The shelf, with the lamp and the ring having the retort in it, are now to be adjusted by moving them up or down, until the lamp is at a convenient height below the retort, the neck of which rests upon the edge of the cistern, and the end of its neck opens in the funnel under the jar standing upon the shelf. The lamp must now be lighted, and as soon as the substances in the retort act upon each other sufficiently, the gas will begin to be disengaged, and will ascend through the hole in the shelf into the vessel, B, and displace the water with which it had been filled. When all the water is displaced, the receiver is full of the gas which was disengaged from the retort, and may be preserved in it by keeping its mouth always under the water in the cistern.

This gas may be transferred from the vessel, B, into any other vessel, in the following manner: fill the vessel into which the gas is to be transferred, with the fluid in the trough, and place it on the shelf as before directed, over one of the holes. Then take the vessel, B, and keeping its mouth still under the fluid, bring it under the hole on which the vessel is placed, then depressing its bottom, and elevating its mouth, so as to bring it more to a horizontal position, the gas in it will escape and rise up through the hole on which the other vessel has been placed, and will fill it by displacing the fluid. In this manner any gas may be formed, or transferred from one vessel to another."

The cistern for the water may be made of wood, in the manner of a tub, and hooped round, which may or may not be painted inside and out. But it will be much more elegant if made of sheet-iron, tinned, and japanned of a brown or chocolate colour. The ornaments, if any, may be of brass, or

gilt. The best material for the lamp-furnace is brass lackered, and the lamp should be of tin japanned. The apparatus constructed in this manner has an extremely elegant appearance, and is found to answer perfectly well for a variety of chemical operations.

When the gas to be procured is absorbable by water, quicksilver is used instead of water; and, as it is very expensive, a smaller vessel is necessary, which must be made of some material not acted upon by quicksilver, as wood or stone; and it must be sufficiently strong to resist the great weight and pressure of the quicksilver. It is usually cut out of a solid block of wood, or marble, or made very strong of mahogany, and varnished over, to make it perfectly tight.

A small glass vessel, capable of containing an ounce measure, is used for measuring gases; for if this phial be successively filled, and inverted under a large jar, we may thereby throw into that jar any required quantity of an elastic fluid, or as many measures of one elastic fluid, and as many of another, as we please.

G (Fig. 7.), represents a tube for receiving a mixture of gases that are to be exploded by the electric spark. It is a very strong glass tube, closed at one end, and having a scale upon it, cut with a diamond. Near the closed end two wires pass through the glass, and almost touch each other, but not quite; they are cemented in, so as to make the holes air-tight. When this graduated tube is filled with the fluid in the trough, and inverted upon the shelf, certain measures of the gases to be exploded are introduced in the usual way. If thus the interval between the two wires be made a part of the electric circuit, by fastening chains con

nected with a Leyden phial to the rings of the wires, the spark will pass through the interrupted space between the two wires, and explode the gases. These instruments are called exploding

tubes.

In' compound distillations, or when a decomposition of the materials subjected to this process takes place, and gases are formed, some of which are absorbable by water, some by alkalis, and others are not capable of being absorbed at all, it is often required to preserve separate the several new substances procured. The apparatus invented by LAVOISIER for this purpose is the most convenient.

A (Plate 2. fig. 1.), is a glass retort, the beak of which is adjusted to a double tubulated balloon, or receiver, B. To the upper tubulure of this receiver is fitted a glass tube, C, the other extremity of which is conveyed into the liquor contained in the glass vessel, D: with this vessel, D, which has three tubulures, are connected two or three other similar vessels, by means of glass tubes fitted into their tubulures, and to the last tubulure of the range of vessels is adapted a glass tube which is conveyed under a receiver placed upon the shelf of the pneumatic cistern. Water is put into the first of these vessels, caustic potash into the next, or such other substances as are necessary for absorbing the gases, and the joinings are well luted. Sometimes it will happen that a re-absorption of gas takes place; and in this case, that there may be no danger of the water in the pneumatic tub entering rapidly into the vessels through the tube, E, a capillary tube is adapted to the middle tubulure of each vessel, which goes into the liquid con

tained in it. If absorption takes place, either in the retort or vessels, the external air enters through these tubes, to fill the vacuum which is occasioned by the absorption, and no water comes into the vessels.

Large vessels for containing air, and expelling any given quantity, are called gazometers. They are of various constructions; one of the best is the following: AB (fig. 2.), is a cylindrical vessel of tin, japanned, nearly filled with water, and having a tube, C, in the middle, open at top, and branching, to communicate with the cock, D. Within this vessel there is another cylindrical vessel, generally of glass, of smaller size, F, open at bottom, which is inverted and suspended by the lines e e, which go over the pullies ƒ ƒiƒƒ, and have weights g g, attached to them, to balance the vessel, F. While the cock D remains shut, if the vessel F be pressed downwards, the air included within it will remain in the same situation, on the principle of the diving-bell; but if the cock be opened, and the vessel, F, be pressed down, the air included within it will escape through the cock, and if a blow-pipe be attached to this cock, a stream of the gas may be thrown upon lighted charcoal, or any other body. By means of the graduated rod, h, also, the quantity thrown out is exactly ascertained: this rod is so divided as to express the contents of the inner vessel in cubic feet, &c. This instrument also answers for breathing any of the gases, by applying a mouth-piece to the cock. To render it more portable, the weights g g, are sometimes included in the uprights ii, which are hollow, and wide enough to receive them. Sometimes, also, there is another branch from the bottom of the pipe, in

the middle, directed to the side of the outer cylinder, and coming upwards by the side to the top, where there is another cock attached.

For solution, and dissolutions, and for crystallizing salts, vessels of glass or earthenware are used.

The melting, or causing any body to pass from the solid to the liquid state, by the action of fire, is called fusion. The fusion of metallic substances requires vessels sufficiently strong to resist the fire. Those vessels are mostly, if not always, made of earthen-ware, or porcelain, or a mixture of clay and powder of black-lead. They are called crucibles, and are generally of the forms represented Fig. 3. Sometimes these vessels have covers made of earthen-ware; but sometimes the fused metal must be exposed to a current of air: in that case, the crucibles are broad and shallow, as at Fig. 4. these are called cupels, and they are formed of calcined bones, mixed with a small quantity of clay, or of a mixture of clay and black-lead powder. But the cupels must not be placed in a closed furnace, or be surrounded by coals; for, in that case, the required current of air could not have access to the fused metal. They are, therefore, placed under a sort of oven of earthen-ware, which is called a muffle, as represented, Fig.5, which, with the included cupel, is exposed to the heat of a furnace.

The various degrees of heat which are required for the performance of chemical operations render a variety of fire-places, or furnaces, necessary for a chemist. Those furnaces are either open at top, or they are covered with what is called a dome, and have a chimney, or tube, to carry off the heated