the Elements Carbon, Boron, and Silicon. 285 



The differences of the two consecutive numbers in these series 

 are 



For graphite. For diamond. 



76-68 .... 76-39 

 100-23 .... 9945 



As the differences for graphite are J*! *f jj I greater than those 



for diamond, these new 'experiments show that the specific heat 

 of graphite is a very little greater than that of diamond, viz. 



00020 between 550 and 750, 

 00031 „ 750 „ 1000. 



This agrees with the previously obtained results. 

 (3) The results 



Graphite. Diamond. 



y w6 . 7 =0-4431, 0-4408, 



y 806 . 5 =0-4539, 0-4489, 



2, 985 . =0-4674, 0-4589, 



show 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 o/*Dulong and Petit. 



By multiplying the values obtained for the specific heat of 

 carbon between 600° and 1000° by the generally received atomic 

 weight 12 (deduced from the vapour-density of carbon com- 

 pounds), we obtain a product varying from 5*4 to 5*6, which 

 agrees with the atomic heat of those other elements which have 

 small atomic weights (aluminium 5*7, phosphorus 5 '5, sulphur 

 5-5, &c). 



All the anomalies in the specific heat of carbon disappear when 

 the temperature reaches a red heat. 



The results which I have obtained are not in keeping with 

 those of Dewar*, who obtained for gas-carbon the number 0-314 

 as representing the mean specific heat from 20° to 1040°, for 

 graphite 0*310, and for diamond 0-366. For the mean specific 

 heat of " carbon " between 20° and the temperature of the oxy- 

 hydrogen blowpipe (estimated at 2100°) Dewar obtained the num- 

 ber 0-374. 



From these numbers Dewar concludes that " the true specific 



* British Association Reports, 1872, aud Phil. Mag. December 1872. 



