288 



On PhospJwnium Chloride. 



[Apr. 21, 



about 10° the saturated volume of the mixture corresponds to the sum 

 of that of its components, whilst about their critical points the volumes 

 are approximately equal. This shows that at 10° we are dealing with 

 a mixture of the two gases, whilst near the critical point the mixture 

 has combined and the deposition of liquid takes place from gaseous 

 PH 4 C1. 



The volumes which the liquids occupy near their critical points are 

 very nearly equal. This may be shown to be the case in another 

 way. It has been proved from van der Waals' formula that the 

 result of dividing the critical temperature in absolute degrees by the 

 critical pressure gives a number proportional to the greatest volume a 

 liquid can occupy (Dewar, 'Phil. Mag.,' vol. 18, 1884). Now in our 

 case we have — 





T C °C. 



P c . 



T c abs. 













atmos. 







48° 



95 



35 



PH 3 



54 



70-5 



4-6 





52 



86 



3-7 



If then 4*6 volumes of liquid phosphine near the critical tem- 

 perature were brought in contact with 3'7 volumes of liquid HC1 

 about the same temperature, combination would take place with 

 condensation of volume to nearly one half. This is a case of combina- 

 tion of liquids obeying a law very similar to Gay-Lussac's law for the 

 combination of gases under ordinary conditions of temperature and 

 pressure. A symbolic representation of this combination would be : — 



PH 3 + HC1 = PH 4 C1. 

 1 vol. liquid + 1 vol. liquid = 1 vol. liquid. 



A close analogy evidently exists between the law of combination by 

 volume of these liquids near their critical temperatures and Gay- 

 Lussac's law ; whether other cases of such a law of combination will 

 be found is a question which cannot yet be answered. 



Nevertheless the results in this paper appear to me to give answers 

 to these two questions which Ogier states in his essay : — (1) Ce 

 liquide est-il la combinaison meme ou un simple melange des gaz 

 liquefies ? C'est ce qu'il ne m'a pas ete possible d'elucider ; (2) Peut- 

 etre le chlorhydrate d'hydrogene phosphore existe-t-il reellement a 

 l'etat gazeux a une temperature moins basse. 



I hope to continue these experiments with a view to determine the 

 heat of formation of this compound PH 4 C1, and also to determine the 



