232 Intelligence and Miscellaneous Articles. 



The densities d and d' and the volumes v and v' of the liquid 

 and the vapour, when a mass m of a body in a closed vessel at 

 constant volume is heated, should at all temperatures satisfy the 

 equations 



vd+v'd'=m. 



We have then 



v-\-v'=Y. 

 m — Yd' 



Yd— 



m 



Discussing this expression, the author shows that the meniscus 

 disappears at the critical point if V is the volume of the mass 

 worked with. 



If a mass of a body is subjected to a gradual heating in a volume 

 near its critical one, though a little lower, it will successively reach 

 a condition in which the meniscus disappears ; a condition in which 

 its pressure will be equal to the critical pressure, when its tempe- 

 rature is equal to the critical temperature ; in fine, to a distinctly 

 gaseous state. From the moment at which the meniscus disappears 

 that pressure is no longer independent of the mass. Between this 

 moment and that at which it reaches the critical temperature the 

 body is in a state which corresponds neither to a mass of gas, nor 

 to a mass of vapour and of gas in juxtaposition. It may be re- 

 garded as a mixture or as a solution of the two kinds of matter. 



If the constant volume in which the mass in question is enclosed 

 is equal to its critical volume V, the disappearance of the meniscus, 

 the reestablishment of the level of the mercury in the O tubes, the 

 critical pressure, and the critical temperature should be simul- 

 taneously realized. 



In order to be certain that a body has been brought to the 

 critical state, we must be certain that it offers simultaneously two 

 elements characteristic of this state. The disappearance of the 

 meniscus, and the reestablishment of the level in the capillary 

 tubes taken separately are not sufficient indications, for they 

 may take place outside the critical condition. On. the contrary, 

 equality of the densities or of the specific volumes of the liquid 

 and of the vapour will be a sufficient datum, since it is equivalent 

 to two critical elements. 



In conclusion, in order that the method of heating a body at 

 constant volume shall offer certain indications of the critical con- 

 ditions, the author proposes to perfect it by providing the O tube 

 with a regulator of volume. By suitably modifying the volume 

 by trials the disappearance of the meniscus and the reestablishment 

 of the level of mercury might be obtained at the same instant. The 

 space occupied by the body will then be the critical volume ; on the 

 other hand, the temperature and the pressure will then be also 

 those of the critical point. — Journal de Physique, June 1893. 



