ON GASEOUS EXPLOSIONS. 315 



systematic errors in their method of experiment which may become 

 important when it is applied to higher temperatures. It may be take n 

 as fairly certain that the volumetric heat of air at 100^ C. is withi d 

 2 per cent, of 4-9. 



In the case of CO2 the results obtained by Wiedemann and Regnault 



were : — 



W R 



Increase of internal energy to 100 710 680 



„ ., „ „ to 200 1510 1490 



„ „ „ „ 100 to 200 800 810 



The first two rows of figures represent practically the quantities 

 actually measured in these experiments.' The third is obtained by 

 difierence from the first two, and is therefore affected with a greater 

 probable error than either. The result of the two sets of experiments 

 may be summed up by saying that the volumetric heat of COj at 100° C. 

 taken a.s equal to the mean volumetric heat between 0° and 200° C. is 

 between 7'45 and 7 '55, and that its rate of increase with temperature is 

 between 0"009 and O'OIS, or roughly one six-hundredth part per ° G. 

 The specific heat of steam at constant (atmospheric) pressure in the 

 neighbourhood of 100' C, according to Regnault, is 0'48, equivalent to 

 6 '64 volumetric heat, and subsequent observers have shown that this 

 value is at least as accurate as Regnault's value of the specific heat 

 of air. 



From Joly's experiments Avith the steam calorimeter, when corrected 

 according to Callendar for the error in Regnault's value of the latent heat 

 of steam, the specific heat of CO2 between 10° and 100° C. and at a 

 pressure of 12 atmospheres is 0*172 and it increases by about 0-25 per 

 cent, per atmosphere. Assuming this law of increase to hold between one 

 atmosphere and 12 atmospheres, the mean specific heat at normal density 

 for the range 10° to 100° should be 0-1666, and the volumetric heat 

 should be 7 "3, which is again decidedly greater than the values obtained 

 by Wiedemann and Regnault. According to a recent determination by 

 Swann, the result of which has been communicated to the Committee by 

 Professor Callendar, the volumetric heat of CO2 at 100° is 7 "76 — again 

 materially higher than Regnault and Wiedemann (7"5). 



Holborn in conjunction with Austin carried the constant-pressure 

 determinations for air and COj up to 800° C.^ The gas was heated 

 electrically and the temperature was measured with a thermo-couple. 

 Similar measurements on steam were made by Holborn and Henning, 

 who subsequently carried the determinations for the three gases up to 

 1400° C.3 



Holborn and Henning express the results of all these experiments in 

 algebraical formulas representing the mean specific heats of CO2, air, and 

 steam respectively over the range 0-^ in the case of the first two gases, 

 and 100-t) in the case of steam. From these formulse the full-lined 



' The lower limit of temperature in Kegnault's measurements was 10°, the upper 

 limits were 100° and 210° respectively. In Wiedemann's work the lower limit was 

 25° and the upper 100° and 200° respectively. The results have been reduced to 

 the forms here given on the supposition that the volumetric heat between 0° and 

 25° is 6-6, and at 200° 7-4. For the small additional range of temperature required 

 these figures are certainly as accurate as the experiments. 



^ Wisg. Abhandlu)igen der Phys. Techn. Reiehsanstalt, 1905. 



' Ann. d. Phys., 23, 1907, p. 809. 



