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



(1) Reasoning from analogy, it may be supposed that the dif- 

 ferent modifications of boron and silicon will show, as regards 

 specific heat, a behaviour similar to that of the modifications of 

 carbon. This point I hope to settle by experiments carried out 

 during the present winter. 



(2) It may be supposed that the specific heats of those com- 

 pounds into the composition of which carbon, silicon, or boron 

 enters, will exhibit a variation with the temperature analogous 

 to that exhibited by the elements themselves. My experiments, 

 so far as they have gone, fully bear out the truth of this sup- 

 position. 



The physical cause of the variation in the specific heat of car- 

 bon is to be sought for in the constitution of the atoms, not in 

 that of -the molecules. 



On the supposition that the specific heats of the elements 

 hydrogen and oxygen are as constant in their compounds as in 

 the free state (and there seems no reason to doubt the truth of 

 this supposition), it is possible, from a series of observations at 

 different temperatures of the specific heat of a compound (C, H), 

 (C, 0), or (C, 0, H), to deduce the specific heat of the carbon 

 in the compound as a function of the temperature. 



So far as my researches have gone, I find that, in gaseous and 

 liquid carbon compounds, the specific heat of the carbon is a 

 function of the temperature, but that the nature of this function 

 varies from compound to compound. The specific heat of carbon 

 when in combination is a function of the temperature and of all 

 those circumstances which influence the quality of the non-carbo- 

 nated part of the compound molecule. Thus the specific heat of 

 carbon in carbon monoxide, CO, for every degree of temperature 

 from —30° to 250°, is totally different from the specific heat of 

 carbon in the dioxide, C0 2 ; the function of the temperature 

 representing the specific heat of carbon in the compound CH 4 is 

 of an entirely different nature from that representing the specific 

 heat of the same element in the compound C 10 H 16 .. 



Hence it follows that the constitution of the carbon atom 

 differs according to the nature of the molecule of which it forms 

 a part ; for example, the carbon in C0 2 is of a different nature 

 from the carbon in CO. Hence it is self-evident that the 

 " chemical value " of carbon is not constant; that "varying 

 equivalency " or " polyequivalency " of carbon is possible, as is 

 indeed exhibited in the compounds CO and C0 2 . 



In the specific heat of carbon, considered as a function of the 

 temperature, we have 'therefore a means of settling one of the 

 most important questions in the theory of the carbon compounds 

 — the question as to the constancy or variability of the nature of 

 the carbon atom in the compounds formed by that element. A 



