W^ Br. H. F. Weber on the Specific Heat of Carbon, 



of this apparently small variation is that the values found for 

 gas-coal and graphite must be diminished by 1^ or 2 per cent.^i^ 

 The amount of this correction for the diamond cannot be calcu- 

 lated from the data given in the memoir mentioned, because 

 they appear to be vitiated by numerous misprints ; most pro- 

 bably, however, it is of the same order as the above ; and con- 

 sequently the very good accordance mentioned between the values 

 found by MM. Wiillner and Bettendorf and by M. Regnault 

 vanishes. 



In order to aftord a readier view, the results of the four series 

 of experiments just mentioned are placed together in the follow- 



ing Table :— 



- 













Observers. 



Wood 

 charcoal. 



Gas-coal. 



Native 



graphite. 



Furnace 

 graphite. 



Diamond. 



Temperature- 

 interval. 



Regnault 



02415 

 -2009 



0-2036 



0-185 



0-2006 



0-2019 



0174 

 0-1919 



01970 



0165 

 01921 



01469 

 0-1146 



0-1452 



8° to 98° 



3° to 14° 



22^ to 52= 



22'' to 70° 



De la Rive and! 



Marcet J 



Kopp 



Wullner and! 

 Bettendorf... J 



The preceding Table shows that all four series of experiments 

 agree in this — that carbon in its various allotropic modifications 

 possesses quite different specific heats, and that none of them can 

 fulfil the law of Dulong and Petit; but it shows also that the 

 values found by the different observers for the same modification 

 differ widely from one another. The divergences are so great 

 and universal that they cannot be accounted for through the dif- 

 ferent methods of observation, nor through impurity of the sub- 

 stances. Since, how^ever, in the four series of experiments the 

 temperature-intervals were each different from the others (as 

 the last column of the Table shows), and since for each of the 

 above modifications the values found rise and fall in a perfectly 

 regular manner with the upper limit of the temperature-interval, 

 it appeared to me in the highest degree probable that the cause of 

 the total noncoincidence of the results hitherto attained might 

 be, that the specific heat of carbon in all its allotropic modifi- 

 cations varies to a considerable degree with the temperature. 



A closer investigation has completely verified this conjecture. 

 The specific heat of carbon increases with the temperature, and 

 more considerably than that of any other substance ; the specific 

 heat of the diamond is tripled when the temperature is raised from 

 0° to 200° ! 



* About 15 per cent, if the value r052j found by Jamin and Amaury 

 (1871) for the mean specific heat of water between 20° and 70^ be taken 

 as the basis of the calculation. 



