120 



Mr. G. Ansdell on the 



[Jan. 29, 



In this table 



A = temperature of gas. 



B= volume of the saturated vapour at point of liquefaction. 

 C=fractional volume of the gas at point of liquefaction in relation 

 to the initial volume under one atmosphere of pressure. 

 D = volume of the condensed liquid. 

 E= ratio of volume of gas to that of the liquid. 

 F= pressure in atmosphere. 



The critical point was found to be 51°*2'5 C. 



It will be seen from this table, that the volumes of the saturated 

 vapours and liquid gradually approach each other as the temperature 

 nears the critical point, and would undoubtedly become identical, if 

 the experiments could be carried on up to the critical point. The 

 following curves, the first of which represents the change of volume 

 of the saturated vapour and liquid, in relation to the temperature ; 

 and the second the ratio between these volumes in relation to the 

 temperature (column E in the table) show these results in a graphical 

 form. 



Curves. 



The ratio between the volume of the saturated vapour and the 

 volume of the liquid at different temperatures decreases very regularly 

 until within about three degrees of the critical point, where a singular 

 point in the curve occurs, and the ratio approaches unity with great 

 rapidity. The volume of the liquid increases very regularly up to a 

 temperature of about 48° C, and at 51° C, or within 0*25 of a degree 

 of the critical point, the distinction between the saturated vapour and 

 the liquid vanishes, as although liquid is plainly seen to condense on 

 the surface of the mercury, on increasing the pressure the line of 

 demarcation immediately disappears, and it is impossible to say whether 

 the tube is filled with the saturated vapour or the liquid itself ; there- 

 fore no results could be obtained nearer the critical point than about 

 a fourth of a degree. 



Avenarius, in a paper intitled " The Causes which determine the 

 Critical Point" ("Mem. Acad. Sci. St. Petersbourg," 1876-77), made 

 a number of experiments on ether, and came to the conclusion that the 

 volumes of the saturated vapour and of the condensed liquid at the 

 critical point were not identical. He was under the disadvantage of 

 working at a very high temperature, the critical point of ether being 

 192° "6 C, which must have been very dim cult to keep fixed within 

 half a degree. 



My own experiments, which were carried out at a very much lower 

 temperature, and were consequently capable of greater accuracy, on 

 account of the facility with which the temperature could be kept con- 

 stant to within -^th. of a degree, appear to confirm his results, in so far 



