8 PROPERTIES OF STEAM AND AMMONIA 



measurements. Callendar * has expressed the opinion that the Holborn 

 and limning values are too low by as much as 10 per cent. 



Knoblauch and Jakob.f and subsequently Knoblauch and Moiling 

 made observations of the specific heat at four different pressures, 2, .), <>. 

 ami 8 kg. per sq. cm. The latter exprriinmts extended the temperature 

 range of the former from 35O-55 C. 



viewing all the experimental evidence one must be convinced 

 that for the range of tempi r. it m e covered, the Knoblauch and Mollier 

 measurements should be accepted without modification. These are 

 shown in I itf. 3. For convenience in the identification of the measure- 

 ments associated with the four pressures employed, the points have been 

 separated into four group 



By a combination of the characteristic equation (B) and the Clausius 

 relation a general equation for the specific heat c p may be derived. From 

 the equation 



'-<-y-(' + 3*/>>)f;' 



the second derivative 



is obtained. Hence, from the Clausius relation, 



n+i), 



/r 

 An integration with T constant gives an expression for c f , namely 



The arbitrary function F (T) is evidently c^, that is, the specific heat 

 at zero pn This was taken as a constant by Callendar. The 



experiments of Knoblauch and Mollier show that c^ cannot be constant, 

 and this conclusion i^ confirmed by the high- temperature experiments of 

 Langen and others. It has been suggested that a simple linear relation 



c*=a+ fiT 



may be assumed, but it is found that better results are obtained by a 

 relation of the form 



Writing the equation for c, in the form 



values of the term/(/>, T) may be calculated for each of the Knoblauch 

 and Mollier experiments, and by subtraction the corresponding values of 



Report of British Anoc. Committee on Gaseous Explosions, pp. 31, 32 (1908). 

 \ Mittefl. Qber Forachungwrbeit, Vol. 35, p. 109. 

 tZeit.de.Ver. deuuch. Ing., VoL 55, P. 665 (191 1). 



