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