1<)04.] 



Oil Li([uid Hfjdroijen Calorirnftry. 



591 



and finally to the boilin,2: point of hydrogen. Early determinations 

 of the specific heat of carbon in any of its forms had shown complete 

 departure from the law of Dulong and Petit. In ] 872 Professor 

 H. F. Weber and myself,* working independently, fomidthat, as the 

 temperatm'c increased, the specific heat of carbon, whether as diamond 

 or as graphite, continued to increase. Professor Weber found that 

 *' the specific heat of the diamond is tripled when the temperature is 

 raised from 0^ to 200^" and my experiments showed that the mean 

 specific heat of carbon from oO° to the boiling point of zinc was 

 • ;J2, and to the temperature of the oxy-hydrogen blow-pipe (some 

 iiOOO°C.) it rose to 0*4:^, and I added "the true specific heat at 



Fig. 5. 



-zee c° £00° -^Y" tirn° ecc wco°c 



2000° must be at least 0*5; so that at this temperatm-e carbon 

 would agree with the law of Dulong and Petit." In 1875 f Professor 

 Weber published the results of further experiments, proceeding by 

 successive stages up to 1000° C, and showing " that from the point 

 (about 600°) at which the specific heat of carbon ceases to vary 

 with increase of temperature, and becomes comparable with that of 

 other elements, any real difference in the specific heats of the two 

 modifications disappears, and carbon obeys the law of Dulong and 

 Petit." 



Professor Weber plotted his results, taking specific heat as the 

 ordinate, to temperature as the abscissa, and producing a curve like 

 the old English /. He found the point of inflection for diamond 



* H. F. Weber, " The Specific Heat of Carbon," Phil. Mag. 1872, ser. 4, 

 ^;ol. xliv., p. 251. J. Dewar, " The Specific Heat of Carbon at High Tempera- 

 tures," I.e., p. 461. 



t Phil. Mag. 1875, ser. 4, vol. xlix., p. 285. 



