Starkweather — RegnauWs Calorie, etc. 13 



Art. IY. — Concerning RegnauWs Calorie and Our Knowl- 

 edge of the Specific Volumes of Steam; by G. F. Stark- 

 weather. 



The volumes of saturated steam at various pressures custo- 

 marily used are those determined from the latent heats. Since 

 the latter depend almost entirely upon Regnault's experiments, 

 the question of his ' calorie ' is of importance. In calculating 

 the 'heat of the liquid' and 'total heat' Regnault assumed 

 that within the calorimeter range, say from 0° to 30° C, the 

 specific heat of water was sensibly constant. Whether this is 

 so or not depends upon the thermometric scale used. If mer- 

 curial it might be so, but if the scale was that of the air- 

 thermometer, which is the one to which Regnault usually 

 reduced his observations, it certainly would not. 



Bosscha* in 1874 remarked that in the experiments under 

 consideration there was no record of the calorimeter tempera- 

 tures being reduced to the air-thermometer, and accordingly 

 made corrections to Regnault's formula for ' heat of the liquid,' 

 although he still assumed that the specific heat of water was 

 constant within the calorimeter range. To this Regnault 

 replied that the calorimeter temperatures were reduced to the 

 air-thermometer, but as this was over twenty years after the 

 experiments were conducted there has always been more or 

 less uncertainty to many minds. 



The writer hopes to present some evidence from Regnault's 

 experiments themselves corroborating his statement, and will 

 construct formulae taking into account the variation of the 

 specific heat of water from 0° to 30°. The agreement between 

 Rowland and Griffithst regarding this variation is so exact, 

 and their methods were so accurate, that between the limits 

 mentioned it can be regarded as determined. Their results 

 are expressed according to the Paris nitrogen scale, but the 

 specific heats according to Regnault's air-thermometer would 

 not differ qualitatively from them, and ought not to differ 

 much quantitatively. The only person, so far as the writer is 

 aware, who has looked at the subject in the light of recent 

 experiments is Ekholm,J but he concludes (it seems to the 

 writer incorrectly) that Regnault's calorimeter temperatures 

 were not reduced to the air-thermometer, and accordingly 

 makes no corrections for the variation in the specific heat at 

 low temperatures, supposing it to be constant according to the 

 mercurial thermometer. 



* Ann. Phys. und Chem., Jubelband, p. 549. 



+ Phil. Mag., xl, p. 449, 1895, and Proc. Roy. Soc, lxi, p. 419, 1897. 



% Bihang till Handlingar Svensk. Vet. Akad., xv, 1889, No. 6, p. 27. 



