the Elements Carbon, Boron, and Silicon. 163 



that they employed a method differing from that employed by 

 the latter physicist, and also that the substances examined could 

 not be considered perfectly identical. Had De la Rive and Mar- 

 cet examined more thoroughly into these differences, they must 

 easily have perceived the incorrectness of their mode of account- 

 ing for them (the method of cooling must give larger, not smaller 

 numbers than Regnault's method of mixtures ; small impurities, 

 trivial differences in the physical state of an element, may well 

 alter the specific heat of that element 1 per cent, or so, but surely 

 not 30 to 60 per cent.), and that remarkable property of carbon 

 the announcement and examination of which forms a part of the 

 following communication would thirty years ago have most pro- 

 bably been discovered. 



In his comprehensive research on the specific heat of solid 

 bodies*, Kopp estimated anew the specific heats of carbon, boron, 

 and silicon, using a modification of the method of mixtures ; his 

 results were as follows : — 



Gas-coke .... 0185 

 Furnace-coke . . 0*166 

 Native graphite 0*174 



Amorphous boron 0*254 

 Crystallizedboron 0*230 



Amorphous silicon 0*214 

 Fused silicon .... 01 38 

 Crystallized silicon 0*165 



These numbers are smaller than those of Kegnault. Kopp 

 explained the different numbers obtained by using different mo- 

 difications of carbon by supposing that carbon has in reality but 

 one specific heat (that of diamond, 0*1469), and that the other 

 varieties give higher numbers inasmuch as, being porous sub- 

 stances, they absorb gases, and on coming into contact with the 

 water of the calorimeter evolve a small quantity of heat. Kopp 

 believed that all the allotropic modifications of each element pos- 

 sess the same specific heat, and that variations in the number 

 actually obtained are due to the errors of experiment, or to the 

 use of impure materials. 



Several years later (1868) Wullner and Bettendorf attempted 

 to show that Kopp's hypothesis was untenable, that Regnault's 

 numbers were perfectly reliable, and that the smaller numbers 

 obtained by Kopp did not justify the conclusion which he had 

 drawn. The following are the numbers obtained by these 

 authorst : — 



Gas-coke 0*2040 



Native graphite . . . 0*1955 

 Furnace-graphite . . 0*1961 

 Diamond 0*1483 



These numbers agree very closely with Regnault's. Wullner 



* Liebig's Annalen, Ser. 3. Sup. vol. pp. i & 289. 

 t Fogg. Ann. vol. cxxxiii. p. 293. 

 M2 



