88 K. D. Kraevitch on an Approximate Law of the 



it is impossible, in my opinion, to make any true conclusion 

 from the magnitude of c — c x . 



If the temperature T be determined with sufficient accuracy, 

 then both methods used for calculating it give one and the 

 same result, just as they do for r and c — c^ If, on the con- 

 trary, we purposely take an incorrect, but more or less likely 

 value for T , then it gives dissimilar results. This shows that 

 the above enunciated theory has a firm basis and gives a right 

 to hope that the values found for r and c — Ci deserve greater 

 confidence than those given by calorimetric methods. 



It would be very important in relation to the confirmation 

 of our proposed theor} r to prove experimentally or theoretically 

 the truth of its fundamental proposition — that vapours in a 

 state of saturation subject themselves to Boyle's and Gray- 

 Lussac's laws. The only existing means of doing this, 

 namely the formula 



1 r 



V—IV= -r 



A'dp y 

 alt 



cannot, however, be made use of, because the quantity r cannot 

 be considered as determined with sufficient accuracy by ex- 

 periment. Besides which this quantity has been measured at 

 different pressures for only a very few liquids ; in the case of a 

 very few of which is it possible to calculate to owing to the 

 coefficients of expansion being unknown at high pressures. 

 I applied the preceding formula to aqueous vapour, and made 

 use of Zeuner's Tables, in which the value of A(v—w)p is 

 given for various temperatures : I added Awp corresponding 

 to the same temperatures, and divided the sum by AT. The 

 figures thus obtained present the expression 



pv 



Y > 



which, with a small variation of temperature (20°— 40°) on 

 either side of T , should not vary within the limits of experi- 

 mental errors. Unfortunately, the figures so obtained were 

 so irregular that it was impossible to come to any rational 

 conclusion from them. 



At temperatures remote from T the results given by equa- 

 tion (5) sometimes differ from the data given in tables. 

 From this it should in no way be concluded that the bases 

 of this formula are false. It only indicates that the vapour 

 under consideration diverges on one side or another from the 

 laws of Boyle and Gay-Lussac at temperatures remote from 

 T . Some vapours preserve the properties of a perfect gas 



