On the Rapid Production of Steam. 3J 5 



If the temperature assumed for comparison be precisely as much 

 above 212° as is equal to the number of degrees of heat, which be- 

 come latent in water while it passes into steam, it is evident that any 

 substance at comparable temperature, and possessing the same spe- 

 cific heat as water, would generate its own weight of steam in cool- 

 ing down to 212°. But if its own specific heat be less than that of 

 water, its weight must be proportionally increased, and then the 

 effect of cooling will be the production of the same weight of steam 

 as before supposed. Hence as the specific heat is directly propor- 

 tional to the quantity of steam which a given weight of metal would 

 produce, the latter may, at a known temperature, be assumed as a 

 measure of the former. By the following comparison it will be ev- 

 ident that the temperature adopted in these experiments was nearly 

 identical with that wdiich I have above alluded to, and which exceeds 

 2] 2°, by the amount of latent heat (990°) in a unit, by weight, of 

 steam. 



It must be observed that the above statements of specific heats, 

 taken from Petit and Dulong, are those of the mean effect from 0° 

 to 100° centigrade. That of silver, for example, is .0557 within 

 these limits, but if the mean specific heat found by them from 1° to 

 300° cent, be adopted it will come somewhat above the result of 

 my experiments, that is .0611. 



The method which has thus been adopted adds another to the 

 means heretofore employed for determining the specific heat of many 

 solid and gaseous substances, or at least of verifying the results of 

 former methods. The three modes, just alluded to, are those of 

 mixture, of melting ice, and of cooling in air, the last in particular 

 seems liable to many objections on account of the different conduct- 

 ing and radiating power of the bodies, and the different natures of 

 the surface which may be given to each,, whereby the time of cooling, 

 which is made the measure, will be exceedingly variable. 



The calorimeter, of Lavoisier, is not regarded as correct in its 

 indications, on account of the subsequent congelation of a portion 

 of the ice, melted by the hot body, and the rise of temperature in 



