PYRONOMICS. 94 
Wollaston’s Cryophorus. 
Faraday’s Condensation Tube. 
In the one side of the tube are placed the materials from which the gas is 
to be generated, as, for instance, cyanide of mercury, &c.; and this part 
being carefully heated over a spirit lamp, the gas will pass over into the 
other side of the tube, and there be compressed more and more, by the 
arrival of successive portions, until condensation ensues by placing the 
extremity in a freezing mixture. 
d. Mixture of Vapor with Air. 
When vapors and gases, or aeriform bodies in general, exercising no 
chemical influence upon one another, become mixed together, they do not, 
like liquids, separate according to, their specific gravities, but each gas 
diffuses itself uniformly throughout the entire space, just as if the others 
were not present. If this were not the case, the watery vapor from streams, 
&c., would, on account of its lightness, speedily become elevated above the 
atmosphere, until, finally, all the water on the earth’s surface would become 
converted into vapor and disappear fromit. The coexistence of two gases 
may be readily exhibited by producing a communication between two glass 
vessels, as in pl. 19, fig. 22, the one containing hydrogen, and the other 
carbonic acid gas. The tension of the mixture, which is diffused uniformly 
through the whole space, is in every case equal to the sum of the tension of 
the individual gases, each one being supposed to fill the entire space exclu- 
sively. 
That vapors resemble gases in this respect may be shown by the apparatus 
represented in fig. 23. Fill a barometer tube with mercury, allowing a 
small portion of the tube to remain free, and immerse it in the mercury of 
the vessel cn, upon which the air contained in the tube will expand, and 
occupy five times, for example, its original space. If some sulphuric ether 
be introduced in the manner previously explained, the mercurial column 
will sink still deeper ; by depressing the tube, however, the space above the 
mercury may be brought to the same amount as before the introduction of 
the ether. Since the air is diffused through the same space as before, and 
this space contains as much vapor of ether as if no air were present, it fol- 
lows that the tension of the mixture must be equal to the sum of the tensions 
of the air previously present, and the saturated vapor of ether for the existing 
temperature. This is completely verified by examining the height of 
the mercury above the level in cz. 
The conversion of liquids into vapors or gases is called vaporization ; it 
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