222 



This equation nut only represents all our observations as well as 

 possible; but the agreement with Schalkvvijk's results appears to be 

 even better than for the provisional calculation, which is seen from 

 the following table. 



30 

 40 

 50 



1.0935 1.0936 +0.0001 

 1.1009 1.1010 i.-f 0.0001 



1.1085 I 1.1086 



+0.0001 



The tinal equation may therefore be considered to represent the 

 whole region of the isotherm below 1000 alms. The agreement with 

 Schalkwijk is perfect up to Z) = 100, which corresponds with a 

 pressure of 115 alms. Reversely it appears therefore that we may 

 extrapolate up to ±120atms. from the equation at which Schalkwijk 

 arrixed from his observations from 8 to 60 atms., viz. 



PV= 1.07258 + O.O3667I/J + 0.06993 i;^ 



At /J — 200 or P=i2bO atms. the error which would 

 then be made, becomes ab'cady 3 per 1000. For greater densities 

 up to Z) = 500 the number of virial coefficients 3 is too small. It 

 must then be 4 at least. It will not do simply to add a 4"^'' coeffi- 

 cient to Schalkwijk's equation, which appears from the deviations, 

 which (see table) are now positive, now negative. 



§ 2. Compurison of the observation.'^- at J 5''. 5 with Amagat's. 



We have one series of observations with 4 data below J 000 atms. 

 and three above it at our disposal. (See p. 215). 



An equation has been calculated from the 4 data below 1000 as 

 a control of the observations at ± 100 atms. (See preceding com- 

 munication). To compare our data with those of Amagat at 15°. 4 

 we have calculated an empiric equation with 6 virial coefficients 

 from 6 observations. In the seventh observation at 383 atms. we 

 ha\'e then a control. 



