104 Cemhttjlion of the Diamond. 



experiments detailed in the Journal de Phyfique, this efFe£l was not uniformly produced, 

 and has not been properly explained. I did not obferve any of thefe appearances on dia- 

 monds which had been expofed to various degrees of heat between 15° and 30°. There 

 was a fort of luminous haze round the diamond while burning, but fo feeble as to be 

 fcarcely perceptible *. 



During the combuftion of a diamond, I placed befide it a fmall piece of plumbago, and 

 obferved, that the latter exhibited a luminous appearance fimilar to that of the former, but 

 h began at a lower temperature. The air being excluded for a few minutes by clofing the 

 mouth of the muffle, the diamond and plumbago both loft their brightnefs ; but this foon 

 returned, after the air was allowed to circulate in the muffle, and was much increafed by 

 blowing on them with a pair of bellows. 



I expofed a diamond fixed in a fine platina wire to the aftion of the blow pipe, during 

 which treatment its confumption was extremely flow, ov/ing, I prefume, to the impurity 

 of the air blown upon it. 



In order to afcertain at what temperature this fubftance begins to be confumed, I placed 

 a diamond with a pyrometer on a piece of baked clay, and pufhed them gradually into the 

 muffle. As foon as both were perfedly red throughout, the pyrometer was withdrawn, 

 and indicated 13°. The diamond had acquired the dim milky appearance already men- 

 tioned. The diamond and pyrometer were replaced in the muffle, and the heat being 

 flowly increafed, till the glow appeared, was continued as equal as pofllble, till the dia- 

 mond was totally confumed: the pyrometer was then meafured, and indicated 14° f. In 

 another diamond, the heat requiCte to produce the glow was 15°, and at this temperature 

 it was wholly confumed. 



Thefe obfervations were made in prefence of Lord Webb Seyniour, Sir James Hall, 

 and Dr. Kennedy. 



The experiments above-mentioned were feveral times repeated with different diamonds : 

 and the refult of the two laft fhows, that the heat required for their combuftion is far 

 below what has hitherto been fuppofed neceffary. 



The experiment of Guyton, in vvhich the diamond was totally converted into carbonic 

 acid by its combuftion in oxygene gas, has afforded a decifive proof of its identity with 

 carbon. This important difcovery has been farther confirmed by obtaining fteel from the 

 union of diamond with foft iron. I repeated the latter experiment in the following 

 manner. 



• " On a apper;u a leur fiirface, deja diminuce de volume, tine flamme legere, et entierement Temblable, 

 pour la couleur, a celle que Ton voit onduler fur une portion dePhofphore expose a I'air libre." Jonrn. de 

 Ph. Vol. II. for 1771, p. 114. 



+ The pyrometers ufed in thele experiments were made fome years ago by the late Mr. Wedgwood ; 

 and are the fame with thofe which he has defcribed in Vol. 76 of ths Philofophical Tranfaftions of London. 

 I mention this becaufe thofc lately fold at the raanufailory, do not agree with the former ftandard. 



Into 



