolongation of the axis of the tube. See pl. 1, fig. 3.

To draw out a tube at its extremity, you heat the extremity till it is
in fusion, and then remove it from the flame; you immediately seize
this extremity with the pliers, and at the same time separate the two
hands. The more rapidly this operation is performed, the glass being
supposed to be well softened, the more capillary will the drawn-out
point of the tube be rendered. Instead of pinching the fused end with
the pliers, it is simpler to bring to it the end of a little auxiliary
tube, which should be previously heated, to fuse the two together, and
then to draw out the end of the original tube by means of the auxiliary
tube--see pl. 1, fig. 4 and 11. In all cases, the smaller the portion
of tube softened, the more abrupt is the part drawn out.

When you desire to draw out a point from the side of a tube, you must
heat that portion alone, by holding it fixedly at the extremity of the
jet of flame. When it is sufficiently softened, solder to it the end of
an auxiliary tube, and then draw it out. Pl. 1, fig. 18, exhibits an
example of a tube drawn out laterally. A _red heat_, or a _cherry red
heat_, is best adapted to this operation.


5.--CHOKING.

We do not mean by _choking_, the closing or stopping of the tube, but
simply a diminution of the interior passage, or bore. It is a sort of
contraction. For examples, see pl. 2, fig. 15, 20, 29. You perform the
operation by presenting to the flame a zone of the tube at the point
where the contraction is to be effected. When the glass is softened,
you draw out the tube, or push it together, according as you desire to
produce a hollow in the surface of the tube, or to have the surface
even, or to cause a ridge to rise above it. A _cherry red heat_ is the
proper temperature to employ.


6.--SEALING.

If the sides of the tube to be sealed are thin, and its diameter is
small, it is sufficient to expose the end that you wish to close to
the flame of the lamp. When the glass is softened it sinks of itself,
in consequence of the rotatory motion given to it, towards the axis
of the tube, and becomes rounded. The application of no instrument is
necessary.

If the tube is of considerable diameter, or if the sides are thick, you
must soften the end, and then, with a metallic rod or a flat pair of
pliers, mould the sides to a hemisphere, by bringing the circumference
towards the centre, and continuing to turn the tube in the flame, until
the extremity is well sealed, and perfectly round. Examples of the
figure are to be seen in pl. 2, fig. 3 and 5. Instead of this method,
it is good, when the extremity is sufficiently softened, to employ an
auxiliary tube, with the help of which you can abruptly draw out the
point of the original tube, which becomes by that means cut and closed
by the flame. In order that this part may be well rounded, you may,
as soon as the tube is sealed, close the other extremity with a little
wax, and continue to expose the sealed part to the flame, until it has
assumed the form of a _drop of tallow_. See pl. 2, fig. 15. You can
also seal in this fashion, by blowing, with precaution, in the open end
of the tube, while the sealed end is in a softened state.

If you desire the sealed part to be flat, like pl. 3, fig. 30, you
must press it, while it is soft, against a flat substance. If you wish
it to be concave, like the bottom of a bottle, or pl. 3, fig. 2, you
must suck air from the tube with the mouth; or, instead of that, force
the softened end inwards with a metallic rod. You may also draw out
the end till it be conical, as pl. 2, fig. 4, or terminate it with a
little button, as pl. 2, fig. 6. In some cases the sealed end is bent
laterally; in others it is twirled into a ring, having previously been
drawn out and stopped in the bore. In short, the form given to the
sealed end of a tube can be modified in an infinity of ways, according
to the object for which the tube may be destined.

You should take care not to accumulate too much glass at the place
of sealing. If you allow it to be too thick there, you run the risk
of seeing it crack during the cooling. Some farther observations on
sealing will be found at the article _Water Hammer_, in a subsequent
section. The operation of sealing succeeds best at a _cherry-red heat_.


7.--BLOWING.

The construction of a great number of philosophical instruments
requires that he who would make them should exercise himself in the art
of blowing _bulbs_ possessing a figure exactly spherical. This is one
of the most difficult operations.

To blow a bulb at the extremity of a tube, you commence by sealing it;
after which, you collect at the sealed extremity more or less glass,
according to the size and the solidity which you desire to give to
the bulb. When the end of the tube is made thick, completely sealed,
and well rounded, you elevate the temperature to a _reddish white_
heat, taking care to turn the tube continually and rapidly between
your fingers. When the end is perfectly soft you remove it from the
flame, and, holding the tube horizontally, you blow quickly with the
mouth into the open end, without discontinuing for a single moment the
movement of rotation. If the bulb does not by this operation acquire
the necessary size, you soften it again in the flame, while under the
action of which you turn it very rapidly, lest it should sink together
at the sides, and become deformed. When it is sufficiently softened you
introduce, in the same manner as before, a fresh quantity of air. It
is of importance to observe that, if the tube be of a large diameter,
it is necessary to contract the end by which you are to blow, in order
that it may be turned round with facility while in the mouth.

When the bulb which you desire to make is to be somewhat large, it is
necessary, after having sealed the tube, to soften it for the space of
about half an inch from its extremity, and then, with the aid of a
flat piece of metal, to press moderately and repeatedly on the softened
portion, until the sides of the tube which are thus pressed upon,
sink together, and acquire a certain degree of thickness. During this
operation, however, you must take care to blow, now and then, into the
tube, in order to retain a hollow space in the midst of the little mass
of glass, and to hinder the bore of the tube from being closed up. When
you have thus, at the expense of the length of the tube, accumulated
at its extremity a quantity of glass sufficient to produce a bulb, you
have nothing more to do than to heat the matter till it is raised to a
temperature marked by a _reddish-white_ colour, and then to expand it
by blowing.

Instead of accumulating the glass thus, it is more expedient to blow on
the tube a series of little bulbs close to one another (see pl. 1, fig.
8), and then, by heating the intervals, and blowing, to unite these
little bulbs into a large one of convenient dimensions.

We have already observed, and we repeat here, that it is indispensably
necessary to hold the glass _out_ of the flame during the act
of blowing. This is the only means of maintaining uniformity of
temperature in the whole softened parts of the tube, without which it
is impossible to produce bulbs with sides of equal thickness in all
their extent.

When you desire to form a bulb at the extremity of a capillary tube,
that is to say, of a tube which has a bore of very small diameter,
such as the tubes which are commonly employed to form thermometers,
it would be improper to blow it with the mouth; were you to do so,
the vapour which would be introduced, having a great affinity for the
glass, would soon obstruct the little canal, and present to the passage
of the air a resistance, which, with the tubes of smallest interior
diameter, would often be insurmountable. But, even when the tubes you
employ have not so very small an internal diameter, you should still
take care to avoid blowing with the mouth; because the introduction of
moisture always injures fine instruments, and it is impossible to dry
the interior of a capillary tube when once it has become wet. It is
better to make use of a bottle of Indian rubber, which can be fixed on
the open end of the tube by means of a cork with a hole bored through
it. You press the bottle in the hand, taking care to hold the tube
vertically, with the hot part _upwards_; if you were not to take this
precaution, the bulb would be turned on one side, or would exhibit the
form of a pear, because it is impossible, in this case, to give to the
mass in fusion that rotatory motion which is necessary, when the tube
is held horizontally, to the production of a globe perfectly spherical
in its form, and with sides of equal thickness.

Whenever you blow into a tube you should keep the eye fixed on the
dilating bulb, in order to be able to arrest the passage of air at the
proper moment. If you were not to attend to this, you would run the
risk of giving to the bulb too great an extension, by which the sides
would be rendered so thin that it would be liable to be broken by the
touch of the lightest bodies. This is the reason that, when you desire
to obtain a large bulb, it is necessary to thicken the extremity of the
tube, or to combine many small bulbs in one, that it may possess more
solidity.

In general, when you blow a bulb with the mouth, it is better to
introduce the air a little at a time, forcing in the small portions
very rapidly one after the other; rather than to attempt to produce the
whole expansion of the bulb at once: you are then more certain of being
able to arrest the blowing at the proper time.

When you desire to produce a moderate expansion, either at the
extremity or in any other part of a tube, you are enabled easily to
effect it by the following process, which is founded on the property
possessed by all bodies, and especially by fluids, of expanding when
heated; a property which characterises air in a very high degree. After
having sealed one end of the tube and drawn out the other, allow it
to become cold, in order that it may be quite filled with air; close
the end which has been drawn out, and prevent the air within the tube
from communicating with that at its exterior; then gradually heat the
part which you desire to have expanded, by turning it gently in the
flame of a lamp. In a short time the softened matter is acted on by the
tension of the air which is enclosed and heated in the interior of the
tube; the glass expands, and produces a bulb or swelling more or less
extensive, according as you expose the glass to a greater or lesser
degree of heat.

To blow a bulb in the middle of a tube, it is sufficient to seal it at
one of its extremities, to heat the part that you wish to inflate, and,
when it is at a _cherry-red_ heat, to blow in the tube, which must be
held horizontally and turned with both hands, of which, for the sake of
greater facility, the left may be held above and the right below.

If the bulb is to be large, the matter must previously be thickened
or accumulated, or, instead of that, a series of small bulbs first
produced, and these subsequently blown into a single larger bulb, as we
have already mentioned. See pl. 1, fig. 8.

For some instruments, the tubes of which must be capillary, it is
necessary to blow the bulbs separately, and then to solder them to
the requisite adjuncts. The reason of this is, that it would be too
difficult to produce, from a very fine tube, a bulb of sufficient size
and solidity to answer the intended purpose.

You make choice of a tube which is not capillary, but of a sufficient
diameter, very cylindrical, with equal sides, and tolerably
substantial: it may generally be from the twentieth to the twelfth of
an inch thick in the glass. You soften two zones in this tube, more
or less near to each other, according to the bulk you desire to give
to the bulb, and you draw out the melted part in points. The talent
consists in _well-centering_--that is to say, in drawing out the melted
tube in such a manner that the thin parts or points shall be situated
exactly in the prolongation of the axis of the little portion of the
original tube remaining between them. This operation is technically
termed drawing _a cylinder between two points_. The tube so drawn out
is exhibited by pl. 1, fig. 4. You cut these points at some distance
from the central or thick part, and seal one end; you next completely
soften the little thick tube and expand it into a bulb, by blowing
with the precautions which have already been described. You must keep
the glass in continual motion, if you desire to be successful in this
experiment. Much rapidity of movement, and at the same time lightness
of touch, are requisite in the operation here described. It is termed
_blowing a bulb between two points_. Pl. 1, fig. 10, exhibits a bulb
blown between two points.

To obtain a _round_ bulb, you should hold the tube horizontally; to
obtain a _flattened_ bulb, you should hold it perpendicularly, with
the fused extremity turned above; to obtain a _pear-shaped_ bulb, you
should hold the fused extremity downwards.

When you are working upon a bulb between two points, or in the middle
of a tube, you should hold the tube horizontally, in the ordinary
manner; but you are to push the softened portion together, or to draw
it out, according as you desire to produce a ridge or a prolongation.

When you are at liberty to choose the point from which you are to blow,
you should prefer, 1st, that where the moisture of the breath can be
the least prejudicial to the instrument which is to be made; 2dly, that
which brings the part which is to be expanded nearest to your eye;
3dly, that which presents the fewest difficulties in the execution.
When bulbs are to be formed in complicated apparatus, it is good to
reflect a little on the best means of effecting the object. It is easy
to understand that contrivances which may appear very simple on paper,
present difficulties in the practical execution which often call for
considerable management.


8.--PIERCING.

You first seal the tube at one extremity, and then direct the point of
the flame on the part which you desire to pierce. When the tube has
acquired a _reddish-white_ heat, you suddenly remove it from the flame,
and forcibly blow into it. The softened portion of the tube gives way
before the pressure of the air, and bursts into a hole. You expose the
tube again to the flame, and border the edges of the hole.

It is scarcely necessary to observe, that, if it be a sealed extremity
which you desire to pierce, it is necessary to turn the tube between
the fingers while in the fire; but if, on the contrary, you desire to
pierce a hole in the side of a tube, you should keep the glass in a
fixed position, and direct the jet upon a single point.

If the side of the tube is thin, you may dispense with blowing. The
tube is sealed and allowed to cool; then, accurately closing the open
extremity with the finger, or a little wax, you expose to the jet the
part which you desire to have pierced. When the glass is sufficiently
softened, the air enclosed in the tube being expanded by the heat,
and not finding at the softened part a sufficient resistance, bursts
through the tube, and thus pierces a hole.

You may generally dispense with the sealing of the tube, by closing the
ends with wax, or with the fingers.

There is still another method of performing this operation, which is
very expeditious, and constantly succeeds with objects which have thin
sides. You raise to a _reddish white_ heat a little cylinder of glass,
of the diameter of the hole that you desire to make, and you instantly
apply it to the tube or globe, to which it will strongly adhere. You
allow the whole to cool, and then give the auxiliary cylinder a sharp
slight knock; the little cylinder drops off, and carries with it the
portion of the tube to which it had adhered. On presenting the hole to
a slight degree of heat, you remove the sharpness of its edges.

When you purpose to pierce a tube laterally, for the purpose of joining
to it another tube, it is always best to pierce it by blowing many
times, and only a little at a time, and with that view, to soften the
glass but moderately. By this means the tube preserves more thickness,
and is in a better state to support the subsequent operation of
soldering.

There are circumstances in which you can pierce tubes by forcibly
sucking the air out of them; and this method sometimes presents
advantages that can be turned to good account. Finally, the orifices
which are produced by cutting off the lateral point of a tube drawn out
at the side, may also be reckoned as an operation belonging to this
article.


9.--BENDING.

If the tube is narrow, and the sides are pretty thick, this operation
presents no difficulty. You heat the tube, but not too much, lest it
become deformed; a _reddish-brown_ heat is sufficient, for at that
temperature it gives way to the slightest effort you make to bend it.
You should, as much as possible, avoid making the bend too abrupt. For
this purpose, you heat a zone of one or two inches in extent at once,
by moving the tube backwards and forwards in the flame, and you take
care to bend it very gradually.

But if the tube is large, or its sides are thin, and you bend it
without proper precautions, the force you employ entirely destroys
its cylindrical form, and the bent part exhibits nothing but a double
flattening,--a canal, more or less compressed. To avoid this deformity
it is necessary, first, to seal the tube at one extremity, and then,
while giving it a certain curvature, to blow cautiously by the other
extremity, which for convenience sake should previously be drawn out.
When tubes have been deformed by bad bending, as above described, you
may, by following this method, correct the fault; that is to say, upon
sealing one extremity of the deformed tube, heating the flattened
part, and blowing into the other extremity, you can with care reproduce
the round form.

In general, that a curvature may be well-made, it is necessary that
the side of the tube which is to form the concave part be sufficiently
softened by heat to sink of itself equally in every part during the
operation, while the other side be only softened to such a degree as
to enable it to give way under the force applied to bend it. On this
account, after having softened in a _cherry-red heat_ one side of the
tube, you should turn the other side, which is to form the exterior of
the curvature, towards you, and then, exposing it to the point of the
jet, you should bend the tube immediately upon its beginning to sink
under the heat.

When you desire to bend the extremity of a tube into a ring you must
employ a metallic rod, with which, by pressing on the tube, you
separate with a curve, C, (see pl. 1, fig. 14) all the portion A C
which is necessary to produce the desired curl. You then successively
soften all parts of this curve, and gradually twist it in the direction
indicated by the arrow, pressing the iron rod constantly upon the
extremity of the curve. When the end A comes into contact with bend C
you solder them together at this point, and thus complete the ring. Pl.
2, fig. 27, and pl. 3, fig. 27, exhibit examples of rings formed by
this process.


10.--SOLDERING.

If the tubes which you propose to solder are of a small diameter,
pretty equal in size, and have thick sides, it is sufficient, before
joining them together, to widen them equally at their extremities, by
agitating a metallic rod within them. (Pl. 1, fig. 17.)

But if they have thin sides, or are of a large diameter, the bringing
of their sides into juxta-position is very difficult, and the method
of soldering just indicated becomes insufficient. In this case you are
obliged to seal, and subsequently to pierce, the two ends which you
desire to join. The disposition which this operation gives to their
sides very much facilitates the soldering.

Finally, when the tubes are of a very different diameter, you must draw
out the extremity of the larger and cut it where the part drawn out
corresponds in diameter to the tube which it is to be joined to. Pl. 1,
fig. 9 and 15, exhibit examples of this mode of adapting tubes to one
another.

For lateral solderings you must dispose the tubes in such a manner that
the sides of the orifices which you desire to join together coincide
with each other completely. See pl. 1, fig. 7.

When the holes are well prepared, you heat at the same time the two
parts that are to be soldered together, and join them at the moment
when they enter into fusion. You must push them slightly together, and
continue to heat successively all their points of contact; whereupon
the two tubes soon unite perfectly. As it is almost always necessary,
when you desire the soldering to be neatly done, or the joint to be
imperceptible, to terminate the operation by blowing, it is proper to
prepare the extreme ends of the tubes before-hand. That end of the tube
by which you intend to blow should be carefully drawn out, provided it
be so large as to render drawing out necessary; and the other end of
the tube, if large, should be closed with wax, as in pl. 1, fig. 9,
or if small, should be sealed at the lamp (pl. 1, fig. 15). When the
points of junction are perfectly softened, and completely incorporated
with each other, you introduce a little air into the tube, which
produces a swelling at the joint. As soon as this has taken place,
you must gently pull the two ends of the joined tube in different
directions, by which means the swelled portion at the joint is brought
down to the size of the other parts of the tube, so that the whole
surface becomes continuous. The soldering is then finished.

To solder a bulb or a cylinder between two points, to the extremity
of a capillary tube, you cut and seal one of the points at a short
distance from the bulb (pl. 1, fig. 16), and at the moment when this
extremity is in fusion you pierce it by blowing strongly at the other
extremity. By this means the opening of the reservoir is terminated
by edges very much widened, which facilitates considerably its being
brought into juxta-position with the little tube. In order that the
ends of the two tubes may be well incorporated the one with the
other, you should keep the soldered joint for some time in the flame,
and ought to blow in the tube, push the ends together and draw them
asunder, until the protuberance is no longer perceptible.

If, after having joined two tubes, it should be found that there still
exists an opening too considerable to be closed by simply pushing the
two tubes upon one another, you can close such an opening by means of
a morsel of glass, applied by presenting the fused end of an auxiliary
tube.

You should avoid soldering together two different species of glass--for
example, a tube of ordinary glass with a tube of flint-glass; because
these two species of glass experience a different degree of contraction
upon cooling, and, if joined together while in a fused state, are
so violently pulled from one another as they become cool, that the
cohesion of the point of soldering is infallibly overcome, and the
tube breaks. You ought also, for a similar reason, to take care not to
accumulate a greater mass of glass in one place than in another.

If the first operation has not been sufficient to complete the
soldering, the tube must be again presented to the flame, and again
pushed together at the joint, or drawn asunder, or blown into,
according as it may appear to be necessary. In all cases the soldering
is not truly solid, but inasmuch as the two masses of glass are well
incorporated together, and present a surface continuous in all points.

The mineralogical flame (pl. 1, fig. 1, A´ B) is that which is to be
employed in preference to the larger flame, when you desire to effect a
good joining: it is sufficient to proportion the size of the flame to
the object you wish to execute.




THE

ART OF GLASS-BLOWING.

IV.--_Construction of Chemical and Philosophical Instruments._


When a person is well acquainted with the fundamental operations which
we have just described, the preparation of the instruments of which we
are about to speak can present scarcely any difficulty. Indeed, some of
them are so extremely simple, and are so easy of execution, that it is
sufficient to cast a glance upon the figures which represent them, to
seize at once the method which must be followed in their construction.
Of such instruments we shall not stop to give a detailed description,
but shall content ourselves with presenting the design.

On the other hand, it is of importance to observe that a certain
number of instruments are _graduated_ or furnished with pieces, or
_mountings_, of which it is not the object of our art to teach the
construction, and which demand a more or less extensive knowledge
of the sciences. We shall treat of these mountings but summarily,
referring the student, for more detailed instructions, to the works
on natural philosophy and chemistry, in which these instruments are
especially treated of. Our reason for this is, that we do not wish
to abandon the plan we had adopted of describing simply the art of
glass-blowing. To describe the use and application of philosophical
instruments, or to explain the principles on which they act, would be
passing quite out of our province.

ADAPTERS.--These are tubes of glass of various forms, employed in
chemistry to connect together the different pieces constituting an
apparatus--as, for example, to join a retort to a receiver during
the operation of distillation. You should take care to border the
extremities of an adapter; or you may widen them into the form of the
mouth of a bottle, when they are to be closed air-tight by corks.
Besides this, there is nothing particular to be observed in the
preparation of adapters.

       *       *       *       *       *

APPARATUS FOR BOILING IN VACUO.--Represented by pl. 3, fig. 19. Employ
a tube about a quarter of an inch in diameter. Blow two bulbs; give the
tube the necessary curvature; fill one of the bulbs with nitric ether;
boil the ether to expel the atmospheric air from the apparatus, then
seal the opening in the other bulb.

       *       *       *       *       *

APPARATUS FOR FREEZING IN VACUO. _The Cryophorus._--Take a tube
one-third of an inch or rather more in diameter, and pretty thick in
the sides. Blow a bulb at each end; the first at the sealed part of the
tube, the other at the open point; then give to the tube the curvature
represented by pl. 3, fig. 32. Introduce as much water as will half
fill one of the bulbs; make the water boil, and draw off the point and
seal the apparatus during the ebullition.

       *       *       *       *       *

APPARATUS FOR CONDUCTING WATER IN BENT TUBES.--Solder a funnel (see
FUNNELS) to the end of a tube; pierce two holes in this tube in the
same line, and solder to each a little addition proper to receive a
cork. Finish the instrument by bending it in the manner indicated by
pl. 4, fig. 18.

       *       *       *       *       *

APPARATUS FOR EXPERIMENTS ON RUNNING LIQUIDS.--A tube bent once at a
right angle, mounted with a funnel, pierced laterally, and soldered at
the same point to a smaller tube. See pl. 3, fig. 17.

       *       *       *       *       *

APPARATUS FOR EXHIBITING THE PHENOMENA OF CAPILLARY TUBES.--This
apparatus consists of a capillary tube soldered to another tube of a
more considerable diameter. Sometimes it is bent like the letter U. Pl.
3, fig. 15.

       *       *       *       *       *

APPARATUS FOR THE PREPARATION OF PHOSPHURET OF LIME.--An apparatus that
can be employed for the preparation of phosphuret of lime, as well as
in a variety of other chemical experiments, consists of a tube sealed
at one extremity, slightly bent and choked at two inches and a half
from the sealed part, and drawn out (after the introduction of the
substances to be operated upon) at the other extremity. This little
distillatory apparatus is represented by pl. 3, fig. 29.

       *       *       *       *       *

ARCHIMEDES’S SCREW.--There is no particular process for the making of
this instrument. It is, however, necessary for one who would succeed in
making it, to exercise himself in the art of well bending a tube. After
a few attempts, you may finish by producing a pretty-regular spiral.
The tube chosen for this instrument should be six or seven feet long,
and about one-third of an inch in diameter. You commence by making
a bend, nearly at a right angle, about four inches from one of its
extremities. This bent portion serves afterwards as a handle, and very
much facilitates the operation; it represents the prolongation of the
rational axis which may be conceived to pass through the centre of the
spiral. See pl. 4, fig. 10.

       *       *       *       *       *

BARKER’S MILL.--_Apparatus for exhibiting the rotatory motion produced
by the running of liquids._--Contract a tube at its two extremities,
pierce it laterally about the middle of its length, and solder to the
hole an additional tube, terminated by a funnel. Soften the principal
tube at the side opposite to the part that was pierced, and form there
a conical cavity by pressing the softened glass inward with the aid
of a metallic rod. This cavity must be so carefully made that the
whole apparatus can be supported on a pivot. Bend the contracted ends
of the tube horizontally, and in different directions, cut off their
extremities at a proper length, and slightly border the edges of the
orifices. See pl. 3, fig. 33.

You may produce this apparatus under a different form, as may be seen
at pl. 3, fig. 5.

       *       *       *       *       *

BAROMETERS.--Barometers serve to measure the pressure of the
atmosphere. The following are the varieties most in use.

       *       *       *       *       *

CISTERN BAROMETER.--Take a tube about thirty-two inches long, and at
least one-third of an inch in diameter, internally; seal one of its
extremities, free it with most particular care from moisture, fill
it with mercury, and make the mercury boil in the tube, by heat, in
order to drive out every particle of air which might be present. When
the tube is full of mercury, and the boiling has taken place, turn it
upside down, and plunge the open end into a cistern also filled with
mercury which has been boiled. See pl. 2, fig. 4.

       *       *       *       *       *

DIAL (or WHEEL) BAROMETER.--The tube intended for this barometer should
be very regular in the bore. It should be thirty-nine inches long.
Close it at one end, and bend it like the letter U at about thirty-two
inches from the sealed extremity. See pl. 2, fig. 5, and _Graduation of
the Dial Barometer_.

SYPHON BAROMETER.--Make use of such a tube as might be employed
for a _Cistern Barometer_; solder to its open end a cylindrical or
spherical reservoir, and bend the tube close to the point of junction
in such a manner as to bring the cylinder parallel with the tube.
If the reservoir is to be closed with a cover of leather, cut off
the remaining point of the cylinder, slightly widen the orifice, and
then border it. If no leather is to be applied, but the point of the
cylinder left open, it is necessary, after the introduction of the
mercury, to draw off the point abruptly, and to leave an opening so
small that mercury cannot pass by it. Pl. 2, fig. 6.

       *       *       *       *       *

STOP-COCK BAROMETER.--This differs from the preceding barometer only by
having a stop-cock mounted in iron between the reservoir and the tube.

       *       *       *       *       *

COMPOUND BAROMETERS.--Blow a bulb at each end of a barometer tube
of about thirty-three inches in length. Solder a small and almost
capillary tube to the point which terminates one of the bulbs, and bend
the great tube very near this bulb. This must be done in such a manner
that the centre of one bulb shall be thirty inches from the centre of
the other bulb. Introduce a quantity of mercury sufficient to fill the
great tube and half the two bulbs; fill the remaining space in the last
bulb with alcohol.

You may give a different disposition to this instrument. Divide a
barometer tube into two, three, or four pieces, and reunite the pieces
by intermediate capillary tubes, so as to form a series of large and
small tubes, soldered alternately the one at the end of the other. Then
communicate to this compound tube the form exhibited by pl. 3, fig. 25,
and join, at each superior bend, a little tube, for the convenience of
easily filling the instrument with mercury: seal these tubes as soon
as the mercury is introduced. The graduation of compound barometers is
made by bringing them into comparison with a good standard barometer.
After taking two or three fixed points, it is easy to continue the
scale.

       *       *       *       *       *

GAY LUSSAC’S BAROMETER.--Take a tube which is very regular in the bore,
four-tenths of an inch in diameter, and thirty-five inches and a half
in length. Seal one of its extremities and draw out the other; then
cut the tube at about two-thirds of its whole length from the sealed
end, and reunite the two pieces by means of a capillary tube soldered
between them, the whole being kept in a line. See pl. 2, fig. 1. Pierce
laterally the part of the tube which is drawn out, at some inches
from the base of the point, and force the margin of the hole into the
interior of the tube, by means of a conical point of metal, in such a
manner as to form a little sunk funnel, of which the orifice must be
very small. After having introduced the proper quantity of mercury into
the instrument, boil it, and assist the disengagement of the bubbles
of air by agitating a fine iron wire within the tube. Then remove the
part of the tube which was drawn out, by sealing the end of the wide
part. Give to the whole instrument the curvature indicated by pl. 2,
fig. 3.

       *       *       *       *       *

BUNTEN’S BAROMETER.--This instrument differs from the preceding but in
one point, namely, that the capillary tube is formed of two soldered
pieces, of which the one, passing into the other, is terminated by a
capillary point. This arrangement is exhibited by pl. 2, fig. 2.

       *       *       *       *       *

BAROMETER PIERCED LATERALLY FOR DEMONSTRATIONS.--Take a tube
thirty-nine inches long, with thick sides, and two-tenths of an inch
internal diameter. Seal it at one end, and choke it at the distance
of eight inches therefrom. Pierce a hole in the tube about twelve
or sixteen inches from the choked part, and solder to the hole an
additional piece, which can be closed by a cork or covered by a piece
of bladder. The instrument is represented by pl. 2, fig. 15.

       *       *       *       *       *

BELL-GLASSES FOR EXPERIMENTS.--These are pieces of tube sealed at one
end, and widened or bordered at the other. They are extremely useful,
and much employed in chemical experiments. They also supply the place
of bottles for preserving small quantities of substances. Sometimes
they are required to be straight, as pl. 3, fig. 12. Sometimes they
need to be curved, as pl. 3, fig. 29. This is particularly the case
when they are to be employed as retorts, for which purpose the sealed
part should be made thin. Pl. 3, fig. 6, exhibits a retort with a
tubulure.

       *       *       *       *       *

BLOWPIPE.--We shall give in this article an account of the various
pieces of glass which form part of the blowpipe described in the early
part of this work. See pl. 1, fig. 19.

The beak C, which is employed with the candlestick, is merely a bent
tube, at the extremity of which a bulb is blown. The bulb is terminated
by a point, the thickness of the sides of which is augmented by turning
it for a long time in the flame.

As for the beak used with the lamp, it is simply a bent tube C´, of
which the orifice has been diminished by turning it round in the flame.
The point of this beak is not drawn out like that of the beak described
in the preceding paragraph, but is allowed to be thick, that it may not
melt in the flame of the lamp.

The tube D F has four-tenths of an inch internal diameter, and is
pretty thick in the sides. You must commence by bordering and slightly
widening one of its extremities, and then proceed to choke it at about
two inches from its other extremity, taking care to give to the choked
part a figure as perfectly conical as possible, in order that the valve
may act well. We have described the valve at length at p. 6.

The tube _d_ is as much narrower than the tube D F as is necessary
to permit it to pass up and down within the latter. Its use is to
lengthen or shorten the tube for the convenience of the blower. The
lower end is wound round with waxed thread, to make it fit air-tight.
The mouth-piece is executed by widening the end of the tube, and
then, while the widened part is still soft, by pressing the two sides
obliquely, one against the other. By this means you give to the
mouth-piece a flattened form, which adapts it better to the lips. The
tube is finished by slightly bending this extremity.

In order that the bladder, or air reservoir, may be conveniently and
securely attached to the tube E, you must take care to widen the end of
this tube, and to turn up the edges strongly, by pressing the soft end
against a flat metallic surface.

       *       *       *       *       *

CAPSULES.--These are very small mercury funnels, of which the opening
or neck has been closed. To transform these funnels into capsules, you
must cut the neck as close as possible, and then soften, close, and
flatten the opening. In performing this operation, hold the capsule by
the edge with your pincers, and employ a piece of metal to press the
glass together and make it close the hole and form the flat bottom of
the capsule. See pl. 2, fig. 23.

_Another Method._--After having blown a bulb at the end of a point,
soften a narrow zone of the bulb, and then blow suddenly and strongly
into it; by which means you separate the bulb into two capsules, which
only need to be bordered. If you find any difficulty in presenting
to the flame the capsule which forms the part of the bulb opposed to
the point, you can attach to it a little rod of glass, which you can
afterwards easily separate by a slight smart blow.

Occasionally you will have to make _capsules with double sides_, which
will be described at the article _Nicholson’s Hydrometer_.

       *       *       *       *       *

CARTESIAN DEVILS.--Blow a bulb at the extremity of a very small tube,
and heat a portion of the bulb, for the purpose of prolonging it into
a beak. This can be effected with the aid of an auxiliary tube, which,
on being joined to the heated part of the bulb, carries away with it
the portion of glass which adheres. This portion of the bulb becomes
thus prolonged into a little point, which must be cut at its extremity,
so as to leave a small opening. The principal tube must be cut at
the distance of half an inch from the bulb, and the ends of it must
be drawn out and twisted into a ring. Instead of forming laterally a
little beak to the bulb, you may pierce the tail, after twisting it
into the form of a ring, or you may manage in such a manner as not to
obliterate the canal of the twisted part. In general, little enamel
figures are suspended to the ring of these globes, as is represented
by pl. 2, fig. 22. A simple bulb, blown at the extremity of a small
portion of tube, can supply the place of the Ludion or Cartesian devil.
See pl. 2, fig. 8.

       *       *       *       *       *

COMMUNICATING VASES.--Employ a tube of a large diameter; terminate one
of its extremities with a funnel, fashion the other like the neck of a
bottle; and bend the tube into the shape shewn by pl. 4, fig. 11. Then
twist some other tubes into various forms, according to the end you
propose to attain, and adjust these tubes to the neck of the large tube
by means of corks, which have holes bored through them. In this manner
an exchange of tubes is provided for various experiments.

       *       *       *       *       *

DROPPING TUBES.--The name _dropping tube_ is given to an instrument
of glass which is very much employed in chemistry, for the purpose of
transferring small quantities of liquor from one vessel into another,
without disturbing either of the vessels. Dropping tubes are made of a
great variety of forms and sizes, according to the purposes to which
they are intended to be applied.

Blow a bulb between two points, and then, before the glass has regained
its consistence, lengthen the bulb into an oval form. Cut and border
the two points.

If the bulb, or reservoir, is to be so large that it cannot be formed
at the expense of the thickness of the tube, and yet be sufficiently
strong, it must be blown separately from a larger tube, and then
soldered to two smaller tubes, one of which should have a certain
curvature given to it. See pl. 2, fig. 20.

Sometimes a dropping tube is employed to measure small quantities of
liquid. In this case the point should be drawn off abruptly, and the
scale should be marked on the shank or tube with spots of black enamel.

Pl. 2, fig. 21, represents a peculiar variety of dropping tube employed
in some experiments. It is made in the same manner as the common
dropping tubes, excepting that, when the tail is formed, it is sealed
at the extremity, bent there into a ring, and then pierced at A.

Pl. 3, fig. 26, represents another variety of dropping tube, a
description of which is unnecessary.

       *       *       *       *       *

FOUNTAINS.--It will readily be understood by those acquainted with the
construction of hydraulic apparatus, that, by means of a judicious
arrangement of glass tubes, a great variety of fountains may be
produced. The following are given as examples.

       *       *       *       *       *

FOUNTAIN OF CIRCULATION.--Take a tube, twenty-four or thirty inches
long, nearly half an inch in diameter, and with pretty thick sides;
blow a bulb at one of its extremities, and bend the other into a U,
after having drawn it out as indicated by pl. 3, fig. 4. Pierce the
tube at B, and join there a short piece adapted to receive a cork. Then
prepare a bulb of the same size as the first bulb, and solder it to the
extremity of a very long and almost capillary tube, which you must
bend in zig-zag, in such a manner as to make it represent a Maltese
cross, a star, a rose, or any other figure that may be suggested. The
side of the bulb opposite to that which is attached to this twisted
tube, ought to be formed like the neck of a bottle, in order that it
may receive the drawn-out part of the larger tube, which should enter
the bulb until the point of the large tube nearly touches the neck of
the little tube at its junction with the bulb. This disposition is
shewn in the figure. Seal now the other end of the little tube to the
bulb of the large tube; then, with a little cement or sealing-wax,
close the space between the bulb of the little tube and the point of
the large tube. The instrument being thus prepared, as much alcohol,
previously coloured red, must be inserted by the neck _b_ as is
sufficient to fill one of the bulbs. The neck is then closed with a
cork, and a little cement or sealing-wax. Or, instead of forming this
neck to the instrument, the additional piece may be drawn out to a
point, which permits it to be sealed hermetically.

       *       *       *       *       *

FOUNTAIN OF COMPRESSION.--Introduce into a tube of large diameter a
piece of capillary tube with thick sides. This must pass a little
beyond the extremity of the large tube, which is to be softened and
soldered to the other, so that it shall be fixed concentrically. The
common point is then to be drawn out. When the tube is quite cold, and
the small tube properly fixed in the centre of the large one, cut the
latter at a proper distance, border it, and choke it near the end,
which must be fashioned in such a manner as to be capable of being
completely closed by a cork. See pl. 2, fig. 29.

       *       *       *       *       *

INTERMITTING FOUNTAIN.--This apparatus is represented by pl. 3, fig.
16. Solder a cylindrical reservoir to the extremity of a capillary
tube, pierced at _a_, and sealed at its extremity. Draw out abruptly
the point of the reservoir, and give it a very small orifice; then give
to the capillary tube the form indicated by the figure. Prepare next a
funnel resembling a mercury-funnel, but much larger; choke the neck of
this funnel, and bend the tube into the form of a syphon.

       *       *       *       *       *

HERO’S FOUNTAIN.--Solder a bulb to the extremity of a tube, and
transform the bulb into a funnel. Close the funnel with a cork, and
solder to the other end of the tube a bulb similar to the first. Next,
solder a third bulb between two tubes, of which one must be twice as
long the other; solder the longer of these tubes to the bulb of the
first tube, and draw out the point of the shorter tube. You have now a
long tube, with a funnel at one end, a contracted point at the other,
and two bulbs in its length. Give to the whole apparatus the form
indicated by pl. 3, fig. 21.

       *       *       *       *       *

FUNNELS.--It will be seen, upon looking over the engravings, that
funnels require to be made for a great variety of instruments; you
ought therefore to acquire as soon as possible the art of making them
well. The following are those most frequently required.

       *       *       *       *       *

RETORT FUNNEL.--Blow a bulb at the extremity of a tube; present
the superior hemisphere of the bulb to the flame, and when it is
sufficiently softened, blow strongly into the other end of the tube.
The air will force its way through the bulb, making a hole which will
be larger or smaller according to the extent of surface which may
have been softened. The opening of the funnel being made thus, there
is nothing more to do than to adjust the edges, which, in the present
state, are both fragile and irregular. This it is very easy to do.
The edges are softened, the most prominent parts are cut off with the
scissars, and the parts which are thin are bent back on themselves,
that they may become thicker. Upon turning the funnel round in the
flame, the smaller irregularities give way, and the edges become
rounded. See pl. 2, fig. 24.

When the funnel is desired to be very large in proportion to the size
of the tube, a bulb is made from a larger tube, and afterwards soldered
to the small tube, and transformed into a funnel in the manner above
described.

       *       *       *       *       *

FUNNEL FOR INTRODUCING MERCURY INTO NARROW TUBES.--The mercury-funnel
is represented by pl. 2, fig. 25. Blow a bulb between two points; cut
off one of the points, and open the bulb at that place, in the manner
described in the preceding article.

       *       *       *       *       *

HYDROSTATIC FUNNEL.--This is represented by pl. 3, fig. 31. It is an
instrument of constant use in chemical experiments. Form a funnel
at the extremity of a tube in the manner described above, having
previously blown a bulb near the middle of the tube. When this has been
done, bend the tube into the form shown by the figure.

       *       *       *       *       *

HOUR-GLASSES.--Blow four bulbs on a tube close to each other; open the
two end bulbs like funnels, and then form them into flat supports or
pedestals, according to the method described at the article _Test-glass
with a foot_. Obstruct entirely the canal which separates one of these
feet; choke to a certain extent the passage between the two remaining
bulbs; and close the canal between the other foot and the bulbs, after
introducing the quantity of sand which you have found to be necessary.
See pl. 3, fig. 13.

       *       *       *       *       *

HYDRAULIC RAM.--This instrument is represented by pl. 4, fig. 15.
Employ a tube about six feet long, with thick sides and of large
diameter. Seal it at one extremity, _k_, and border it at the other;
solder at _p_ an additional piece, choked so as to receive a valve.
Pierce the tube at _l_; draw it out, and fix a funnel there; then
twist the tube into a spiral. Form, on the other hand, a fountain of
compression, _o_, and a funnel, _m_; and fix both of these pieces by
means of sealing-wax, as soon as the two valves _p_ and _l_ have been
put into their places.

       *       *       *       *       *

HYDROMETERS.--_Hydrometers_ are instruments which, on being plunged
into liquids, indicate immediately their density or specific gravity.
_Areometers_ differ from hydrometers sometimes in graduation, sometimes
merely in name. The following are examples of hydrometers, of which a
great many varieties are in use.

       *       *       *       *       *

BAUMÉ’S HYDROMETER.--Make a cylinder between two points, and solder
it to the extremity of a tube with thin sides, and which must be very
regular on the outside. Close the open part which is to form the stalk
of the hydrometer with a little wax. See pl. 1, fig. 9 and 15. When the
soldering, which must be well done, is complete, and the stalk well
centered, choke the reservoir at a little distance from the base of the
point, by drawing it out in such a manner as considerably to diminish
the canal in this part. Remove then the ball of wax which closed the
tube, draw off the point of the cylinder, and make the part which was
pulled away from the cylinder by the choking, into a bulb, by blowing
with precaution into the tube. If the reservoir is required to be
spherical instead of cylindrical, it must be softened and expanded by
blowing. When it is intended to ballast the instrument with mercury,
the canal must be completely stopped at the point where it is choked.
In this case, the part drawn away from the cylinder is expanded into a
bulb by blowing through the extreme point, which is to be cut off after
the instrument is completed.

In the first case, you ballast the instrument with lead shot, which you
fix in the lower bulb by means of a little wax, which closes the canal
at the choked part. In the second case, after having proved the ballast
by putting it first into the large reservoir, it is removed into the
little bulb, and the latter is immediately sealed.

One of the essential conditions of a good hydrometer is that the stalk
should keep a perfectly vertical position when the instrument is
plunged in water. If, therefore, on proving the ballast, you perceive
the stalk to rest obliquely, you must take care, on retiring it from
the water, to wipe it dry, and to present the choked part between the
cylinder and the little bulb to the flame; when it is softened, it is
easy, by giving it a slight bend in the direction where the stalk of
the hydrometer passes from the vertical, to rectify the defect.

Finally, when the instrument is ballasted, you must seal the stalk,
after having fixed in its interior the strip of paper which bears the
graduated division.

This method of operation serves equally for all the areometers known
under the names of _areometer of Baumé_, _pèse-sels_, _pèse-liqueurs_,
_pèse-acides_, and _hydrometers_, which differ only in the scheme of
their graduation. As to the _size_ and the _length_ of the stalks,
they depend upon the _dimensions_ you desire to give to the degrees of
the scale, and upon the _use_ to which the instruments are destined.
For the areometer of Baumé, and for the _pèse-sels_, the stalks are
generally thicker and shorter than for hydrometers. Pl. 4, fig. 19, 20,
and 21, represent different hydrometers.

       *       *       *       *       *

NICHOLSON’S HYDROMETER.--Solder a bulb to the extremity of a capillary
tube; open it so as to form a very wide funnel, or rather capsule;
border the edges, and melt the point of junction with the tube so as to
close the opening of the latter. Solder the other extremity of the tube
to a cylindrical reservoir. Soften the point at the lower extremity of
the cylinder, and obstruct the canal so as to convert the point into a
glass rod; bend this rod into a hook. Now blow a bulb at the end of a
point, as if to make a mercury funnel; but, after having softened the
hemisphere of the bulb opposite to the point, and placed the latter in
the mouth, instead of blowing into the bulb so as to make a funnel,
strongly suck air from the bulb: by this means the softened part of the
glass is drawn inwards, and you obtain a capsule with double sides,
as exhibited by pl. 2, fig. 17. This capsule must have a small handle
fastened across it, by which it may be hung to the hook formed at the
bottom of the cylinder described above.

This hydrometer being always brought to the same level, the point to
which it must be sunk in the liquid experimented with, is marked on
the stalk by applying a little spot of black enamel. The instrument is
represented by pl. 4, fig. 23. A variation in form is shewn by pl. 4,
fig. 22.

       *       *       *       *       *

HYDROMETER WITH TWO BRANCHES.--To measure the relative density of two
liquids which have no action on each other, you employ a simple tube,
bent in the middle and widened at its two extremities. See pl. 2, fig.
11.

       *       *       *       *       *

HYDROMETER WITH THREE BRANCHES.--This consists of a tube bent in such
a manner that the two branches become parallel. To this tube another
is soldered at the point of curvature, and is bent in the direction
exhibited by pl. 2, fig. 12. When the two branches are put into
different liquids, and the operator sucks air from the third branch,
the two liquids rise in their respective tubes to heights which are in
the inverse ratio of their specific gravities.

       *       *       *       *       *

HYDROMETER WITH FOUR BRANCHES.--This is merely a tube bent three times,
and widened at its extremities. Pl. 2, fig. 13.

To graduate hydrometers with two, three, and four branches, you have to
divide their tubes into a certain number of equal parts.

       *       *       *       *       *

MANOMETERS.--Make choice of a tube nearly capillary, very regular in
the bore, and with sides more or less thick, according to the degree
of pressure which it is to support. Seal this tube at one end, blow a
bulb with thick sides near the middle, and curl it in S, just as is
represented by pl. 2, fig. 9. For manometers which serve to measure
the elasticity of the air under the receiver of the air-pump, what is
generally employed is a tube closed at one end and bent into a U. Pl.
2, fig. 10. You should take care to contract these at some distance
from the sealed part, in order to avoid the breaking of the instrument
on the sudden admission of air. Manometers are graduated, as will be
explained in the sequel.

       *       *       *       *       *

MARIOTTE’S TUBE.--This is represented by pl. 2, fig. 7. It consists of
a tube thirty-nine inches long, closed at one end, bordered and widened
at the other, and bent into a U at the distance of eight inches from
its sealed end. The graduation of this instrument will be described
hereafter.

       *       *       *       *       *

PHOSPHORIC FIRE-BOTTLE.--This is a short piece of tube closed at one
end, and widened and bordered at the other, in such a manner as to
receive a cork. Pl. 3, fig. 34. It is in this little vessel that the
phosphorus is enclosed. Glasses of this form can be employed in a great
variety of chemical experiments.

       *       *       *       *       *

PULSOMETER.--This instrument consists of a tube, of which each
extremity is terminated by a bulb; it is partly filled with nitric
ether, and sealed at the moment when the ebullition of the ether has
chased the atmospheric air wholly from the interior of the vessel. Pl.
2, fig. 16.

       *       *       *       *       *

PUMP.--Solder a cylinder, B (pl. 4, fig. 12), to the extremity of a
small tube, C, and form their point of coincidence into a funnel, to
which you will adapt a valve. Pierce the wide tube or body of the pump
at D, and solder there a piece of tube bent into an elbow and widened
at the other end into a funnel, which is to be furnished with a second
valve, as is represented in the figure. Prepare then the fountain of
compression E, and, by means of a cork and a little sealing-wax, fix it
upon the branch D. To prepare the piston, A, blow a bulb at the end of
a tube, flatten the end of the bulb, and choke it across the middle,
in order to form a place round which tow can be twisted, to make it
fit the tube air-tight. Finish the piston by twisting the other end of
the tube into a ring, as at A. The valves are formed of small cones of
cork, or wood, having in the centre an iron wire of sufficient size and
weight to enable them to play well.

       *       *       *       *       *

RETORT FOR CHEMICAL EXPERIMENTS.--Plate 3, fig. 9, represents a
combination of a large and a small tube, forming a retort, which can
be employed with much advantage in many chemical experiments. When a
gas is to be distilled by means of such a vessel, the ingredients are
put into the wide tube, which is previously closed at one end, and then
the other end of the tube is either drawn out or soldered to a narrow
tube. Pl. 3, fig. 8 and 29, represent such vessels under different
forms. Very often a sort of retort can be formed by joining a wide tube
to a long bent narrow tube, by means of a cork.

       *       *       *       *       *

TUBULATED RETORT.--This is represented by pl. 3, fig. 6. Prepare a
retort, such as is described in the preceding article, but one which
is bent near the closed end; pierce it at A (fig. 6), and solder
there a little piece of tube previously drawn out and sealed, such
as is represented by pl. 1, fig. 11. When the soldering is finished,
soften the end of the little tube, pierce it, and fashion it into a
bottle neck, so that it can be closed by a cork. Finish the instrument
by forming the open end according to the purpose to which it may be
destined. In the figure, the end is represented as drawn out for the
convenience of blowing into the retort to pierce the tubulure.

       *       *       *       *       *

RUMFORD’S THERMOSCOPE.--This instrument is represented by pl. 3, fig.
35. It is necessary to take a tube almost capillary, to solder a bulb
at each extremity, to pierce it laterally at _b_, and to solder there a
piece of tube previously drawn out, but of which you open the point for
the purpose of finishing the sealing of the bulb A. After doing this,
you bend the two branches, as shewn in the figure. When the liquid has
been introduced into the instrument, you must seal the little piece of
tube which serves as a reservoir.

This instrument can be made in another manner. Take two pieces of tube,
one of them twice as long as the other; solder a bulb at one end of
each of these tubes, and at about the third part of the length of the
long tube, parting from the bulb, bend it at a right angle; pierce the
little tube at a corresponding distance, and solder to the hole the end
of the long tube. The soldering being finished, and the whole system
having the form indicated by pl. 3, fig. 35, introduce, by the open end
of the short tube, a small quantity of coloured acid, and then seal the
end of the short tube, which serves as a reservoir.

The interior diameter of the tubes which are generally employed as
thermoscopes, is one-eighth or one-twelfth of an inch. The mode of
graduation is described in a subsequent chapter.

       *       *       *       *       *

SYPHONS.--The _simple syphon_ is a glass tube bent, at a little
distance from the middle, into a form which is intermediate between
those of ⋂ and ⋀, the legs being stretched apart like those of the
latter, but the bend being rounded like that of the former. The tube
is bent _near_ the middle, and _not exactly at_ the middle, in order
that the legs may be of unequal lengths; an arrangement which is
indispensable. Syphons are made of different lengths and diameters, for
various purposes. They can be made of tubes so capillary that it is
sufficient to put them into water to make them act: the liquid rises in
them by capillary attraction, and does not require to be sucked through
the tube, as it does when large syphons are employed.

       *       *       *       *       *

WIRTEMBERG SYPHON.--This syphon is the same as the simple syphon,
excepting that the two branches are of equal length, and are bent in U
at both extremities. Pl. 3, fig. 22.

       *       *       *       *       *

SYPHON WITH THREE BRANCHES.--This instrument is represented by pl. 2,
fig. 19. Close a tube at one end and draw it out at the other; pierce
it at some inches from the contracted extremity, and solder to the
hole a little tube of which the other end has been closed with wax.
Give the tube the bend necessary to constitute a syphon, and open the
two branches. The soldering of the two tubes is facilitated by giving
to the extremity of the little tube a bend which adapts it to be
applied parallel to the large tube. When the syphon is desired to be
well finished, the mouth-piece of the little tube must be bordered and
widened, and a bulb must be blown near the mouth-piece.

       *       *       *       *       *

SYPHON WITH JET OF WATER.--This instrument is represented by pl. 3,
fig. 1. Take a tube of a large diameter, close it at one end, and draw
it out at the other. Cut the contracted part in such a manner as to
be able to introduce, through the orifice, the extremity, also drawn
out, of another tube, which should be almost capillary. Solder these
together in such a manner that the point of the small tube shall remain
fixed about an inch within the interior of the reservoir. Pierce again
the latter, at B, and solder there another branch of the same diameter
as the former; but fix it in such a manner that its side shall be
contiguous to the side of the reservoir. Finally, give to the branches
the bend represented by the figure.

       *       *       *       *       *

SPOONS.--Solder a bulb to the extremity of a capillary tube; open the
bulb as for a funnel, but make the opening laterally. Cut with scissars
the edges of the part blown open, and in such a manner as to form a
spoon or a ladle, according as the bulb had the form of a sphere or an
olive. This instrument is useful for taking small quantities of acids.
Pl. 3, fig. 11.

       *       *       *       *       *

SPIRIT LEVEL.--The spirit level is represented by pl. 2, fig. 28.
Choose a piece of tube very straight, and with sides precisely of
the same thickness in all parts. Seal it at one end, and draw it out
abruptly at the other. Fill it almost entirely with alcohol, and seal
the point by the jet of a candle.

       *       *       *       *       *

TEST GLASS WITH A FOOT.--Take a tube drawn out at one end; choke it at
an inch from the base, in such a manner as to obstruct the canal almost
entirely. Pl. 1, fig. 12. Cut off the point, close the opening, and
soften the whole end completely; then blow it into a bulb and burst
it into a funnel. Now present the contracted part to the fire, so as
totally to close the passage. Border and soften the funnel, and by
pressing it against a flat plate of metal give it the form of a foot,
or pedestal. Cut the tube at the length which you desire the test-glass
to have, and border the edges of the opening. This is a very useful
little chemical instrument. It is represented by pl. 3, fig. 10.

       *       *       *       *       *

THERMOMETERS.--Thermometers are instruments employed for appreciating
changes of temperature, either in the atmosphere or in substances which
we have occasion to examine. The following are the principal varieties
now employed.

       *       *       *       *       *

ORDINARY THERMOMETER.--If you desire to make standard thermometers,
you must have capillary tubes of perfect accuracy in the bore. You are
assured of regularity in the diameter of a tube when a drop of mercury,
made to pass along the canal by means of a gentle inclination, or by
air blown from an Indian-rubber bottle, gives everywhere a metallic
column of the same length.

For ordinary thermometers this precaution is superfluous. In all cases
you employ a tube more or less capillary, at one of the extremities
of which you blow or solder a spherical or cylindrical reservoir.
See pl. 4, fig. 1 and 2. You fill the instrument with well-purified
mercury, or alcohol, which you boil in the tube, in order to chase the
air from it. As it is necessary to heat the instrument throughout its
whole length, you must place it on a railing of iron wire, inclined
in the manner represented by pl. 4, fig. 14, and covered with burning
charcoal, or red-hot wood ashes. It is better, however, to employ a
kind of muff, formed of two concentric wire grates, between which you
put burning charcoal, and reserve the centre for the instrument. The
tube is thus kept in a vertical position, which allows the bubbles
of air to escape with more facility. An iron wire is made use of to
fasten the tube precisely in the centre of the column of fire. The
operation is considerably promoted by soldering a little funnel to the
upper extremity of the thermometer tube; and, in order to avoid the
interruption of the column of liquid by bubbles of air, it is better
to give to the superior part of the reservoir the form of a cone (pl.
4, fig. 3), rather than to preserve the completely spherical form
indicated by pl. 4, fig. 2.

When the ebullition has expelled all the air which was contained in the
mercury, or alcohol, you immediately plunge the open extremity of the
instrument into a vessel filled with one or the other of these liquids;
or, instead of this, you pour the liquid into the funnel, in order that
the instrument may be quite filled at the common temperature. You then
cut off the funnel, if one has been used, and, by properly elevating
the temperature of the reservoir, you expel so much of the liquid
that the summit of the column rests at the point which you desire to
make choice of for the mean temperature: this operation is termed
_regulating the course of the thermometer_.

There are two methods of closing thermometers: you may either produce
a vacuum above the column of mercury, or you may allow air to remain
there. In the first case, after having drawn out the end of the tube,
you heat the liquid until a single drop passes out of the opening; you
then instantly bring the point into the jet, and seal it.

In the second case, you seal the instrument at the ordinary
temperature, and having previously raised to a reddish-white heat the
button of glass which is formed by the sealing, you suddenly elevate
the temperature of the mercury. The liquid, on rising, compresses
the enclosed air, which dilates the red-hot button at the summit of
the tube, and produces a species of reservoir. This reservoir is
indispensably necessary when you leave air above the column of liquid,
in order to provide against the bursting of the instrument on those
occasions when the temperature of the mercury comes to be considerably
elevated. See pl. 4, fig. 13.

       *       *       *       *       *

DIAL THERMOMETER.--Terminate a piece of tube, of six-tenths of an inch
in diameter, with two points, and solder to one of these points a tube
one-eighth of an inch in diameter and six inches long; close the end of
this small tube, and, heating a zone of the reservoir, near the base of
the other point, blow a bulb there. Cut off the point by which you have
blown, at a little distance from the bulb; open and border the end of
the narrow tube, and bend it into a U. See pl. 4, fig. 16.

Fill the bulb and the reservoir with alcohol, and add a drop of mercury
which fills a certain space in the narrow tube. This mercury bears
on its surface a little iron weight, to which a thread is fastened;
the other end of this thread passes over a pulley, whose axis turns a
needle. The expansion or contraction of the alcohol causes the mercury
to rise and fall, and consequently produces a movement of the needle or
index of the dial. This thermometer is graduated like the others, by
being brought into comparison with a standard thermometer.

       *       *       *       *       *

CHEMICAL THERMOMETER.--This instrument is merely a common thermometer,
the divisions of which, graduated on paper, are enclosed in a very
thin glass tube, to hinder them from being altered or destroyed when
the instrument is plunged into liquids. Pl. 4, fig. 4, 5, 6, and 7,
represent chemical thermometers of various kinds.

The case of the thermometer can be made in two different ways.
According to the first, you take a tube of a pretty large diameter, and
with very thin sides; you draw out one end and obliterate the point,
which you bend into a ring, in a direction perpendicular to that of
the case; you pass through this ring the stalk of the thermometer,
which is thus placed parallel to the large tube. After having fixed
the graduated scale in the interior of the case, by means of a small
drop of sealing-wax, which has been dropped on the slip of paper, and
which, being supported against the side of the case, needs only to be
warmed to adhere there and fix the scale securely to its envelope, you
close the upper extremity of the case by drawing it out, obliterating
the canal and soldering it to the thermometer tube which has been
introduced into the ring at the lower end of the case. You heat the
connecting piece till it is soft, and then push the thermometer up and
down until the zero marked on its tube corresponds with the zero marked
on the scale within the case. See pl. 4, fig. 6 and 7.

The second method of making the case is as follows:--You take a
tube with thin sides, and sufficiently large to contain the entire
thermometer; you draw out the tube at one end, and choke it at some
distance from the point of the contracted part. This you must do in
such a manner as to form a little bulb, which is to be ballasted
in the manner described at the article _Hydrometers_. After having
introduced into the case a little ball of cotton, you place therein the
thermometer, furnished with its scale, and in such a manner that the
reservoir rests on the cotton. You terminate the upper end of the case
either with a ring or by a contraction which permits the instrument to
be suspended by a cord. See pl. 4, fig. 4 and 5.

       *       *       *       *       *

SPIRAL THERMOMETER.--Take a tube which is not capillary, but which has
thin sides; close one of its ends, and bend it round by pressing it
with a metallic rod; continue to bend it round till it has made several
turns, all in the same plane. See pl. 1, fig. 13. The latter turns
may be managed with the fingers instead of the metallic rod. When the
reservoir so formed is sufficiently large, solder to the end of it a
capillary tube, which you point in a direction perpendicular to that of
the axis of the spiral. The instrument is represented by pl. 4, fig. 8.

       *       *       *       *       *

POCKET THERMOMETER.--The pocket thermometer differs in nothing from the
thermometer just described, except that the capillary tube, instead of
passing away from the spiral in a straight line, is turned round, so as
to form a continuation of the spiral. See pl. 4, fig. 17.

       *       *       *       *       *

MAXIMUM THERMOMETER.--This instrument consists of an ordinary mercurial
thermometer, bent at a right angle near the origin of the reservoir,
and in the horizontal column of which a little steel or iron rod has
been introduced: this rod, by gliding in the tube, where it experiences
very little friction, serves as an index. Since this index does not
permit the instrument to be sealed with the vacuum above the mercury,
you must terminate the sealing by a little reservoir, as we have
described at the article on the second method of closing thermometers.
The instrument is represented by pl. 4, fig. 24.

       *       *       *       *       *

MINIMUM THERMOMETER.--This instrument is constructed pretty nearly in
the same manner as the preceding. The liquid, however, must be alcohol,
and the index a little rod of enamel, which ought not to be quite so
large as the bore of the thermometer tube. You seal the tube by making
a vacuum above the column.

       *       *       *       *       *

BELLANI’S MAXIMUM THERMOMETER.--This thermometer is represented by pl.
4, fig. 9. Take a tube which is very regular, and about one-eighth or
one-twelfth of an inch diameter in the bore; solder a reservoir at each
end, one of them much larger than the other; make a bend near the large
reservoir, and then fill the instrument with alcohol to A. Above that,
place the first index, which consists of a very small piece of tube
closed at one end and cut off square at the other. In the interior of
this tube the two ends of a hair are fixed, by means of a little rod of
iron, which is pushed into the tube. Introduce a quantity of mercury
above this index, make the bend B, add again mercury as far as C, then
another index similar to the first. Finally, fill the rest of the tube
and the half the little reservoir with alcohol, and seal the point.

       *       *       *       *       *

DIFFERENTIAL THERMOMETER.--This instrument is represented by pl. 3,
fig. 14. Take a tube ten or twelve inches long, and one-eighth or
one-twelfth of an inch internal diameter; blow a bulb at one end, and
bend the tube at a right angle towards the fourth part of its length.
Prepare a second tube in the same manner, and solder the bent ends
together, so as to form a single tube with a bulb at each end, having
previously poured into one of the bulbs a small quantity of sulphuric
acid tinged red.

Instead of following the above method, you may take a single tube of
twenty or twenty-four inches in length, and of the above-mentioned
diameter; you solder a bulb at each end, bend the tube twice till it
represents the figure, pour in the acid, and then seal the open points.
The graduation of the differential thermometer, as well as of all the
other thermometers, is described in a subsequent section.

       *       *       *       *       *

TUBE FOR CRYSTALLIZING SPERMACETI.--Take a little capillary tube; curl
one of its ends into a ring, and solder the other to a cylindrical
reservoir, two-thirds of the capacity of which you fill with very pure
spermaceti dissolved in sulphuric ether; you then seal the point of the
reservoir. See pl. 3, fig. 27.

       *       *       *       *       *

TUBE FOR DEMONSTRATING THE NON-CONDUCTABILITY OF HEAT BY LIQUIDS.--This
is represented by pl. 2, fig. 26. It is a tube sealed at one end,
bordered at the other, and bent in such a manner as conveniently to
permit the upper part of a column of liquid to be exposed to heat.

       *       *       *       *       *

TUBE FOR ESTIMATING THE DENSITY OF VAPOURS.--Represented by pl. 2, fig.
14. It is merely a tube sealed at one end, bordered at the other, and
bent as shewn by the figure.

       *       *       *       *       *

TUBES FOR EXPOSING SUBSTANCES TO HEAT AND GASES.--This instrument
consists of a tube bent in the middle into a U. Pl. 3, fig. 3. It is
much employed in chemistry, for containing substances which we wish at
the same time to expose to an elevated temperature and to the action
of certain gases. This tube can also be employed for cooling gases, or
liquids, in distillation; the bent part being, in this case, dipped
into water or a freezing mixture, or enveloped in wet paper or cloth.

       *       *       *       *       *

TUBES FOR THE PRESERVATION OF OBJECTS OF NATURAL HISTORY, OR OF
CHEMICAL PREPARATIONS.--Take a tube of which the width and length
corresponds with the object which is to be enclosed; draw it out at
one end, and, after having obstructed the point, twist it into a ring.
Introduce the object by the open extremity, which you must afterwards
draw out; fill the tube with the liquid necessary to preserve the
object, and then seal the point. See pl. 2, fig. 27.

If you desire to have the power of taking out the object at will--as,
for example, when grain is preserved, or when, in chemistry, the tube
is employed to contain salts and other compounds, of which small
quantities are now and then required for use--you do not seal the end
of the receiver, but border it in such a manner that it can be closed
by a cork.

In some cases a cork is not sufficient to secure the substance from
the action of air: it must then be assisted with a little cement. By
melting together two parts of yellow wax, one part of turpentine, and a
small quantity of Venetian red, a very useful cement for such purposes
is obtained.

It is sometimes necessary to _suspend_ the objects enclosed within the
tube: you then introduce a little glass hook, the tail of which you
solder to the upper extremity of the tube; managing this operation at
the same time that you make the external ring for the support of the
instrument. By turning the hook round cautiously, which is done when
the end of the tube is in a soft state, and by cooling the whole with
care, you may succeed in fixing the hook in the centre of the tube. See
pl. 3, fig. 20.

       *       *       *       *       *

TUBE FOR EMPTYING EGGS.--It is a simple tube, drawn out to a capillary
point at one end, and bent there into a V. See pl. 3, fig. 23.

The application which the author has made of this instrument, and of
the tube represented by pl. 3, fig. 26, has been shewn in a memoir
inserted in the _Annales des Sciences Naturelles, Tom. XV. Novembre_
1828, concerning a new method of preparing and rendering durable
collections of eggs destined for cabinets of Natural History.

       *       *       *       *       *

VIAL OF THE FOUR ELEMENTS.--This instrument is represented by pl. 2,
fig. 27. Take a tube drawn out at one end, obstruct the canal two
inches from the extremity, and twist the contracted part into a ring.
Draw out the other end of the tube, introduce the proper liquids,
remove the point of the tube, and seal it. The liquids generally
employed for filling the vial of the four elements are, 1. Mercury;
2. A very concentrated solution of carbonate of potash; 3. Oil of
turpentine; 4. Alcohol. A portion of air is also allowed to remain in
the tube.

       *       *       *       *       *

WATER HAMMER.--Pl. 2, fig. 18, is a representation of this instrument.
Choose a tube of a good diameter, and with thick sides; seal it at
one end and draw it out at the other. Blow a bulb at the base of the
contracted part; then, having put a quantity of water in the tube, let
it boil therein, to expel the atmospherical air. When you imagine that
all the air has been expelled, and that nothing remains in the tube but
steam and water, seal the open point.

When you have to seal a tube in this manner, you should be careful
to draw out the extremity of the tube somewhat abruptly, and leave
a very small opening, so that it shall be sufficient to expose the
point to the jet of a candle blown by a mouth blowpipe, to have the
sealing completely and suddenly effected. You can afterwards round
this sealed part by turning it in the flame of the lamp, provided,
however, that you have preserved a sufficient thickness of glass at the
sides of the point. If you omit to take this precaution, the pressure
of the atmosphere, acting with great force on the softened glass when
it is unsupported by the partial vacuum within the tube, is capable
of producing such a flattening, or even sinking in of the matter,
as could not subsequently be rectified; except, indeed, by heating
simultaneously the liquid contained in the tube and the glass to be
mended, which is an operation of a very delicate description.

       *       *       *       *       *

WELTER’S SAFETY TUBES.--After having closed a tube at one end and
drawn it out at the other, give it the curvature exhibited by plate 3,
fig. 18. Pierce it then laterally, in the middle of the part _a b_,
and solder there the extremity of a tube, to the other end of which a
funnel has been soldered: it is necessary that the funnel be closed by
a cork. The soldering being terminated, a bulb must be blown and the
tube bent in S, in the manner shewn by the figure. Then open the closed
end, and cut off the contracted point.




THE

ART OF GLASS-BLOWING.

V.--_Graduation of Chemical and Philosophical Instruments._


OF THE SUBSTANCES EMPLOYED IN THE PREPARATION OF THESE INSTRUMENTS.

Before proceeding to the subject of _graduation_, it is necessary
to say a few words respecting the substances which are generally
employed to fill a variety of instruments, particularly barometers and
thermometers.

_Mercury._--It ought to be completely purified from all foreign
substances. You can separate it from the dust it may contain by passing
it through a piece of chamois leather; you tie a very hard knot,
and by pressure oblige the mercury to pass out in a fine rain. This
process is sufficient for the purification of mercury which merely
contains extraneous bodies in suspension; but it is not sufficient
when the mercury to be purified contains tin, lead, or other metals,
in solution. It is then necessary to distil the mercury; upon which
the fixed metals remain behind. The oxide of mercury produced by the
distillation is removed by agitating the distilled metal with sulphuric
acid, and subsequently washing it with a large quantity of water, till
all the acid is removed; it is then dried as completely as possible
with blotting-paper, and afterwards is moderately warmed.

_Alcohol_ ought to be very pure and well rectified. It is necessary to
colour it, because, being colourless of itself, it could not be seen
in capillary tubes. To colour alcohol, you infuse carmine in it, and,
after some time, decant or filter the clear solution. The liquid should
be perfectly transparent, and free from all extraneous substances.
It is not proper to employ alcohol in the construction of standard
thermometers; mercury being much preferable.

_Sulphuric Acid._--It is made use of for the differential thermometer,
and the thermoscope of Rumford. It has the advantage of being lighter
than mercury, and very slightly volatile: these two qualities, joined
to its tendency to absorb the vapour of water, render it very proper to
be employed for various instruments. It must be very concentrated, and
tinged red by carmine.

_Ether._--Sulphuric and nitric ether, with which some small instruments
are filled, are merely employed to shew with what facility these
liquids are brought to their boiling point.

       *       *       *       *       *

OF GRADUATION IN GENERAL.--Graduation, generally speaking, consists
in dividing lines, surfaces, and capacities, into a certain number
of equal or proportional parts. It is not our intention to treat here
of the methods furnished by practical geometry for effecting such
divisions with mathematical accuracy; these methods are known to
every body. We shall confine ourselves to describing the processes of
graduation which are peculiar to the instruments constructed by the
glass-blower.

       *       *       *       *       *

EXAMINATION OF THE BORE OF TUBES.--We have already observed, that, for
standard thermometers and other instruments which require to be made
very accurate, it is necessary to employ tubes which are extremely
regular in the bore. When a drop of mercury, passed successively along
all parts of the tube, forms everywhere a column of the same length,
the examiner is assured of the goodness of the tube.

That a tube may be regular in the bore, it is not necessary that the
bore be cylindrical; it is sufficiently accurate when equal lengths
correspond to equal capacities. A tube with a flat canal, for example,
can be perfectly accurate without at all approaching the cylindrical
form. It is only necessary that a drop of mercury occupy everywhere
the same length. We may observe, by,the way, that, in flat canals, the
flattening should be always in the same plane.

       *       *       *       *       *

DIVISION OF CAPILLARY TUBES INTO PARTS OF EQUAL CAPACITY.--As it is
very difficult to meet with capillary tubes which are exactly regular
in the bore, it happens that the tubes which glass-blowers are obliged
to employ have different capacities in parts of equal length. You
commence the division of these tubes into parts of equal capacity by
a process described by M. Gay-Lussac. You introduce a quantity of
mercury, sufficient to fill rather more than half the tube, and make a
mark at the extremity of the column. You then pass the mercury to the
other end of the tube, and again mark the extremity of the column. If
you so manage that the distance between the two marks is very small,
you may consider the enclosed space as concentric, and a mark made
in the middle of the division will divide the tube into two parts of
evidently equal capacity. You divide one of these parts, by the same
process, into two equal capacities, and each of these into two others;
and in this manner you continue to graduate the tube until you have
pushed the division as far as you judge proper.

But it is still more simple to introduce a drop of mercury into the
tube, so as to form a little cylinder, and then to mark the two
extremities of the cylinder. If it were possible to push the drop of
mercury from one end of the tube to the other, in such a manner as to
make it coincide, at every removal, with the last mark, it would be
very easy to divide the tube accurately; but as it is very difficult,
not to say impossible, to attain this precision of result in moving the
column of mercury, you must endeavour to approach exactness as nigh
as may be. You measure, every time you move the mercury, the length
of the cylinder it produces, and carry this length to the last mark,
presuming the small space which is found between the mark and the
commencement of the column to be fairly represented by the same space
after the column. You thus obtain a series of small and corresponding
capacities.

       *       *       *       *       *

GRADUATION OF GAS JARS, TEST TUBES, &C.--If the tube is regular in the
bore, close one end, either by sealing it at the lamp, or by inserting
a cork, and pour into the interior two or three small and equal
portions of mercury, in order to have an opportunity of observing the
irregularities produced by the sealed part. Take care to mark, with a
writing diamond, the height of the mercury, after the addition of each
portion. When equal portions of mercury are perceived to fill equal
spaces, take with the compass the length of the last portion, and mark
it successively along the side of the tube, where you must previously
trace a line parallel to its axis.

For tubes which are irregular in the bore, and where equal lengths
indicate unequal capacities, it is necessary to continue the graduation
in the same manner that you commenced it--that is to say, to fill the
tubes by adding successively many small and equal portions of mercury,
and marking the height of the metallic column after every addition.
These divisions will of course represent parts of an ounce or of a
cubic inch according to the measure which you make use of. When you
have thus traced on the tube a certain number of equal parts, you can,
by means of the compasses, divide each of them into two other parts of
equal length. The first divisions being very close to one another, the
small portion of tube between every two may be considered without much
risk of error as being sensibly of equal diameter in its whole extent.

When the tube which you desire to graduate is long and has thin sides,
it would be difficult to fill it with mercury without running the risk
of seeing it break under the weight of the metal. In this case, you
must use water instead of mercury.

Bell-glasses of large dimensions are graduated by filling them with
water, placing them in an inverted position on a smooth and horizontal
surface, which is slightly covered with water, and passing under them
a series of equal measures of air. But it is then necessary to operate
constantly at the same temperature and under the same atmospheric
pressure, because air is very elastic and capable of being greatly
expanded.

In all cases, tubes, bell-glasses, &c. ought to be held in a position
perfectly vertical. The most convenient measure is a dropping-tube,
on the stalk of which a mark has been made, or a small piece of tube,
sealed at one end, and ground flat at the other; the latter can be
accurately closed by a plate of glass.

The marks which are traced on tubes being generally very close to one
another, you facilitate the reading of the scale by giving a greater
length to those marks which represent every fifth division, and by
writing the figures merely to every tenth division. See pl. 4, fig. 8.
The number of divisions is somewhat arbitrary; nevertheless, 100, 120,
360, 1000, are divisions which, in practice, offer most advantages.

       *       *       *       *       *

GRADUATION OF HYDROMETERS.--Cut a band of paper on which the graduation
of the instrument can be traced, and let fall upon it a little drop
of sealing-wax; then roll the paper upon a little glass tube, and
introduce it into the stalk of the hydrometer. The instrument is
afterwards to be plunged into distilled water, which is carefully kept
at the temperature of 40° F. above zero. Give the instrument sufficient
ballast to make it sink till the point (_a_, pl. 4, fig. 20,) which
you desire to make to represent the density of water, touches the
surface of the water. Mark this point with much precision; it is the
zero of the instrument. The other degrees are taken by plunging the
hydrometer into distilled water to which you have added 1, 2, 3, 4, 5,
&c. _tenths_, or 1, 2, 3, 4, 5, &c. _hundredths_, of the substance for
which you wish to construct the hydrometer, according as you desire the
scale to indicate tenths or hundredths.

When you have thus marked the degrees on the stalk of the instrument,
transfer them to the paper with the help of the compasses. The scale
being completed, replace it in the tube of the hydrometer, where it
must be fixed; in so doing, take care to make the degrees on the scale
coincide precisely with those marked on the stalk.

You can thus procure hydrometers for alcohol, acids, salts, &c. which
are instruments that indicate the _proportion_ of alcohol, acid, salt,
&c. contained in a given mass of water.

But if it were necessary to plunge the hydrometer in a hundred
different solutions in order to produce the scale, it is easy to
conceive that that would be extremely troublesome, especially for
hydrometers which are employed in commerce, and which do not need to be
so extremely accurate. When the density of the mixtures or solutions
is a mean between those of the substances which enter into them, you
may content yourself with marking the zero and one other fixed point,
(_a_ and _b_, pl. 4, fig. 20.) Then, as the stalk of the hydrometer is
evidently of equal diameter in all its extent, you can divide the space
which separates the two fixed points into a certain number of equal
parts. One of these, being taken for unity, represents a particular
quantity of the substance which you have added to a determined weight
of distilled water. By means of this unity you can carry the scale
up and down the stalk of the instrument. It is thus, that, to obtain
a Baumé’s hydrometer, after having obtained the zero by immersion in
distilled water, you plunge the instrument into a solution containing
a hundred parts of water and fifteen of common salt, to have the 15th
degree, or containing a hundred water and thirty salt, to have the 30th
degree. Upon dividing the interval into fifteen or thirty equal parts,
according as you have employed one or the other solution, you obtain
the value of the degree, which you can carry upwards or downwards as
far as you wish.

Among the substances for which hydrometers are required in commerce,
are some which it is impossible to obtain free from water--such are
alcohol, the acids, &c. In this case it is necessary to employ the
substances in their purest state, and deprived of as much water as
possible.

The employment of hydrometers is very extensive: they are used to
estimate the strength of lyes, of soap solutions, of wines, milk, &c.
There is, in short, no branch of commerce in which these instruments
are not required for the purpose of ascertaining the goodness of the
articles which are bought and sold. The employment of hydrometers
would be still more general, if they could be made to give immediately
the absolute specific gravity of the liquids into which they might be
plunged, the specific gravity of water being considered as unity. It is
possible to graduate a thermometer of this description by proceeding as
follows:--

Make choice of a hydrometer of which the exterior part of the stalk is
very regular. Introduce the band of paper on which the scale is to be
written, and then ballast the instrument. Make a mark where the surface
of the distilled water touches the stalk. Remove the hydrometer from
the water, wipe it perfectly dry, and weigh it very accurately with a
sensible balance. Then pour into it a quantity of mercury equal to its
own weight; plunge it again into the water, and again mark the point
where the stalk touches the surface of the water. Pour the mercury out
of the instrument, transfer the two marks to the scale, and divide
this fixed distance into fifty equal parts. Having by this operation
obtained the value of the degree, you carry it upwards and downwards,
to augment the scale. If you take the first point near the reservoir,
the hydrometer will be proper to indicate the density of liquids which
are heavier than water; if you take it towards the middle of the tube,
the contrary will be the case.

If you destine the hydrometer for liquids much heavier than water--such
as acids, for example--you might, after having determined the first
point, add to the original ballast as much mercury as is equal to the
weight of the whole instrument; then the point where the stalk would
touch the surface of the water, and which would be represented by 100,
would be very high, and the second point, which would be found below,
would be represented by 200. On dividing the space into a hundred equal
parts, you would have the value of the degree, which could be carried
up and down for the extension of the scale.

The specific gravities being in the inverse ratio of the volumes
plunged into the liquid, the numbers of the scale which mark the
specific gravities diminish from below; so that, on marking the lowest
point 100, you have, on proceeding upwards, the successive degrees
0·99, 0·98, 0·97, 0·96, &c.

The hydrometers with two, three, and four branches, are graduated by
having their tubes divided into a hundred or a thousand equal parts.
The divisions on each branch must correspond with those on the other
branches.

       *       *       *       *       *

GRADUATION OF BAROMETERS.--The graduation of this instrument consists
in dividing a piece of metal, wood, or ivory, into inches and parts of
inches. The divided rod is then employed to measure the height of the
mercury in the tube. As the rule is moveable, the operation presents no
sort of difficulty: all that is necessary is to make the zero of the
scale coincide with the inferior level of the mercury; the point which
corresponds with the superior level of the mercury, seen in the tube,
indicates the height of the barometric column. It is in this manner
that the cistern barometer is graduated.

But if the barometer is one of those in which the surface of the
mercury is variable, such as the barometer of Gay-Lussac, it is
necessary to have recourse to a different process of graduation. If
the two branches of the instrument are very regular, and of equal
diameter, you first measure with precision the height of the column of
mercury, then divide it in the middle, and fix the scale, which must be
graduated in such a manner that the mark of fifteen inches corresponds
exactly with the middle point. This mode of graduation serves to
indicate merely the apparent height of the barometric column. If you
desire that the scale should immediately indicate the real height, you
must fix the zero at the middle of the column, and then double the
figure which marks each degree.

When you do not wish to write the real height, you make two divisions,
of which one proceeds upwards, the other downwards. You do not, in this
case, double the value of each division, but in observations made with
such a barometer scale you add the degree marked by the two surfaces,
in order to find the real height.

It is in an analogous manner that you graduate the gauges or short
barometers which are employed to measure the density of air under
the recipient of the air-pump. You take the height of the mercury in
the gauge, and fix at the middle of the column the zero of a double
scale, of which one division proceeds upwards, the other downwards;
or, instead of this, if you choose to have only one scale, and that an
ascending scale, you double the value of every degree.

The zero of the barometric scale can be fixed below the inferior
surface of the mercury; but then, to have the real height, it is
necessary to measure precisely the height of the mercury in the two
branches of the instrument, and to deduct the smaller from the larger.

_Dial (or Wheel) Barometer._--The disposition which should be given
to this instrument is precisely the same as that of the _Dial
Thermometer_, described in a preceding section. You make a small iron
weight float on the inferior surface of the mercury, and fix to this
weight a silk thread, which is stretched by a counterpoise, and rolls
over a very moveable pulley. The axis of this pulley carries a needle,
which turns backwards or forwards according as the column of mercury
augments or diminishes. You arrange the whole in such a manner that the
extreme variations of this column cannot make the needle describe more
than one circumference; with this view you give the pulley a diameter
of nearly an inch.

The dial barometer being rather an object of luxury than an instrument
of precision, you graduate it by inscribing the following words, at
full length, on the scale. In pl. 4, fig. 16, for example, you write,

  At the point _a_  Tempest.
       ...     _b_  Much rain.
       ...     _c_  Rain or Wind.
       ...     _d_  Temperate.
       ...     _e_  Fine Weather.
       ...     _f_  Fixed Fair.
       ...     _g_  Very Dry.

You write nothing at the inferior division.

       *       *       *       *       *

GRADUATION OF THE MANOMETER.--The graduation of this instrument
consists in dividing the tube where the air is to be compressed, into a
given number of parts of equal capacity; but as, in general, such tubes
are employed as are nearly capillary and very regular, the operation
is reduced to a linear division, where every degree occupies an equal
space.

       *       *       *       *       *

GRADUATION OF THERMOMETERS. _Construction of Standard
Thermometers._--Having constructed your instrument with a very regular
tube, or one which has been divided into parts of equal capacity, and
having filled it with the proper liquid, according to the instructions
given in a preceding section, the graduation is to be effected as
follows. Procure very pure ice, break it into small pieces, and fill
a vessel with it. When the ice begins to melt, plunge the thermometer
into the middle of it, in such a manner that, without touching the
sides of the vessel, the whole thermometer, or at least that part
of it which contains the liquid, may be covered with ice. Allow the
instrument to remain in this state until, in spite of the gradual
melting of the ice, the surface of the column of liquid remains at
a fixed point, and neither falls nor rises. Mark this point very
carefully on the stalk of the thermometer, either with a thread or a
little drop of sealing-wax, or with the trace of a diamond or a flint.
This is the _freezing point_, the _zero_ of the centigrade scale, the
thirty-second degree of Fahrenheit’s scale.

As for the second fixed point, it is marked during an experiment with
boiling water, performed as follows:--You employ a vessel of tin plate
sufficiently high to enclose the whole thermometer; you pour into this
vessel distilled water, till it is about an inch deep, and then you
heat it. The vessel is surmounted by a cover pierced with two holes,
one of which is intended to receive the stalk of the thermometer, the
other to allow the steam to escape. When, on continuing the ebullition,
you observe that the mercury ceases to rise in the tube, you mark
the point at which it has stopped, just as you marked the first
point. The last mark indicates the _boiling point_; the one hundredth
degree of the centigrade scale, the two hundred and twelfth degree
of Fahrenheit’s scale. You transfer to paper the distance which is
found between the first point and the second point determined, and you
divide this distance into one hundred equal parts, or degrees, for
the centigrade thermometer, into eighty parts for the thermometer of
Réaumur, and into one hundred and eighty for that of Fahrenheit. If
the tube of the instrument is very regular in the bore, the degrees
should be equal in length; if, on the contrary, you have been obliged
to divide it into parts of equal capacity, you find how many of these
parts or little spaces it is necessary to take to constitute one of the
above degrees. You find this by dividing their whole number by 100, or
80, or 180, according to the degrees of the scale which you intend to
make use of. Thus, if you find between the two points fixed by melting
ice and boiling water, three hundred divisions of equal capacity, it is
necessary to include _three_ of these divisions in every _degree_ of
the centigrade scale.

The vessel employed to take the boiling point must be of metal, and its
surface should be perfectly clean and well polished, and have no rough
points. If sand, or other matters, were permitted to repose on the
vessel, and to form asperities, the water would enter into ebullition
at an inferior temperature.

This operation should, moreover, be performed under an atmospherical
pressure, which is indicated by the barometer when the mercury stands
at twenty-nine inches and a half. But as this pressure is different
according to the elevation of the place of operation, and, indeed,
suffers continual variations even in the same place, it follows that
the temperature of boiling water is subject to continual changes,
and that, in the graduation of the thermometer, it is indispensably
necessary to take notice of the height of the barometer at the very
moment that the point denoting the degree of boiling-water is fixed
upon. You succeed in making the necessary corrections by the help of
the following table, which is founded on the experiments of Sir G.
Shuckburg and of the Committee of the Royal Society.

[See the Table on the opposite page.]

_Common Thermometers._--Having, by the method which we have just
described, obtained a _Standard Thermometer_, you may procure with
facility as many ordinary thermometers as you desire. It is proper
to employ the most regular tubes which you can obtain, and when the
instruments are ready to be graduated, you must bring them into
comparison with your standard thermometer. You place them together into
a liquid of which you gradually raise the temperature, and you mark
several points on the scale of the new thermometer, the intervals
between which are subsequently divided into as many degrees as are
marked on the scale of the standard thermometer. Thus, for example,
you mark the 10° and 15°, and afterwards divide the interval into five
equal parts. This gives you the length of a degree on the stalk of the
new instrument. The more you multiply these fixed points, the more you
insure the precision of the thermometer. When you have taken a certain
number of points, you measure the remainder with the compasses.

       *       *       *       *       *

  +-----------------------------------+------------------------+
  |Height of the Barometer in Inches. |                        |
  +-----------------+-----------------+     Correction in      |
  |When the boiling |When the boiling |     1000ths of the     |
  | point is found  | point is found  |    interval between    |
  | by immersing    | by immersing    |     the freezing       |
  | the Instrument  | the Instrument  |   and boiling points   |
  | in _Steam_.     | in _Water_.     |        of Water.       |
  +-----------------+-----------------+------------------------+
  |      ...        |      30.60      | 10 }                   |
  |      ...        |      30.50      |  9 }                   |
  |     30.71       |      30.41      |  8 }                   |
  |     30.50       |      30.29      |  7 }                   |
  |     30.48       |      30.18      |  6 }                   |
  |     30.37       |      30.07      |  5 } Lower.            |
  |     30.25       |      30.95      |  4 }                   |
  |     30.14       |      30.84      |  3 }                   |
  |     30.03       |      30.73      |  2 }                   |
  |     29.91       |      30.61      |  1 }                   |
  |     29.80       |      30.50      |  0 }                   |
  |                 |                 |                        |
  |     29.69       |      29.39      |  1 }                   |
  |     29.58       |      29.28      |  2 }                   |
  |     29.47       |      29.17      |  3 }                   |
  |     29.36       |      29.06      |  4 }                   |
  |     29.25       |      28.95      |  5 } Higher.           |
  |     29.14       |      28.84      |  6 }                   |
  |     29.03       |      28.73      |  7 }                   |
  |     28.92       |      28.62      |  8 }                   |
  |     28.81       |      28.51      |  9 }                   |
  |     28.70       |                 | 10 }                   |
  |                 |                 |The boiling point to be |
  |                 |                 |marked so much higher or|
  |                 |                 |lower than the stand of |
  |                 |                 |the mercury during the  |
  |                 |                 |experiment.             |
  +-----------------+-----------------+------------------------+

The zero, 0°, of the thermometer of Fahrenheit, is taken by means of a
mixture of snow and common salt, and its maximum point is, like that of
the preceding thermometer, taken by means of boiling water; but this
interval is divided into 212 degrees; so that the scale marks 32° where
the centigrade and Réaumur’s scales mark 0°.

The thermometer of Delisle has but one fixed point, which is the heat
of boiling water; this is the zero of the instrument. The inferior
degrees are 0,0001 (one ten-thousandth part) of the capacity of
the bulb and stalk of the thermometer. It marks 150° at 0° of the
centigrade, or 32° of Fahrenheit’s thermometer.

The dial, the maximum and the minimum thermometers, are graduated
according to the same principles as the common thermometers.

You can, with a mercurial thermometer, make the centigrade scale rise
to 300 or 400 degrees above zero; but with an alcohol thermometer,
you must never go beyond the heat of boiling water. On the contrary,
the inferior degrees of the alcohol thermometer can be carried to the
very lowest point, while those of the mercurial thermometer should
be stopped at thirty or thirty-five degrees below the zero of the
centigrade scale, as the mercury then approaches very near the point
of its congelation. In all cases, the degrees of thermometer scales
are indicated by the sign - when they are below zero, and by the sign
+ when they are above it; the -is always marked, but the + generally
omitted. See pl. 4, fig. 6.

We may observe here that it is proper from time to time to plunge the
standard thermometer into melting ice, for the purpose of verifying
its exactness. It has been found that thermometers constructed with a
vacuum above the column of mercury gradually become inaccurate, the
0° ascending, until it corresponds with + 1° or + 2°. This singular
effect is attributable to the constant pressure of the atmosphere,
which, being supported merely by the resistance of the very thin sides
of the thermometer, finally presses them together, and diminishes
the capacity of the reservoir. It is partly for the sake of avoiding
this inconvenience that we consider it good not to make an entire
vacuum above the mercury, but to leave a portion of air in the tube,
and at the same time to form a little reservoir at the summit of the
instrument.

_Differential Thermometer._--To graduate this instrument, you first
maintain the two bulbs at an equal temperature, by which you determine
the first fixed point, which is zero. Then, enveloping one of the
two bulbs with melting snow, and elevating the other by means of a
vessel with warm water, to a known temperature--to 20° Centigrade,
for example--you fix a certain space, which you afterwards divide
into 20 equal parts or degrees. The scale is continued by carrying
successively to each side the known value of a degree.

       *       *       *       *       *

GRADUATION OF RUMFORD’S THERMOSCOPE.--This instrument is graduated by
dividing the tube which separates the two bulbs into equal parts, the
number of which is arbitrary, though, in general, the thermoscope tube
is divided into nine or eleven parts. There is always an odd number of
degrees, and you manage so that the odd degree is found in the middle
of the tube. It carries the mark of zero at each end, and the figures
1, 2, 3, &c. proceed from each end of this middle degree, and form two
corresponding scales.

       *       *       *       *       *

GRADUATION OF MARIOTTE’S TUBE.--You divide the little branch which is
sealed at the end into a certain number of parts of equal capacity,
and the large branch into inches and parts of inches. It is necessary
to take care that the zero of the two ascending scales correspond, and
are situated above the inferior bend formed by the two branches of the
instrument.


THE END.

W. WILSON, PRINTER, 57, SKINNER-STREET, LONDON.





End of Project Gutenberg's The Art of Glass-Blowing, by T. P. Danger

*** 