424 Dr. H. Her wig on the Expansion 



sion with constant volume we have the well-known general 

 formula 





Now, from the formula introduced for vapours 

 pv=^{27B + t) 3 



we obtain for constant volume 



\dt/ v v \dtJ v v 



Therefore for vapours 



(*rc+0(g).+* 



that is, considering that pv=(p (273 + t) t 

 ' 273-M /#\ 



1+ ^ Ui, 



273 



273 + t/d<l> 



* 



(£).' 



When 



(^) =0, this value becomes -^-? =0*003663; for 



positive quotients of/ -^-j it is greater. Putting, for example, 



/ = Q0°, and, as before, -7(77) =00004 (corresponding to 



Tables XX. and XXV., of which the values — -. -r--? are now 



to be divided by 1000), we get 



1 + 0-1452 



273-0-1452.90 



= 0-0014. 



Under a pressure of about three atmospheres, to which in the 

 case of sulphide cf carbon this number would belong, Reg- 

 nault* finds for carbonic acid the coefficient of pressure- expan- 

 sion 0-0038. For carbonic acid, according to the formula 



* Mm. de I'Acad. vol. xxi. p. 112. 



