286 Dr. H. F. Weber on the Specific Heat of 



Jieat of carbon at 2000° must be at least 0*5 ; so that at this tem- 

 perature carbon would agree with the law of Dulong and Petite 



r»i046;4 



By comparing the mean values I ydT=z 0*3879 for graphite, 



' J22-6 

 /*1051*2 . » . » . . 



and I ycffl= 0*3776 for diamond, obtained by me with 



DewarY numbers, considerable differences are disclosed. All 

 my experiments show that the mean value of the specific heat of 

 graphite is somewhat greater than that of diamond: the direct 

 results detailed on p. 284 establish the truth of this statement. 

 Some cause of error has probably crept into Dewar's experiments ; 

 one of these causes may be the omitting to measure the exact 

 temperature of the carbon when it was thrown into the Calori- 

 meter, this temperature being taken as equal to that of molten 

 zinc. The temperature of the carbon must, however, have been 

 rather less than 1040°, inasmuch as the heating-vessel was fur- 

 nished on its outer rim with an iron disk (to shield it from zinc 

 oxide) ; and as this disk was much cooler than the vessel itself, 

 heat must have been lost in carrying the apparatus to the calori- 

 meter. Whether this error was large enough to lower the spe- 

 cific heat of carbon between 20° and 1000° from 0-388 to 0'310, 

 or whether there were other errors also present, I cannot under- 

 take to say. I am inclined to place a greater degree of confi- 

 dence in my own experiments, inasmuch as the temperature of 

 the substance at the moment when it fell into the calorimeter 

 was determined with the greatest accuracy. The expectation 

 that, " starting from absolute zero, carbon or graphite most pro* 

 .bably increases regularly in specific heat, whereas .diamond 

 probably diminishes until we reach — 42°'3 C, and then in- 

 creases regularly until it exceeds that of graphite, which it con- 

 tinues to do until they agree at very high temperatures," has 

 been fully realized in the case of graphite only : the variations 

 in the specific heat of diamond are much simpler than Dewar 

 supposed. 



C. The Specific Heat of dense amorphous Carbon. 



The following Tables show the results of experiments upon a 

 sample of dense carbon contained in the limestone of Wundsiedel 

 in the Fichtelgebirge : this carbon was but little less dense than 

 lamellar graphite; it left but 0*33 percent, of ash. 



