1880.] On the Critical Point of Mixed Vapours. 



539 



pressure of 80 atmospheres, there was a distinct layer of a separate 

 fluid on the surface of the bisulphide, the bisulphide surface however 

 was not so well defined. 



By keeping the temperature at 47° C, on increasing the pressure 

 to 110 atmospheres, the upper surface of the liquid floating on the 

 bisulphide almost entirely disappeared. By reducing the pressure again 

 to 80 atmospheres, the surface of demarcation did not appear, but on 

 reducing the pressure another 5 atmospheres, the line of demarcation 

 again appeared very sharply and remained. A quick withdrawal to 

 58 atmospheres, followed by a gradual increase of the pressure to 85 

 atmospheres, did not make the liquid remain, but on reducing it again 

 slowly to 80 atmospheres the definition became perfectly sharp. 



2. Carbonic Acid and Chloroform. 



Carbonic acid in presence of chloroform at 18° C. liquefied at 25 

 atmospheres, forming a distinct layer on the surface of the chloroform. 

 On further compression, the manometer rose rapidly to 50 atmo- 

 spheres, at which pressure the two liquids mixed completely, after 

 being left for a few minutes. When the pressure was rapidly 

 withdrawn, distinct layers of what appeared to be carbonic acid were 

 always formed, which however became rapidly dissolved in the chlo- 

 roform on standing a few seconds. 



At 33° C. liquid began to appear at a pressure of 35 atmospheres, 

 and on increasing the pressure to 55 atmospheres it behaved in exactly 

 the same way as at the lower temperatures, except that the layer was, 

 if anything, more distinct and mixed more rapidly with the chloroform 

 on standing. 



At 55° C. a layer of liquid was still formed at a pressure of 50 at- 

 mospheres ; at 67° C. it behaved in the same way, except that there 

 was a smaller quantity of liquid formed, and the pressure rose to 

 85 atmospheres. 



In every case it rapidly mixed with the chloroform when left for a 

 few seconds. 



3. Carbonic Acid and Benzol. 



At 18° C. the carbonic acid commenced to liquefy at a pressure of 

 25 atmospheres, and at the moment of liquefaction the surface of the 

 benzol became violently agitated, the carbonic acid falling through the 

 benzol in an oily stream, and becoming completely mixed with it. 



When by further condensation more liquid was formed, the agita- 

 tion almost entirely ceased, the liquid carbonic acid forming a distinct 

 layer on the saturated benzol. On leaving this for about five minutes, 

 the line of demarcation disappeared, and the two liquids formed a 

 perfectly homogeneous fluid. 



