1898.] on Experiments on Certain Elements in relation to Heat. 739 



The " Law " of Dulong and Petit is therefore only an approxima- 

 tion ; but this may perhaps be due to inaccuracy in the estimation of 

 the specific heat, owing'to impurity in the material used. That is the 

 problem which I have endeavoured to solve. 



The introduction by Professor J. Joly of a new method of calori- 

 metry, which depends upon the condensation of steam upon the cold 

 body, and the excellent results obtained by the Author in the use of 

 the differential form of his instrument,* led me to think that with 

 due attention to various precautions — such as exact observations of the 

 temperatures, and practice in determining the moment at which the 

 increase of weight due to condensation is completed — results of con- 

 siderable accuracy might be obtained. 



The problem is to find two elements, very closely similar in 

 density and melting point, which can be obtained in a state of purity, 

 and then to determine with the utmost possible accuracy the specific 

 heat of each under the same conditions. 



The two metals cobalt and nickel were selected for the purpose. 

 They were examined by Reguault, but the metals he used were very 

 impure. 



The cobalt employed in my experiments was prepared by myself. 

 For the nickel I am indebted to Dr. Ludwig Mond. Both were 

 undoubtedly much more nearly pure than any metal available in 

 Eegnault's time. The results obtained are as follows : — 



Specific Heats of Cobalt and Nickel 

 Pure fused. 



Cobalt, S.G.^, 8-718. 



4c 



■10310 

 10878 

 10310 

 -10355 

 10373 

 10362 



Aritli. mean 



10348 



2r 



Nickel, S. a ^8-790. 



•10953 



•10910 \ toohi^h? 



•10930 



10931 



The value arrived at for cobalt is much lower than that ( • 1067) 

 derived from Regnault's experiments, while that for nickel is practi- 

 cally identical with Kegnault's, which is * 1092. This is certainly 

 too high. 



Further experiments will be made. Already, however, I feel 

 certain that Kopp's conclusion is right, and that the law of Dulong 

 and Petit, even for the metals, is an approximation only, and 



* Proc. R. S. 47, 241, 



