74 Intelligence and Miscellaneous Articles. 
the atmosphere became equal. Afterwards the liquid disappeared; 
and, in conformity with the theory, it disappeared at very different 
and more considerable pressures for the mixture of hydrogen than 
for that of air. 
Here are M. Cailletet's results reduced, by a graphic con- 
struction, to the same temperature. It will be seen that at 20° it 
requires about 200 atmospheres for hydrogen, and only 100 for 
air. 
Disappearance-pressure for the 
Temperature. mixtures of carbonic acid and 
air. hydrogen. 
15 135 245 
16 130 236 
17 125 227 
18 120 218 
19 114 208 
20 1^8 199 
21 102 190 
22 96 181 
23 90 172 
24 85 163 
25 79 153 
From these experiments, which shall certainly be continued, it 
will be easy to institute a comparison between the densities of air 
and hydrogen at different temperatures and under one and the 
same pressure. 
When the mixture is less rich in carbonic acid, M. Cailletet has 
remarked that the liquefaction of this gas is always retarded, and 
sometimes impossible. In fact, when the total volume is reduced 
by pressure to one tenth or one hundredth, both gases undergo the 
same reduction but not the same increase of pressure : that of the 
air is multiplied by 10 or 100 ; that of the carbonic acid increases 
less quickly, since Mariotte's law is no longer applicable. Hence 
results a retardation of liquefaction ; and when at length the 
carbonic acid has reached its maximum tension and passes into 
the liquid state, its density may have become equal to, and 
sometimes less than, that of the superposed atmosphere. In 
this case it mixes with, floats in the latter, leading one to believe 
that it has lost the property of liquefying under pressure, when it 
has only lost the property of collecting at the bottom of the vessel 
from excess of density. 
Is it not permissible to expect another ending to this experi- 
ment? If the total pressure were augmented indefinitely, the 
carbonic acid would continue to liquefy, and its density would 
change but little, while that of the gaseous atmosphere would be 
indefinitely increased and would become superior to that of the 
liquid, which would perhaps separate ; but then it would collect at 
the top of the tube instead of sinking to the bottom. This second 
