56 DR. T. ANDREWS ON THE PROPERTIES OF MATTER, ETC. 
In an hour and a half diffusion had partially occurred and the volume had increased 
to 161-5. 
At 16 o, 0, and under a pressure of 47'9 atmospheres, the volume of the mixture was 
164’6 ; after liquefaction of the carbonic acid and restoration of the original tempera¬ 
ture and pressure the volume was 161 - 9, or a contraction of 2 '7 volumes. In an 
hour and a half the volume had increased to 164'1. 
Similar experiments at 20°, and under a pressure of 46-4 atmospheres, gave a 
reduction of volume from 175'8 to 173‘5 after separation of the gases. 
It hence appears that when carbonic acid and nitrogen diffuse into one another at 
high pressures an increase of volume takes place; and, on the other hand, when they 
are separated from one another there is a diminution of volume. A similar change of 
volume no doubt occurs at ordinary pressures, but its amount would be so small as to 
render the observation difficult. The result now described is the reverse of what 
commonly happens when liquids diffuse into one another, but it is in accordance with 
what might be expected in the case of the diffusion of two bodies such as carbonic 
acid and nitrogen of unequal compressibility, and which do not combine with one 
another. 
The following are the general conclusions to which this inquiry has led:— 
1. The law of gaseous mixtures, as enunciated by Dalton, is largely deviated from 
in the case of mixtures of nitrogen and carbonic acid at high pressures, and is 
probably only strictly true when applied to mixtures of gases in the so-called perfect 
state. 
2. The critical point of temperature is lowered by admixture with a permanent gas. 
3. When carbonic acid gas and nitrogen diffuse into each other at high pressures 
the volume of the mixture is increased. 
4. In a mixture of liquid carbonic acid and nitrogen at temperatures not greatly 
below the critical point, the liquid surface loses its curvature and is effaced by the 
application of pressure alone, while at lower temperatures the nitrogen is absorbed in 
the ordinary way, and the curvature of the liquid surface is preserved so long as any 
portion of the gas is visible. 
