THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. X. — On the Mechanical Equivalent of the Heat 

 Valorization of Water ; by R. H. Hough. 



The object of this investigation is the development of a 

 method for the determination of the mechanical equivalent of 

 the heat of vaporization of water directly in ergs : i. e., of a 

 method not involving the use of the calorie. 



This equivalent, which will be designated in what follows 

 by L, is usually expressed in terms of the calorie varying from 

 536 C. to 540 C, depending on the particular calorie taken as 

 the unit and the particular method pursued. 



Regnault's is the only classic determination. He defined 

 the calorie as the amount of heat to raise a kilogram of water 

 from 0° to 1°, and worked out the following formula : 



L=606'5 — 0-695*— 0-00002* 8 — 0*0000003« s 



At standard pressure this gives the value 536*5, which is 

 generally used by physicists, notably by Joly in the reduction 

 of his determinations with the steam calorimeter. In close 

 agreement with this value is the 536*2 of Berthelot, whose 

 method was much less complicated. The empirical formula of 

 Griffith :* 



L = 596'73 — 0-60U 



gives the value 536'63 in terms of the calorie from 14°*5 to 

 15°*5 centigrade. This agreement is only apparent, and a 

 more just value of L is obtained by following Callendar,f who 

 estimated L from the observations of Joly and Barnes. Joly:): 



* Griffith, Phil. Trans. A., 1895, p. 261. 

 t Callendar, Proc. Roy. Soc, lxvii, 1900. 

 % Joly, Proc. Roy. Soc, xlvii, 1889. 



Am. Jour. Sci.— Fourth Series, Yol. XX, JS r o. 116.— August, 1905. 

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