434 W. G. Mixter — Carbon and its Heat of Combustion. 



Art. XLYI. — A New Allotrope of Carbon and its Heat of 

 Combustion ; by W. G. Mixter. 



[Contributions from the Sheffield Laboratory of Yale University.] 



The investigation of the carbon which separates when acety- 

 lene nnder pressure is exploded forms a part of the study of 

 the thermal constants of the gas. The heat of formation of 

 acetylene according to Thomsen is 47,700 calories ; Berthelot's 

 figures are 51,400 calories, and the writer by a direct determi- 

 nation obtained 53,300 calories for the heat of dissociation.* 

 As these results vary so much it appeared desirable to investi- 

 gate the thermal constants of the constituents of acetylene. 

 The work on hydrogen has been published. r The writer con- 

 cluded from the study of acetylene that the carbon from it 

 would give a different heat of combustion from that of other 

 forms of carbon. The results obtained confirm this view and 

 indicate that acetylene carbon is a distinct allotropic form. 

 The thermal effect of burning 12 grams of different kinds of 

 carbon found by Favre and Silbermann, Berthelot, and the 

 writer is as follows : 



Gas 

 Wood Sugar retort 



charcoal, charcoal, carbon. Graphite. Diamond. 



96,960 c 96,500 c 96,568° 93,559 c 93,240 c Favre & Silbermann 

 97,650° 94,810 c 94,310° Berthelot 



9&,700° 94,000 c M. 



Acetylene carbon 94,728° 



The figures show that the carbon from acetylene is very dif- 

 ferent from the amorphous varieties of the charcoal type, and 

 that its heat of combustion is nearly the same as that of 

 graphite. Moissan has shown that it is not graphite, and does 

 not contain graphite, as it does not yield graphitic acid on 

 treatment with a mixture of potassium chlorate and fuming 

 nitric acid, and my own test gave the same conclusive result. 



The acetylene carbon as it comes from the bomb is a greyish 

 black, lusterless and very bulky, porous mass. When com- 

 pressed it has a brilliant black luster, but not the metallic 

 appearance of graphite. It is a good conductor of heat and 

 electricity. While one gram condenses one milligram of dry 

 air on its surface and in the pores, it does not exert catalytic 

 action on the gases of decay in presence of air, such as we are 

 familiar with in case of charcoal. When a mixture of acety- 

 lene carbon and sulphuric acid is boiled no odor of sulphur 

 dioxide is perceptible, but the escaping vapors turn a blue 



* This Journal, xii, 347. f This Journal, xvi, 214. 



