Vapour-pressure and the Volumes of Vapour and Liquid. 135 



Here it must be remarked that the values takeu by the quan- 

 tities IT. TT, and v: at the critical temperature, at which \ = 0, 

 and which values may be denoted by LT C , ~W C , and io c , can be 

 obtained from the expressions above mentioned, contained in 

 § 3 of my previous paper, if the series contained in § 4 be also 

 taken into account, as follows: — 



n c =^; W c =2 7 ; w=2 y (6) 



These three values can hence be regarded as determined, just 

 like the value C , directly by the constant y; and accordingly 

 the following fractions can be formed: — 



n w , w 



^r-j ^, and — 

 n c T\ J ic c 



It is these fractions whose values are given in the Table 

 (p. 133) by the side of the corresponding gradually increasing 

 values of the fraction © C denoted by 0. 



§ 2. In the foregoing Table is exhibited a relation, equally 

 holding true for all substances, of the quantities 17, W, and w 

 to a temperature-function which is still left undetermined. 

 Now what the form of the relation between those quantities 

 and the temperature itself is, whether and in what degree it 

 also agrees for different substances*, depends on the behaviour 

 of that temperature-function. In my investigation I started 

 originally from the hypothesis that the temperature-function 

 could be represented by an expression containing only one 

 constant, dependent on the nature of the substance; but I 

 found, on closer consideration, that a satisfactory accordance 

 with experiment cannot be attained in so simple a manner. 

 After various comparisons I obtained, as the most suitable 

 form of an equation for the determination of the fraction 

 which we have denoted by 0, C , the following: — 



!=£->. (J) 



c 



* Two older propositions on this relation I have long since discussed 

 (Pogg. Ann. lxxxii. p. 273, 1551, and Abhandlungensainmlung. i. p. 119, 

 1864 i. If, namely, the temperatures which with different liquids belong 

 to equal vapour-tensions be called corresponding temperatures, then, accord- 

 ing to Dalton, the differences between corresponding temperatures are equal. 

 Groshans, on the other hand, has set up an equation (Pogg. Ann. lxxviii. 

 p. 112, 184.9) which, supposing that the temperatures be reckoned from 

 — 273° C, expresses that for any two liquids all corresponding tempera- 

 tures are proportional. Of these two propositions the second certainly 

 does not deviate so far from experience as the first, but still it deviates 

 too far for it to be possibly admitted as expressing an actual physical law. 



