284 



Mr. S. Skinner. 



[Apr. 21, 



was constructed so that it could be filled to a certain mark under 

 atmospheric pressure and at the temperature of the room. This- 

 being filled alternately with PH 3 and HC1, was discharged into a large 

 glass tube. In this way I prepared a mixture of equal volumes of the 

 two gases. Part of this was delivered into a Cailletet tube which was 

 set up in one of the iron bottles of a Cailletet pump ; in the other 

 bottle was placed a well tested air gauge. 



The temperature of the tube was maintained constant by a vapour 

 jacket of acetone, and altered by varying the pressure under which the 

 liquid boiled. 



Observations were then taken for isothermals. The following, a& 

 useful for the present purpose, are extracted from those readings ; the* 

 whole mass of the gas used being 18'0 c.c. at 0° and 760 mm. 



Temp. Saturated vol. 



7° — 



13 0*84 c.c. 



18 0-64 „ 



21 0*47 „ 



24 0*37 „ 



28-5 0-275,, 



45 0-102,, 



Pressure. 



11 



6 



19 



3 



27 



3 



33 



6 



39 



1 



47 



2 



85 



3 



The critical point of the liquid was observed at 48° C. and under 

 95 atmospheres. 



The temperature at which the crystals are formed under one 

 atmosphere pressure is given as —30° by Ogier. 



The formation of these crystals is evidently a dissociable one, for 

 when the pressure is removed they decompose into equal volumes of 

 the separate gases. The question whether any chemical combination- 

 takes place before the appearance of crystals is one we shall discuss- 

 when considering the saturated volume curve of PH 4 C1 in comparison 

 with those of its constituents. 



Experiments on Phosphine. 



This gas, prepared and dried as before, was passed for some hours 

 through a Cailletet tube from which the air had previously been 

 displaced with carbonic acid gas. After careful sealing the tube was 

 placed in the iron bottle, and liquid was readily obtained at the 

 ordinary temperature under a pressure of about 30 atmospheres. 



The critical state was reached with this liquid at 54° and 70'5 

 atmospheres pressures ; so that it is easily observed when the tube is 

 heated with acetone vapour. It is interesting to compare this critical 

 point with that of the nitrogen analogue, ammonia, which does not 

 reach the critical state till 130° and 115 atmospheres pressure. This 



