ON GASEOUS EXPLOSIONS. 839 



enabled the variation of the specific heat with pressure to be calculated. 

 These gave the formula 



8, = 0-478 + 0-0242 p (373/^) ^« (Callendar) 



where p is the pressure in atmospheres. The approximate constancy of 

 the limiting value 0-478 of the specific heat at zero pressure over' the 

 range 0° to 200° C. was verified by calculating the corresponding values 

 of the saturation pressure, which were found to agree accurately with 

 Regnault's observations over the whole range. The theory was also 

 verified by a measurement of the ratio of the specific heats of steam by 

 Makower,' which gave values 1-303 to 1-307, agreeing closely with that 

 deduced by Callendar. 



The experiments of Lorenz,^ and of Knoblauch and Jacob and Linde ^ 

 afforded a remarkable verification of the theory of the variation of the 

 specific heat with pressure. They found the specific heat at 1 atmo. 

 to be practically constant over the range 100° to 300° C, but their value, 

 namely, 0-463, is decidedly lower than Regnault's. 



Holborn and Henning,'* in their experiments on the specific heat of 

 steam at atmospheric pressure, improved Regnault's method by employ- 

 ing an oil calorimeter at 110° C. so as to avoid condensing the steam in 

 the calorimeter. They determined the ratio of the specific heat of steam 

 to that of air by passing currents of air and steam in succession through 

 the apparatus under similar conditions, and obtained the following values 

 of the ratio for different intervals of temperature : — 



Temperature Interval . 110°-270° 110°-440° 110°-6-20° 110° -820° 

 Batio/Steam : Air . . 1-940 1-958 1-946 1-998 



In their subsequent series with a platinum heating-tube at higher 

 temperatures they obtained the following ratios : — 



Temperature Interval . il.5°-S2G° 115^-1180° 115°-1324° 

 Katio/Steam : Air . . 1-900 1-973 2-003 



The second series appears to make the ratio about 5 per cent, lower 

 at 110°-820° than the first, wh ch suggests the possibility of constant 

 errors depending on the type of apparatus employed or on the velocity 

 of the gas-current. The experiments of Callendar and Swann would 

 make the ratio 2-05 at 100° C, which is higher than any of the values 

 obtained by Holborn and Henning at 1400° 0. 



Holborn and Henning point out that their results at 1400° C. 

 cannot be reconciled in the case of steam and COj with any of the 

 results of explosion methods. They are 6 per cent, to 13 per cent, lower 

 than Langen's, which are among the lowest. But having regard to the 

 fact that the constant- pressure method which they employed appears to 

 give results so much lower than Joly's or Callendar's methods at ordinary 

 temperatures, and that the experimental difiiculties increase so greatly 

 at higher temperatures, it does not seem at all improbable that a 

 considerable part of the disci'epany is to be attributed to .=iystematic 

 f'rrorK of the constant-pressure method, 



! Phil. Mat}., February 1901!, 

 * Forsoh. Vet'. Beut. Ing.., 21, 190o, p. OH. 

 ' Loc. cit., pp. 1 and 3.5, 1906, p. 109. 

 ' iitn. P?iy.i. xviij. 1905, p. 739. 



