268 Methods of determining and calculating 



fessor Meyer on the woods and by Prof. Leslie and Mr. Dalton on 

 other bodies. 



The fourth method employs the heat which becomes latent when 

 water is rapidly converted into vapor at its boiling point, by the di- 

 rect and sole agency of the solid, heated to a known temperature 

 above that point. This method may be successfully employed to 

 determine the latent heat of melting metals as well as their specific 

 heat from 212° to their melting points, and also their change of ca- 

 pacity, if any, after they have passed into the hquid state. The 

 weight of boiling water which they will under different circumstances 

 convert into vapor, compared with the effect of the same amount of 

 water, conceived to be heated to the same temperature as the solid, 

 gives again the numerical expression of the specific heat. 



It is evident, that if this fourth method be adequate to give the 

 specific heat when the temperature is known, it is also competent to 

 give the temperature when the specific heat is known ; but in order 

 to remove all doubt as to its applicability to the latter purpose, it is 

 well to ascertain by different and independent methods the exact in- 

 dex of the specific heat, whether uniform or variable, of the solids 

 which may be employed for this purpose. Among the substances 

 adapted to this end, are pure malleable iron and pure platlna. They 

 are both highly indestructible, Avhen heated without the access of 

 foreign ingredients, such as oxygen, sulphur, carbon, silica, &z;c., and 

 though the specific heat of the former is represented by some writers 

 as increasing pretty rapidly, with the temperature, yet this increase 

 is not by any means in so great a ratio, as that of its dilatations, 

 which other authors have proposed to employ as standards for meas- 

 uring very high temperatures. As to platina, its specific heat is 

 low, and its increments of rate, both in dilatation and specific heat, 

 are represented as very moderate. I may here remark that the ex- 

 periments of Dulong and Petit on this subject appear to have been 

 erroneously stated in one part of their prize memoir, which has 

 doubtless led to the supposition that they discovered no increment 

 of capacity in platina by tlie elevation of temperature. In their ta- 

 ble of the specific heats of the different metals at 100° and at 300° 

 Centigrade, as originally published in the Annales de Chimie, Vol. 

 VII, we find .0355 placed under both of those temperatures against 

 platina. The same numbers are transferred into every English edi- 

 tion of works in which I have seen that table, with the single excep- 

 tion of Turner's Chemistry, in which the number is .0335 both for 



