132 



Drs. Ramsay and Young on 



normal down to a temperature of 13°, the lowest temperature 

 at which observations could be made. With ether the vapour- 

 density was approaching normality at 13°, and from the form 

 of the curve would have doubtless become normal at a lower 

 temperature. In both cases, with increase of temperature 

 and corresponding increase of pressure, the density of the 

 saturated vapour increased towards the critical point with 

 great rapidity, until at the critical point the weight of unit 

 volume of the saturated vapour was equal to that of the 

 liquid. 



At the critical point the heat of vaporization of a stable 

 liquid is theoretically zero ; below that temperature we found 

 it to increase with alcohol and with ether as the temperature 

 fell; with ether the increase was found to be continuous to the 

 lowest observed temperature 13° ; whereas, with alcohol, it 

 becomes practically constant below about 20°. Our calculated 

 numbers correspond well with direct measurements by various 

 observers at the boiling-points under atmospheric pressure. 



Fig. 1. 



Vapour-density (H= 1 at iP and p millini.). 

 Alcohol. 



With acetic acid the results were very different. With 

 rise of temperature above 150° the density of the saturated 

 vapour increased, as with other liquids ; but below that tem- 

 perature (at which the vapour-density was 50*06, the calcu- 

 lated density being 30) the vapour-density, instead of con- 

 tinuing to fall, rose more and more rapidly with fall of 

 temperature, until at 20° the vapour -density was approxi- 

 mately 59, and apparently, from the form of the curve, was 

 continuing to rise more and more rapidly, with fall of tem- 



