338 



REPORTS ON THE STATE OK SCIENCE. 



following table gives the specific heats of CO2 accoi'ding to diffefent 

 observers at 0° and 100° C. : — 



The value of the mean specific heat at constant pressure from 10° to 

 100" C. deduced from Joly's experiments at constant volume is 0-2120, 

 ■which is nearly 5 per cent, higher than liegnault's value at this tempera- 

 ture, but agrees as closely as can be expected with that found by Swann. 

 The variation of the specific heat with density observed by Joly agrees 

 very closely with that calculated by Callendar ^ from the experiments of 

 Joule and Thomson on the cooling efiect in expansion through a porous 

 plug. 



The rate of increase of the specific heat between 20° and 100° C. 

 observed by Swann is nearly a mean between the rates given by Regnault 

 and Wiedemann, but is much larger than that found by Holborn and 

 Henning, or deduced by Langen from explosion experiments. It is 

 probable that the variation is not linear, but that the rate of increase 

 diminishes with rise of temperature, as indicated by Mallard and 

 Le Chatelier's formula, which would make the specific heat a maximum 

 at 1700° C. The latter formula differs from Holborn and Austin's by 

 more than 20 per cent, at 800° C. The explanation appears to be partly 

 that Regnault's value for the rate of increase at 100" C, adopted by 

 Mallard and Le Chatelier, is too high, but chiefly that Holborn and 

 Austin's values, as already explained in the case of air, are systematically 

 too low, and that the error increases with rise of temperature. 



Specific Heat of Steam. 



5, Ee^oault's value 0-475 for the specific heat of steam at atmo- 

 spheric pressure over the range 125° to 225° C. was obtained by taking 

 the difi'erence between the total heats of steam, superheated to these 

 temperatures, as observed by condensing the steam in a calorimeter. 

 Since the diflerence, corresponding to 100° superheat, is only i':ith of the 

 total heat measured in either case, it is evident that the method might 

 oive rise to large errors. For this reason many writers have preferred 

 to deduce the specific heat of steam theoretically in various ways from 

 Regnault's value of the rate of change of the total heat of saturated 

 steam, namely, 305 cal. per 1° C, which, however, really involves the 

 same source of error in an aggravated form. Thus Zeuner gives 

 S = 0-568 ; Perry,2 S = 0-306 at 0" C. to 0-464 at 210° C. ; Grindley =• 

 0-387 at 100° C. to 0665 at 160° C. 



A direct measurement of the specific heat of steam by the continuous 

 electric method gave S = 0-497 at 108° C* Subsidiary experiments, in 

 conjunction with Professor Nicolson,^ by the throttling calorimeter method 



' Phil. May., January 1903, p 

 « Phil. Trails., 1898 



rs, '' Steam Engine, 1899, p. 582. 



* Callendar, Proe. U.S., 1900. 

 « "McGill College, 1897. 



