Thermodynamic Properties of Air. 11 



curve, it is 14° 94. Therefore final temp. = 17°*55, total rise 

 of temperature of the gas =101*49 + 17*55 = 119°*04. 



According to Bartoli and Stracciati the specific heat of 

 water at the temperature of the experiment is 0'9996, the 

 sp. heat at +15° being taken as unity. Therefore we have 

 finally : 



253*829 x 0-9996 x 5*430 = q x 48*8342 x 119*04, 



whence it follows : c x = 0*2368 as the mean value of the 

 specific heat of air between the limits —17° and +100°. 



§ 10. In the annexed table I have collected all the data 

 serving to characterize the different determinations of the 

 specific heat of air at constant atmospheric pressure. The 

 columns headed I.— XI. contain the following quantities : — 



I. Mass of air passed through the calorimeter in grs. 

 II. Equivalent mass of calorimeter in grs. of water. 



III. Velocity of current : grs. per min. 



IV. External heating of calorimeter, before and after the 



current, in r—^ degr. per min. 

 Y. Time of influx of heat into the calorimeter in minutes. 

 VI. Initial and final temperatures of calorimeter (corr.). 

 VII. Total rise of temperature (corrected). 

 VIII. Difference of temperatures of heater and gas, as indi- 

 cated by the galvanometer (degrees). 

 IX. Initial and final temperature of the gas (degrees). 

 X. Specific heat of air, under a pressure exceeding slightly 

 the atmospheric, between temperatures indicated 

 in IX. 

 XI. Mean values of the foregoing. 



The whole of these results maybe summed up as follows: — 



Between + 20° and +98° Cl = 0*2372 



- 77° „ +16° Cl = 0*2374 



„ -102° „ +17° Cl = 0*2372 



„ -170° „ +18° d = 0*2427 



On the ground of these results we may assert with certainty 

 that the specific heat c x does not vary in a sensible manner 

 down to a temperature of about —100°. At the lowest 

 temperatures, however, there is apparently a small increase 

 in the quantity ci of about 2 per cent. But I think there is 

 sufficient reason to conclude that even this small increase is 

 only apparent, namely, that it ought to be ascribed to the 

 influence of pressure rather than to that of the temperature. 

 Phil. Mag. S. 5. Vol. 42. No. 254. July 1896. C 



