390 Royal Society : — 



Mr. Joule had proved the theorem, but only that he had offered 

 it ^s an opinion, I do not see why this opinion should have the 

 priority over that which Holtzraann had arrived at three years 

 before. 



In conclusion allow me to make one remark. In a more recent 

 paper, " On a Modified Form of the Second principal Theorem in 

 the Mechanical Theory of Heat*," I have introduced, instead of 

 Carnot's function C, another function of the temperature, which 

 I have designated by T, and by which all developments are very 

 much simplified. This function has a determinate relation to 

 that of Carnot's, which I have expressed by the equation 



dT 



dt _A 



T ~C' 

 in which / represents the temperature, and A the equivalent of 

 heat for unit of work. It is easily recognized, that, according to 

 this equation, the functions C and T are in general to be con- 

 sidered different; but that for the special case, in which C is 

 proportional to the absolute temperature, T must be also pro- 

 portional to it. And in fact I have shown, from the same prin- 

 ciples which before led me to the determination of C, that in all 

 probability T is simply the absolute temperature itself. 

 I remain. Gentlemen, 



With great respect, yours &c., 

 Zurich, March 20, 1856. R- Clausius. 



L. Proceedings of Learned Societies. 



ROYAL SOCIETY. 

 [Continued from p. 306.] 

 December 6, 1855. — Sir Benjamin Brodie, Bart., V.P., in the Chair. 



1"^HE following communication was read : — 

 " On Chemical Affinity, and the Solubility of the Sulphate 

 of Baryta in Acid Liquors." By F. Crace Calvert, Esq. 



Sohbility of the Sulphate of Baryta. 

 The author observes that sulphate of baryta is not an insoluble 

 salt, as is generally admitted, for he has found that 1000 grs. of nitric 

 acid, of spec, grav, ri67, are capable of dissolving 2 grs. of sulphate 

 of baryta ; and what renders the knowledge of this fact still more 

 useful in analytical chemistry is, that the insolubility of this salt is 

 affected even by the weakest nitric or hydrochloric acids ; for whilst 

 0*062 gr. of sulphate of baryta only requires 1000 grs. of nitric acid, 

 of spec. grav. 1'03'2, to hold it in solution, the same quantity of salt 

 requires 50'000 grs. of pure distilled water to dissolve it. 

 * Poggendorflf's Annalen, vol. ,\ciii. 



