138 Prof. R. Clausius on the Theoretic Determination of 



fact that Sajotschewsky himself, by means of an empiric 

 formula deduced from the rest of the observation-values, has 

 determined the tension at 180° to be 3P56 instead of 31-90, 

 whereby the difference from the value derived from our Table 

 is reduced from 0*49 to 0*15. 



The values of TV/TV C and w/w c , as well as those of TI/IT C , 

 are given in our Table. 



In order to deduce the values of TV and w from these fractions, 

 TV C and w e and consequently, according to (6), the constant 

 7 must be known, for the determination of which the constant 

 R is again requisite. The latter is obtained in the following 

 manner: — The quantity R is, in accordance with its significa- 

 tion, inversely proportional to the specific gravities possessed 

 by the substances in the perfectly gaseous state. Now the 

 value of R for atmospheric air is known*, namely 29'27; and 

 from this follows for ether, if d denotes the specific gravity, 

 referred to air, of the vapour of ether in the state of a perfect 

 gas:— 



E=^ (8) 



The question now is, which specific gravity is to be ascribed 

 to ether vapour in the perfectly gaseous state ? That, I believe, 

 can be admitted as such, which is obtained when, in accord- 

 ance with the accepted chemical formula for ether, it is 

 assumed that 1 vol. oxygen and 10 vols, hydrogen, with the 

 corresponding quantity of carbon, give 2 vols, ether vapour, 

 namely the sp. gr. 2 , 5604. On employing this number ford, 

 the preceding equation gives 



R=ll-4318. 



This value refers to 1 kilogram of the substance considered, 

 and therefore, in the present case, of ether; and in it the unit 

 of volume is 1 cubic metre, and the unit pressure the pressure 

 exerted by a weight of 1 kilogram spread over a surface of 

 1 square metre. These units we will retain in the determina- 

 tion of the other constants and the quantities s and a. 

 To determine <y, according to (G) we can put 



J_ _ RTc 



7 ~8n "sp ; (9) 



c c 



and from this, if, employing the values found by Sajotschewsky 

 for the critical temperature and pressure, we put 



T c =273 + 190 = 463 and P c = 36-9 x 10333, 



* See Clausius, Mechanische TJ'annctheorie, i. p. 55. 



