140 Prof. R. Clausius on the Theoretic Determination of 



For this, by introducing new constants, we can write more 

 briefly 



i=AT-»-B; (10) 



and thereby (3) is transformed into 



JL = J__ AT - ra - B . . an 



KT r-« (v + /3f V ; 



The values of the constants A and B for ether are obtained 

 from the above-given values of a, b, and y as follows: — 



A= 15-607; B = 0-0044968. 



§ 4. The substances in which it has not yet been possible to 

 extend the observations of the vapour-tensions up to the cri- 

 tical temperature, present difficulties, in the determination of 

 the constants a, b, and n in equation (7), which are the greater 

 the more distant the highest observed temperature still is from 

 the critical temperature. If, namely, that distance is very 

 great, the alterations of the constants which, in the tempera- 

 ture-interval for which observations are available, occasion but 

 slight differences in the calculated vapour-densities, yet have 

 for their result a considerable difference in the calculated cri- 

 tical temperature and the pressure corresponding to it. 



To these substances belongs water. I have tried, from Reg- 

 nault's observations of tensions, which extend to somewhat 

 above 220°, to deduce the most probable values of the con- 

 stants, and, after various comparisons, have arrived at the 

 following numbers: — 



a = 5210; 6 = 0-85; n = l-24. 



With the aid of these numbers, and on the supposition that 

 for the temperature of 100° the vapour-tension amounts to 1 

 atmosphere, I have, as in the case of ether, deduced the vapour- 

 tensions for a series of temperatures advancing by increments 

 of 20° each, and found the following values. So far as the 

 observation-values extend, I have added them also, for com- 

 parison, selecting those values which Regnault took direct 

 from the curves constructed by him, and which he regarded 

 as the most immediate result of his observations. Where he 

 gives two values, obtained from different curves, I have taken 

 their mean. Beneath the observed tensions are placed the 

 differences from the calculated ones ; and I have moreover 

 given in this Table the calculated values of s, which will be 

 spoken of further on. 



