52 
DR. T. ANDREWS ON THE PROPERTIES OF MATTER IN THE 
different from those for the unmixed gas. It is manifest, therefore, that the law of 
Dalton does not hold under the conditions of these experiments. Like the other 
laws of the gaseous condition of matter, it appears to be strictly true only in the 
(ideal) perfect state. The small differences in the elastic force of aqueous vapour 
when alone and when mixed with air, as given in the original experiments of 
Regnault, are, it is highly probable, due, not to accidental or extraneous causes, but 
to the law of Dalton being only approximately true in the case of such a mixture of 
gas and vapour. 
Fig. 2. 
As no liquid was formed in any of these experiments, it follows that the admixture 
of carbonic acid with a permanent gas, such as nitrogen, has the effect of lowering the 
critical point or critical temperature. It will be remembered that for pure carbonic 
acid the critical temperature is 30‘9°. In order to examine the phenomena with more 
precision, mixtures of carbonic acid and nitrogen were taken containing a smaller 
proportion of nitrogen than the foregoing. 
With a mixture of 6‘2 vol. carbonic acid and 1 vol. nitrogen, and which therefore 
contained 13'9 per cent, of nitrogen, liquid first appeared at the temperature of 3°'5, 
when the pressure was raised to 48’3 atmospheres. As the pressure was increased 
the volume of the liquid augmented, and after each increase of pressure the 
liquid continued for some time slowly to augment. Thus at 82 atmospheres the 
relative volumes of gas and liquid in the above mixture were at first 8 '5 and 5 *S, but 
on leaving the apparatus to itself there was a small increase in the volume of the 
liquid. When the pressure was raised to 102 atmospheres the volume of the gas, at 
first 1 *7, gradually diminished till it became reduced to a minute globule, which also 
at last disappeared, the nitrogen dissolving in the liquid carbonic acid. These are the 
ordinary phenomena of the solution of a gas in a liquid, the gas retaining the form of 
a small globule, as is shown in figure 3a, till it finally disappeared. But on repeating 
the experiment at higher temperatures the phenomena exhibited were very different. 
