Fig. 7. PEPYS' APPARATUS for ascertaining the quantity of carbonic acid discharged from any substance by the addition of an acid; the twisted tube from the bottle performs the office of a still worm, and condenses any liquid that may arise with the gas, causing it to fall down again into

the bottle.

Fig. 8. A MUFFLE; an instrument employed for the purpose of submitting substances to the continued action of a red heat with a considerable exposure to air at the same time.

Fig. 9. A JAR AND GAS RECEIVER,

Fig. 10. APPARATUS for showing that caloric exists in a latent form in gases. a, A retort into which salt and sulphuric acid are placed; two ounces of the former, to half the weight of the latter the gas which this mixture produces is received into a glass balloon, 6, from this a tube, c, descends into a vessel of water, d, of the temperature of the atmosphere. The temperature of the gas in the balloon, b, must be ascertained before the vessel is closed; this is to be done by inserting into it a thermometer, e. In this thermometer the mercury will rise only a few degrees, while the mercury of another thermometer inserted into the water, d, will rise to the boiling point; proving that the latent heat of the gas is given out when condensed by water.

Fig. 11. WOOLFE'S APPARATUS (common form of it), the original inventor of which was Glauber; this was constructed upon the principle, that in gaseous formation some part of it may be absorbable by water, while other parts are not. Now the gas that is not thus taken up by the water would increase in close vessels, so as eventually to asion their bursting. The earlier chemists made a small hole in the upper parts of their retorts to allow the escape of the gas not condensable; but, besides that this implies the loss of a considerable part of the product, it is often necessary to collect separately the gases that are, and are not, condensible by, and soluble in, water, so that it was necessary to have several receivers, or bottles with tubes, to convey away the gases not condensible, and collect them according to the wish of the experimenter. a, Retort. b, First receiver. c, Second receiver. d, Third receiver. e, Bent tube for conveying away unabsorbed gas. The materials introduced into the retort, and the distillation commenced, the vapor collects in the first receiver, and part is condensed while the evolved vapor passes through the tube into the second receiver, the tube terminating beneath the surface of water, which absorbs the produced gas to a certain extent; when this absorption cannot be carried further, the gas passes off into the second bottle, the water of which becomes saturated, and that which is not absorb able escapes through the bent tube, e, and of course if necessary may be collected. It will be perceived that the bottles have middle necks to which long tubes are attached, which communicating with the atmosphere, any occasional vaccuum is immediately supplied from without, and accidents thus guarded against.

Fig. 13. WOOLFE'S APPARATUS, WITH WEL

TER'S TUBE OF SAFETY. This renders the central openings from the bottles unnecessary. A small quantity of water being poured into the

funnel so as to about half fill the ball, bore: when absorption takes place the water rises in the bali till none remains in the tube, and then the air rushes in on the other hand no gas can escape, as it has to overcome the pressure of a high column of water in the perpendicular tub. To this instrument, another form of which is represented, plate I. fig. 3, is appended a mercurial trough, d, and a jar, c, inverted in mercury for collecting the gas that is not absorbable by

water, or condensible.

Fig. 13. A TUBE BLOWN IN THE MIDDLE INTO A BALL FOR DROPPING LIQUIDS. The ball being filled by the suction of the mouth applied to the upper orifice, while the lower one is immersed in the liquid; or by immersing the ball and tube at once into the liquid with the point downwards, then applying the finger to the upper orifice and cautiously removing it, the liquid will pass out in drops.

Fig. 14. The mode in which charcoal or any inflammable body is introduced into oxygen gas for rapid combustion.

EXPLANATION OF PLATE III. Figs. 1, 2, 3. GLASS BOTTLES AND MATRASSES for solutions and experiments upon a small scale. Figs. 4, 5, 6. CRUCIBLES, chiefly used for subjecting substances to a high heat.

Fig. 7. PORTABLE BLAST-FURNACE OF MR. AIKIN.-This is composed of three parts, all made out of the common thin black-lead melting pots sold in London for the use of the goldsmiths. The lower piece, c, is the bottom of one of these pots, and cut off so low as only to have a cavity of about an inch deep, and ground smooth above and below. The outside diameter over the top is five inches and a half. The middle piece, or fire-place, a, is a larger portion of a similar pot, with a cavity of about six inches deep, and measuring seven inches and a half over the top, outside diameter, and perforated with six blast-holes at the bottom. These two pots are all that are absolutely necessary to the furnace for most operations; but when it is wished to heap up fuel above the top of a crucible contained, and especially to protect the eyes from the intolerable glare of the fire when in full height, an upper pot, b, is added, of the same dimensions as the middle one, and with a large opening in the side, cut to allow the exit of the smoke and flame. It has also an iron stem with a wooden handle (an old chisel answers the purpose very well) for removing it occasionally. The bellows, which are double, d, are firmly fixed, by a little contrivance, which will take off and on, to a heavy stool, as represented in the plate, and their handle should be lengthened so as to make them work easier to the hand. To increase their force, on particular occasions, a plate of lead may be firmly tied on the wood of the upper flap. The nozzle is received into a hole in the pot c, which conducts the blast into its cavity. Hence the air passes into the fire-place, a, through six holes of the size of a large gimlet, drilled at equal distances through the bottom of the pot, and all converging in an inward direction so that if prolonged they would meet about the centre of the upper part of the fire. (Fig. 9. shows the distribution of these holes in the bottom.

1

The large central hole is intended to receive a stand for supporting the crucible.) No luting is necessary in using this furnace, so that it may be set up and taken down immediately. Philosophical Magazine, vol. xvii. p. 166. See also Ure's Dictionary, article LABORATORY, and Henry's Elements.

Fig. 8. A FIXED FURNACE, which may be used for a wind-furnace, or for distillation with a sand heat.

ture room.

Fig. 10. MR. AIKIN'S FURNACE, when used for showing the process of cupellation in a lecThe method of using it consists in causing a portion of the blast to be diverted from the fuel and to pass through a crucible in which the cupel is placed. a a, The furnace. b, The perforated stopper for the central blast. cc, A portion of earthen tube through which the air passes, and is heated during this transit, e, A piece of soft brick, perforated to admit the earthen tube, f, which may be kept open for inspecting the process. No luting is required except to join f to e. (Henry). Improvements made by Mr. Aikin in this furnace, may be seen and had of Mr. Knight, in Foster-lane.

Fig. 11. KNIGHT'S PORTABLE FURNACE, composed of strong iron plate, lined with fire-lute, the inside diameter six inches. a, The grate. b, The ash-pit door. d, The door of the fire-place when used as a sand-heat. ee, Two holes, opposite to each other, for transmitting a tube. g, An opening for a retort neck when used for distilling with the naked fire. Dr. Henry, from whom we take this plate and description, says he finds it a great improvement to make the aperture for the chimney at k, as shown in the next figure, instead of directing it through the sand bath, according to the ordinary construction.

Fig. 12. A DIFFERENT VIEW OF THE SAME FURNACE. a, The grate. c, The register of the ash-pit. f, A small door with a contrivance for supporting a muffle.

Figs. 13, and 14, are different views of a furnace of Mr. Knight's invention, and convertible to various purposes. It is nine inches square on its inside, and sixteen inches deep from the top to the grate. The face of the opening at g, fig. 13, rises at an angle which makes the back part five inches higher than the front. If the ashpit, at i, he sunk below the level of the ground, the height of the furnace need not exceed eighteen inches. The ash-pit, a, must be at least eighteen inches deep below the surface of the ground. The grate, b, is formed of separate bars, three-fourths of an inch apart, and of a triangular shape. The chimney, f, is two inches and a half from the top, and four and a half by two and a half wide.

When we wish to apply this furnace to the purpose of occasional distillation, an opening, d fig. 14, is left on one side, which, when not wanted, is filled up by brick. Other pieces of brick may likewise be provided, with arched openings, one of them having a round hole in it, for occasionally transmitting a tube, and a corresponding hole, in fig. 13, must then be made in the opposite side of the furnace, to be closed

when not wanted.

Fig. 15. Is a longitudinal section of a wind

furnace, invented also by Mr. Knight, with an
additional chamber for supplying the waste heat
to useful purposes. a, The internal cavity. b,
The flue, passing into a hot chamber. c, An ap-
pendage for drying, or roasting, &c. d, The flue,
connecting it with the vertical chimney e. ff,
covers, formed of twelve-inch Welsh tiles, with
handles. g, The stoke hole. h, Bearing-bar. k,
Ash-pit, sunk below the level of the ground.

EXPLANATION OF PLATE IV.

OF

Fig. 1. MR. PEPYS' IMPROVEMENT WOOLFE'S APPARATUS.-The balloon, a, is surmounted by a vessel, b, accurately fitted to it, and furnished with a glass valve, allowing gas freely to pass into it, but preventing the water which it contains from falling into the balloon.

Fig. 2. A GASOMETER.-This consists of an outer fixed vessel, a, and an inner moveable one, b, both of japanned iron. The latter slides easily up and down with the other, and cords, passing over pulleys, suspend it, to which the counterpoises, c c, are attached. The gas enters from the vessel in which it has been formed by the communicating pipe, d, and passes along the perpendicular pipe, indicated by dotted lines in the centre, into the cavity of the vessel b, which continues to rise till it is full, and then it is stopped by the cross-bar to which the pulleys are attached.

Fig. 3. GAS RECEIVER.

Fig. 4. A GALVANIC TROUGH, a, a, (See GALVANISM.) The tube, marked b, is the arrangement for decomposing water. a, A trough.

Fig. 5. CUTHBERTSON'S APPARATUS, for showing the composition of water. A glass receiver, a, with an aperture at the bottom, to which a piece of brass is cemented, perforated with two holes, one aperture conveying the oxygen gas, and one the hydrogen.

Fig. 6. A GRADUATED TUBE, for several purposes of experiment.

Fig. 7. APPARATUS FOR DECOMPOSING WATER
over red-hot iron or charcoal.-A Retort, a,
partly filled with water, is to be affixed to a gun-
barrel, b b, open at both ends, c, c, and filled up
with iron wire, coiled up at both ends; the
barrel is to be placed, nearly horizontally, in a
furnace, with a small elevation of that end
nearest the retort. A fire is to be lighted in the
furnace, and when the gun-barrel has become
red-hot a lamp is to be applied under the retort,
a, which will cause the water it contains to pass
through the tube, and over the red-hot iron wire;
it will thus be decomposed, its oxygen uniting
with the iron, and its hydrogen, passing over in
the form of gas, will be received in the pneu-
matic cistern.

Fig. 8. A CHEAP Instrument FOR FREEZING
QUICKSILVER by muriate of lime and snow, a a,
The outer vessel of wood. bb, An inner tin
vessel, standing on feet. cc, A shallow tin pan,
resting on a projection of the inner tin vessel.
Within this is a third, d, made of untinned iron,
and supported by feet two inches high. Into
this vessel the mercury to be frozen is placed,
and the freezing composition is to be placed in
inner one.
the outer one, so as completely to surround the

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