Mixtures of Ethane and Nitrous Oxide. 179 



still : the increase of pressure was 0*43 atm. at the same 

 temperature "*. 



15. The critical temperature of the gases was determined 

 very carefully : as with the mixtures, a stirring-rod had been 

 put within the tube, and so the determination could be con- 

 ducted according to the principles explained in the account of 

 my observations with0O 2 t. The critical temperature for the 

 two samples of ethane amounted to 31°*95 C. and 32°05 C. 

 respectively. This would point to a critical temperature of 

 + 32°* 3 for pure ethane. By admitting a little air (^ to ± 

 per cent.) into the last tube the increase of pressure at 20° 0. 

 rose to 2*7 atm., i. e. more than six times the former value ; 

 while the critical temperature had gone down to 31 0, 25 C. 

 This would point to ±32°*2 C. as the real critical temperature 

 of ethane. The admixture in my ethane seems to lie far 

 below 0*1 per cent. 



16. It is not impossible that, in filling the tubes, a little 

 air remains in the gases, because they have to pass through 

 some long tubes connected with joints before entering the 

 experimental tube, and the air has to be expelled by means of 

 exhaustion. I might probably have got a still purer gas by 

 filling the tube more directly, but I preferred to apply exactly 

 the same method which I used in preparing the mixtures, in 

 order to be warranted against mistakes resulting from differ- 

 ences of purity. 



17. The critical temperature of ethane as determined by 

 former observers is somewhat higher. Dewar % gives 35° C, 

 Olszewski § 34° (1, Haenlen || from 32° C. to 40° C, probably 

 34°"5 C. In his experiments retardation has played an 

 important part, and his gas cannot have been very pure ; 

 otherwise one finds a definite critical point, not a critical 

 region as he does. He prepared the gas by the method of 

 Gladstone, Tribe, and Franklandlf from C 2 H 5 I. Olszewski 

 obtained ethane from C 2 H 5 Zn. Both Haenlen and Olszewski 

 purified the gas by cooling and boiling at a low temperature. 



1 cannot tell w r hat the reason is of this discordance between 

 the values for the critical temperature. Perhaps it has some 

 connexion with the different ways of preparing the gas. I 

 am going to repeat the experiments with ethane prepared 



* Andrews, in his famous experiments on carbonic acid, observed an 

 increase of pressure of more than two atmospheres in a similar case. 

 • t Kuenen, Kon. Akad. Amsterdam, 29 Oct. 1893, pp. 85-90 ; Com- 

 munications, &c, No. 8, pp. 11, 12. 



X Dewar, Phil. Mag. [5] xviii, p. 214. 



§ Olszewski, Bulletin Ac. des Sciences de Cracovie, 1889, p. 27. 



|| Haenlen, Lieb. Ann. eclxxxii. p. 245. 



5J J. Chem. Soc. xlv. p. 154 j xlvii. p. 236. 



