22 CHEMISTRY. 
all other elements; at least in many cases all that is necessary to effect this 
combination is the heating of the latter. The apparatus employed for the 
purpose is generally very simple, consisting principally of crucibles, tubes 
of porcelain and glass, capsules, matrasses, flasks, and retorts. 
In most experiments, however, instituted with the gases proper, a large 
quantity of these is required to be kept in convenient vessels. Such vessels 
are known as gasometers. ‘They are socontrived as to permit a convenient 
filling in of the gas, as well as its safe preservation for a considerable length 
of time when not required for use. To this must be added a facility in 
extracting as much or as little as may be needed for experimental purposes. 
Pl. 30, figs. 58 and 59 represent a gasometer of the earlier construction. 
The entire apparatus, consisting of two vessels, is first filled with water, and. 
the cock, Z, closed, so that the water in the flask cannot flow out through 
the tube G. The gas conductor is attached to the tube C, through which 
the gas generated is allowed to enter. The cocks O and o are opened, R 
remaining closed. As the gas enters through the tube CO into the vessel B, 
and rises in single bubbles through the water in this vessel, the water is 
driven out through the open cock, 0, at the bottom. As soon as B is filled 
with gas, the cocks, O, 0, are closed, and the apparatus retained in this state 
until the gas is required for use. To force out the gas when wanted, the 
cock Z must be opened. The air which presses on the flask through 
the tube T, after the openings E ( fig. 59) and F (fig. 58) have been closed, 
drives the water through the bent tube, G, into the gas-vessel, B, here 
displacing the gas, and driving it out through R¢ when the cock R is opened. 
The gas may thus be driven into another vessel, as shown in fig. 59, by 
connecting the extremities of the two brass tubes, ¢’, t’, by caoutchouc.: 
The gasometers of more recent construction are, however, far more 
convenient (pl. 31, figs. 4 and 5). The first figure gives a back, and the 
second a side view of the instrument: A and B are cylindrical vessels made 
of copper or zinc. ‘The upper one is connected with the lower by posts and 
several tubes. The rods e and bb are tubes, provided with cocks, by means 
of which the communication through the tubes between the two vessels may 
be interrupted or restored at pleasure. One tube, bb, reaches nearly to the 
bottom of the vessel A; the other, e, ends on the cover to which it is 
soldered. The glass tube, cc, is so attached to the outside of the lower 
vessel, as that one end communicates with the interior of A at the top, and 
the other end at the bottom. At the bottom of A there is an escape pipe, C, 
capable of being closed by a screw lid. To use the apparatus, the cocks at 
e and b are first opened, and the apertures in (jig. 5) a and ( jig. 4) C are 
closed by their cover. Water is poured into the upper cylinder, which 
enters through the tube bd into the vessel A, while the air ascends through 
the tube e, and escapes in the form of bubbles. When the entire apparatus 
is filled with water, all the cocks are closed, and the screw C opened. As 
the air has no access to the space in A, its pressure on the small surface at a 
or C keeps the water in equilibrium, so that this cannot escape. ‘The tube 
from the gas-generating apparatus is introduced into C, and the gas allowed 
to ascend. Occupying the highest part of A, the gas displaces the water, 
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