1880.] On the Critical Point of Mixed Vapours. 



545 



On increasing the pressure to 37*0 atmospheres, the mercury appeared 

 in sight with about three-quarters of an inch of a turbid liquid on the 

 surface. On still further increasing the pressure, two distinct layers 

 of fluid were formed, which, however, became quite homogeneous 

 after a short time. On mixing them up by a rapid decrease and in- 

 crease of pressure, the two fluids soon mix. At 28° C, two layers of 

 liquid were distinctly visible at 65 atmospheres, the lower layer being 

 visible as soon as the mercury appeared in sight. 



At 35° C. fluid was condensed on the surface of the lower liquid at 

 80 atmospheres, but when the pressure was increased fco 100 atmo- 

 spheres, the surface of the carbonic acid became undefined. 



At 45° C. fluid is seen to condense on the sides of the tube at a 

 pressure of 100 atmospheres, running down and forming a slight layer 

 on the surface of the camphor liquor, which, however, disappears on 

 still further increasing the pressure. 



When the temperature was 42° "5 and the pressure was suddenly re- 

 duced, the inside of the tube became covered with crystals of camphor. 

 On now increasing the pressure very carefully, the camphor was seen 

 to melt or liquefy and run down the sides of the tube at a pressure of 

 37' 6 atmospheres, and this pressure scarcely increased at all until all 

 the camphor was thus liquefied. 



A diminution of the pressure by two or three atmospheres was suffi- 

 cient to bring out the crystals of camphor. 



At 60° C. the lower layer of liquid still remained, and on increasing 

 the pressure to 100 atmospheres there was an appearance of liquefaction 

 of carbonic acid on the surface. 



Carbonic Acid, Air, and Camphor (third tube). 



A quantity of camphor was placed in the capillary part of a tube as 

 before, which was afterwards filled with a mixture of four volumes of 

 carbonic acid, saturated with camphor vapour, and one volume of air. 



The tube was surrounded with water at 25° C, so as to be far above 

 the critical point of the carbonic acid and air mixture, and on now 

 increasing the pressure the camphor liquefied and ran down the sides 

 of the tube as before. At 50° C. a quantity of liquid, about \ inch 

 long, appeared on the surface of the mercury when it came in sight, 

 the pressure being now 65 atmospheres. 



On leaving the pressure the same, the mercury being just in sight, 

 and increasing the temperature gradually to 60° C, the inside of the 

 tube above the liquid became covered with camphor crystals, which on 

 increasing the pressure another five atmospheres (viz., to 70 atmo- 

 spheres) again dissolves. 



At 65° C, the pressure standing at 70 atmospheres and the mercury 

 and liquid being in sight, on reducing the pressure to 65 atmospheres, 

 the camphor crystals separated out, being again suddenly dissolved on 



