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.