130 



EEPOET — 1886. 



least possible below 30'9° tlie gas just becomes liquefied by a pressiu'e of 

 about 74 atmos. 



The temperature 309° and tlie pressure 74 atmos were called by 

 Andrews the critical temperature and pressure for CO.2. In further re- 

 searches Andrews had found that the critical point was not a point special 

 to CO2 and to this body only ; he found a similar behaviour at some point 

 for every liquefied gas or volatile liquid he examined, and in particular for 

 nitrous oxide, hydric chloride, ammonia, ethyl oxide, and bisulphide of 

 carbon. For each of these (and he considered the property to be general) 

 there is a certain temperature below which the body can, by sufficient 

 pressure, be liquefied, and above which no pi'essure, however great, can 

 liquefy it. The smallest pressure which can liquefy it at immediatelij 

 below this critical point is the critical pressure. 



There can be no doubt that in reference to general properties of liquids 

 and gases the critical temperature and pressure are of the greatest im- 

 portance, and that the accurate determination of a number of these will, 

 in conjunction with Andrews' very complete examination of COo and with 

 Amagat's results — carried, as they are, to very high pressures — be among 

 the most valuable data towards a general theory of gases and liquids ; and 

 on the other hand the critical points may be arrived at by a theoretical 

 method, as indicated in a paper by Thorpe and Riicker.' The actual 

 critical temperatures at present known, besides those found by Andrews, 

 have been obtained for the most part by Ramsay in 1880,^ by Pawlew- 

 ski,^ by Olszewski and Wroblewski, by Sajotschewsky, and by Dewar.^ 



In a paper on the liquefaction of oxygen and the critical volumes of 

 liquids,^ Dewar ^ gives a list of twenty-one critical temperatures and pres- 

 sures in atmospheres, of which we will mention a few : — 



where T is the absolute critical temperature=273 + ^. Of the above 

 Dewar determined ammonia, hydric sulphide, cyanogen, marsh-gas, and 

 ethyl hydride. Ansdell determined acetylene. For Ansdell's experi- 

 mental determination of physical constants of acetylene and hydrochloric 

 acid, see ' Proc. Roy. Soc' xxx. 117, and sxxiv. 113. 



Dewar shows in the above paper how by his modification of Cail- 

 letet's apparatus the volume and weight, and hence the density, of the 



» J.C.S. Trans. 1884, p. 135. 



2 Proe. Roil. Soc. vol. xxsi. p. 194. 



» Bcrichte dcr Deutschen Clwmischen. G. xv. p. 2460, 1882 ; and ibid. xvi. p. 2633. . 



■• PMl. Mag. 1884 (5), vol. xviii. p. 210. i 



» IKd. « Ihid. p. 214. \ 



