(421 ) 



Only a small number of points having been given, and the densities 

 being small, as \vas obserxed before, C'a cannot be determined with 

 snfticient a('<'ui'ac*y. We borrowed the values of this coefticient from 

 Comm. No. 71 § 3, where 6a„ = 0.0„G7() and 6a,„„ = 0.(),6()6. 



In order to determine the course of the y>rA curves more accurately 

 the value of in\\ was chosen for a density corresponding to that in 

 the hydrogen thermometer of Comm. No. GO with which (comp. 

 Comm. No. i)?^ XV § i) ().()()3G()2il ^^as found for the pressnre 

 coefticient for hytU'Ogen at 1090 mm. zero point pressure. By successive 

 approximations this value of j^/t'A i^ to be derived b}' means of these 

 determinations of isotherms. We tind for 0°: 



pVAi)° A 100 mm. = 1.000256 



and for 100'. 20 with the pressure coefticient 0.0036629 : 



pf^A ioo°.2 = 1.367373. 

 For the density (^/a = 1.44 may be put in both cases. 

 Now we obtain live values oi' pvA and cIa for 0^ and four for 100 '.20, 

 from which by the method of least squares the coefficients ^4a and 

 JjA of equation (1) may be determined. These values are : 

 For 0°: 



^A= 0.99924 

 5a= 0.5800 X lö~-^ 

 For 100^20: 



Aa— 1.36626 

 ^A = 0.8632 X 10~'. 

 For 100^00 we may calculate from this : 

 Aa= 1.36553 

 ^A= 0.8626 X 10-\ 

 The differences which remain between the values of /)6'a of table I 

 and those calculated according to formula (1) with tlie coefficients 

 found here are respectively : 

 for 0^-- : 



+ 0.00018, — 0.00023, — 0.00028, + 0.00004, + 0.00029 



for 100".20 : 



— 0.00013, -f 0.00034, — 0.00001, — 0.00019. 



The first value always refers to the point calculated for the 

 hydrogen tliermometer. The differences are slight, and do not or 



only very slightly exceed -— of pvA • 



