1882.J On the Critical Point of Mixed Gases. 113 



IX. ''On the Critical Point of Mixed Gases." By GERRARD 

 Ansdell, F.C.S. Communicated by Professor James 

 Dewar, M.A., F.R.S. Received June 8, 1882. 



Having on two previous occasions communicated to the Society 

 papers on the physical constants of liquid hydrochloric acid gas and 

 liquid acetylene, under which head I include the coefficients of compres- 

 sion and expansion, the critical points, and the volumes and tensions of 

 the saturated vapour, it naturally led up to what promised to be a long 

 investigation into the similar constants of other gases ; and, amongst 

 other things, the behaviour of two or more gases in presence of each 

 other, more particularly with regard to the alteration of the critical 

 point, appeared to me of especial interest. 



These experiments, which I commenced nearly two years ago, were 

 unavoidably interrupted at the time, and I have only now been able to 

 resume them. 



This subject has latterly engaged the attention of many physicists 

 and chemists, and, amongst others, both Andrews and Cailletet have 

 examined to a certain extent the behaviour of gaseous mixtures, 

 the former finding both the critical point and vapour- tension of 

 carbonic acid considerably modified by the introduction of a small 

 quantity of pure nitrogen, and the latter (" Compt. Rend.," 90, 210) 

 noting the peculiar behaviour of carbonic acid with one-fifth its 

 volume of air, the former appearing to mix completely with the latter 

 at 130 atmospheres pressure and 5° - 5 C, forming a homogeneous 

 mixture. More recently Amagat (" Compt. Rend.," 89, 1879) and 

 Roth (" Wiedemann," N.F., 2, 1880) have contributed exhaustive 

 papers on the deviation of gases from Mariotte's law. Clausius 

 and Van der Waals have introduced new formulas for calculating 

 the critical point, Winkelman (Berichte, N.F., 2, 1880), Hannay 

 (" Proc. Roy. Soc," vol. 33) and others have been examining the rela- 

 tion between the different states of matter, and Ramsay and Pawlewski 

 have investigated the behaviour of different liquid compounds with 

 regard to their critical points, &c. ; the former took equal weights of 

 pure benzene and ether, and found that the critical temperature and 

 pressure of the mixture was just between those of the individual 

 bodies, but as he evidently experimented with only the one mixture, 

 his results do not bear much upon the present problem, for which 

 these experiments were undertaken, namely, the variation of the 

 critical points of different percentage mixtures of two or more gases. 

 Pawlewski's results, which seem to have an important bearing on the 

 subject, I shall refer to more fully afterwards. 



Before selecting any particular gases for investigation, there were 



VOL. XXXIV. I 



