Graphite . 0*1883 

 Diamond . 0-1429 



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



and Bettendorf concluded that the different modifications of 

 carbon have really different specific heats. In obtaining these 

 numbers a small error was introduced by the following circum- 

 stance. The substance to be examined (1 to 5 grms.) was 

 warmed in a glass with water to about 70°, and then allowed to 

 cool to about 20° in the calorimeter. In calculating the specific 

 heat of the substance, it was assumed that the specific heat of the 

 water remained equal to unity throughout the experiment. Now 

 the average specific heat of water between 20° and 70°, according 

 to Bosscha*, is 1 *0099. Taking this number into account, Wiill- 

 ner and Bettendorf 's numbers become : — 



Gas-coke . . . 0*1961 

 Furnace-graphite. 0*1861 



If we use the number for the specific heat of water between 

 20° and 70°, obtained by Jamin and Amauryf, these numbers 

 become still smaller. We may say, then, that the numbers ob- 

 tained by Wiillner and Bettendorf stand midway between those 

 of Kopp and those of Regnault. 



From a consideration of the results of all the researches upon 

 the specific heats of carbon, boron, and silicon, it may safely be 

 averred that the different allotropic modifications of these ele- 

 ments possess different specific heats, and that no one of these 

 elements in any of its modifications obeys the law of Dulong and 

 Petit. These three solid elementary bodies differ in this respect, 

 therefore, from all the other elements. It is also, however, evi- 

 dent that the numbers obtained by the different experimenters 

 diverge considerably from one another. The four series of de- 

 terminations have not presented us with any two exactly similar 

 numbers. The differences in the individual results are so great 

 and so general as to preclude us from believing that they are due 

 to errors in the methods of experiment, or to impurities in the 

 substances themselves. Some circumstance really conditioning 

 the specific heat of these elements, and the value of which differs 

 in the four series of experiments, must be present. 



With this idea I undertook, in the winter of 1871-72, an 

 analysis of the estimations hitherto made of the specific heats of 

 carbon, boron, and silicon, and arrived at the following conclu- 

 sion : — The different observers have determined the specific heats 

 of these elements for entirely different intervals of temperature ; and 

 the greater the interval of temperature for which the specific heat 

 is determined, the greater is the number representing that specific 

 heat. The following Tabic shows that this is the case. Column C 



* Pogg. Ann. Jubeibd. p. 545. 

 f Comptes Rendus, vol. lxx. p. 



p. 661. 



