38 CHEMISTRY. 
cannot be communicated to the outside, owing to the rapid reduction of 
temperature experienced by contact with the metal. 
Davy’s Apparatus for Investigating the Earths (shown in pl. 30, fig. 
61). is intended specially for examining the amount of gas generated from 
a calcareous earth under the influence of an acid. D is a retort containing 
the earth, E a vessel for receiving the acid, provided beneath with a stop- 
cock ; 6 is a connecting tube, to the lower end of which a contracted bladder 
is fastened; B is a retort filled with water, and A a graduated measure. 
After the earth has been introdttced into D, the cock at E opened, and the 
acid let in on the earth, the liberated gas passes through the tube, b, into 
the bladder, c, expands this and thereby displaces an equal amount of water 
from Bb, which passing over to A, indicates by its level at a, the volume of 
gas introduced. 
The Wolff Apparatus (pl. 30, figs. 56 and 57) is intended to be used for 
saturating liquids with soluble gases. Thus, suppose it be desired to 
prepare a saturated solution of chlorine in water, the generating apparatus 
(fig. 56) is applied to the tube, C, and the bottles, A and B, filled one third 
with water. On allowing the gas to enter through C, it gradually displaces 
all the air in the apparatus, and the water in A gradually purifies the gas of 
improper admixtures. The gas then passing over to the bottom of the water 
in B, rises through the water and is in a great measure dissolved, the water 
becoming gradually saturated. The excess of gas, or that which has not 
been dissolved, may be made to pass over into a third flask, and thence to a 
fourth, &c. D and F (in fig. 56) are safety tubes, through which the 
expansive force of the gas may be spent in driving out the water in the 
bottles whenever any obstruction occurs, instead of bursting the vessel. 
Fig. 57 exhibits the apparatus as connected with an apparatus for generating 
the gas. 
Apparatus for making anhydrous hydrocyanic or prussic acid (pl. 30, 
fig. 62). In the cylinder, b, the hydrochloric acid gas is generated, which 
enters through the tube, a, into the porcelain tube, D, in which cyanide of 
mercury has been laid, and where, by the decomposition of these two 
compounds, produced by the heat of the coal fire, G, prussic acid is 
generated. In the hollow, E, of the tubular extension of D, are placed 
pieces of chloride of calcium and chalk, kept cool by the snow with which 
the vessel, ABC, is filled for the purpose of condensing any watery vapor 
which might form, é&c. The hydrocyanic acid vapor enters the tube, F, 
which is surrounded by an artificial freezing mixture, as of salt, snow, and 
dilute sulphuric aid ; by this means the volatile acid is condensed. 
Pharmaceutical Steam Apparatus. Pl. 30, fig. 13, represents a quite 
recent form of steam apparatus very convenient for pharmaceutical purposes. 
The dotted box, A, is the steam boiler. Beneath it is the fire space with 
its door, a, and beneath this,again, the ash-hole to which the door, ), leads. 
From the upper plate, I’, projects the matrass or alembic, C, heated by the 
steam of the vessel, A; G is the extremity of its neck through which the 
produets of distillation pass. Next to this matrass are several openings on 
the plate into which are set the tin boxes, c, c’, c’’, capable of being 
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