254 Mr. J. Rose-Innes on the Theory of 



- A careful determination of the increase of pressure .of 

 hydrogen at constant volume from the freezing-point to the 

 boiling-point has recently been made by M. Chappuis 

 (Travaux et Memoires du Bureau International, tome vi. 

 p. 108 ; see also Everett, C. Gr. S. System of Units, p. 115). 

 The pressure at the freezing-point was 1 metre of mercury, 

 and the increase of pressure was '366254 of a metre of 

 mercury. If we could treat hydrogen as a perfect gas we 



should therefore obtain .,„,.,-. r . or 273 o, 034 as the absolute 

 •366254 



value of the freezing-point. 



But it is of course necessary to inquire how far we need a 

 correction .owing to the deviation of hydrogen from the lawg 

 of a perfect gas ; for this purpose we take the equation 



'Divide by ft and we have 



dt\t r 'dpUv/tf 2 \dvj t t 2 ' 



Let the suffix refer to the freezing-point, the suffix 1 to 

 fhe boiling-point, and integrate the above equation with respect 

 to t between the limits t and t x . We obtain 



pi _ Po _ _ f '• JK d* r d p) & _ C ti (d± v dt 

 h t j to 'dpVdvJte x\dv ) t e 



where M is some mean value of JK,— -{ -f ) and N is some 



/(fylr\ Op\dv)t 



mean value of ( -P- h. Hence 



that 



p.-M-N = po-M-N = Pl - P<i 

 H to ^i — to 



i0= /^M=_N ((i _ g 



Pi—Po 



Pi-Po Pi-Po 



The expression Po (h — t ) gives us the value of /<, when 

 P\~ Po 



