some Thermodynamical Relations. 



37 



Substance. 



Pressures from which 

 n was calculated. 



. 50 and 5000 

 . 50 and 5000 

 . 50 and 5000 

 . 50 and 5000 

 . 50 and 800 

 . 100 and 700 

 . 200 and 5000 

 . 10 and 400 

 . 300 and 3000 

 . 150 and 800 

 . 50 and 800 

 . 50 and 800 

 . 50 and 5000 



Value of n. 



1-147 

 1-316 

 1-243 

 1-326 

 1-475 

 1-480 



Carbon disulphide 

 Ethyl bromide . 

 Ethyl chloride . 

 Carbon tetrachloride 

 Bromobenzene 

 Chlorobenzene 

 Chloroform . 

 Ethylene . . 

 Sulphur . . 

 Bromo-naphthalene 

 Methyl salicylate 

 Aniline 

 Methyl alcohol . 



It was found impossible to obtain a constant value for n 

 with dissociating substances when different pressures were 

 employed. 



The whole subject of vapour-pressure is one that cannot 

 well be considered on its own merits, for they must evidently 

 be intimately related to other physical properties ; and although 

 we have already accumulated data for alcohol and ether bear- 

 ing on this subject, we prefer to reserve a general considera- 

 tion of the question until an investigation, as regards the 

 thermal behaviour of other bodies, on which we are at present 

 shall have been finished. 



376 

 235 

 251 

 196 

 517 

 218 

 395 



Part V.* 

 In the first two of the series of papers on " Some Ther- 

 modynamical Relations," published in the Philosophical 

 Magazine (December 1885, January and February 1886), it 

 was shown by one of us that the ratio of the absolute tempe- 

 ratures of nearly related bodies, such as chlorobenzene and 

 bromobenzene, or ethyl chloride and ethyl bromide, is con- 

 stant for equal vapour-pressures ; and that a relation exists 

 between the ratios of the absolute temperatures of all bodies 

 which may be expressed by the equation 



B'^B+c^'-*), 



where R is the ratio of the absolute temperatures of the two 

 bodies corresponding to any vapour-pressure, the same for 

 both ; R / is the ratio at any other vapour-pressure, again the 

 same for both ; c is a constant which may be or a small + 

 or — number ; and t' and t are the temperatures of one of 

 the two bodies corresponding to the two vapour-pressures. 

 * Communicated by the Physical Society : read May 22, 1886. 



