438 MR. J. H. BRINKWORTH ON THE SPECIFIC HEAT OF STEAM, ETC. 



Comparison of the Result with Theory. 



The values of the specific heat at constant pressure can be deduced from equation 

 (7), and this relation has been used in order to compare my value of the specific heat 

 with values obtained by other observers. Assuming the linear variation with 

 temperature, as experimentally determined, my own observations give the value 0'4878 

 as the specific heat at 100 C. Substituting this value in the above equation we 

 find S = G'4634. 



The values of the specific heat at atmospheric pressure and at various temperatures 

 can then be calculated and the mean value over any desired range deduced. Over 

 the range 110C. to 230 C. the mean value is thus found to be 0'47G. From 

 equation (5) the following'expression showing the variation in the total heat of steam 



can be derived 



F-F = So(0-0 )-(n 



Assuming 640'3 calories as the value of the total heat at 100 C. we find the latent 

 heat at C. to be 5967 cal./gr. which is in good agreement with that found by 

 DIETERICI. The above values of S and L may be used to calculate the saturation 

 pressures of steam. The agreement found between the calculated values and those 

 determined experimentally is exceedingly good, especially at low temperatures when 

 the value of S is approximately constant. For example, the calculated pressures at 

 C. and at 60 C. are 4'585 mm. and 149'23 mm. respectively, the experimental 

 values at these temperatures are at G. 4'600 mm. (!{EGNAULT) and at 60 C. 

 148'80 mm. (REGNAULT). 



Comparison of this Result with the Work of other Observers. 



On pp. 397-399, Prof. CALLENDAR has discussed the work of other observers. The 

 value of the specific heat at 108 C. deduced from my experimental measurements is 

 2'0230 or 0'484 with the calorie as the unit. 



In fig. 10 I have plotted the values of /^obtained by Prof. CALLENDAR against the 

 corresponding values of D. The points line about a straight line which practically 

 coincides with that obtained from my measurements with the non- vacuum, non-silvered 

 calorimeter. Apparently there is no systematic difference in the values of hfcm 

 obtained with the silvered and unsilvered calorimeters respectively. When con- 

 sidered, together with the results of my own experiments with various pressures in 

 the vacuum jacket, this concordance indicates that in the many calorimeters, evacuated 

 by the makers, which have been used, the vacua produced were far from perfect. It 

 is again of interest to note that in Prof. CALLENDAR' s experiments similar absurdly 

 low values of the specific heat were obtained when attempts were made to mix the 

 steam by means of wire gauze. 



