Chap. 44,} Experiments on Di&mcnds. 285 



flammable fubftances; and it was therefore neceiTary 

 to fuppofe, that the porcelain earth, in which the other 

 diamonds were inclofed, fuffered fome fmall ieparation 

 from expofure to heat, which, though fo minute as 

 to efcape obfervation after the ball was cold> was yet 

 fufficient to admit the air. This opinion was fully 

 confirmed by the experiments of M. Lavoifier, who 

 found, that diamonds are only confumed in proportion 

 to the quantity of vital air to which they are expofed. 

 He alfo found, that the .combuftion of the diamond ' 

 was attended with the formation of carbonic acid gas ; 

 but at the time he made his experiments, the nature 

 of that fluid does not feem to have been diffidently 

 \inderilood, to enable this great philofopher to draw 

 a correct conclufion relative to the compofition cf the 

 diamond. 



The experiments of Lavoifier were purfued by Mr. 

 Tennant, and their relult may be found in the rirft 

 part of, the Philosophical Tranfaclions for the year 

 1797. He obferved that, from the extreme hardnefs 

 of the diamond, a flronger heat was required to in- 

 flame it, when expofed merely to air, than could eafily 

 be fupplied in clofe veiTels, except by means of a ftrong ' 

 burning giafs ; but that with nitre * its combuftion 

 could be effected in a moderate heat. To expofe it 

 to this procefs, without any danger from the intrufion 

 of extraneous matters, Mr. Tenna'nt inclofed the nitre 

 and the diamond in a tube of gold, and took every 

 neceffary precaution to prove that no carbonic acid gas, 

 or fixed air, could be included, except what the diamond 

 itfelf afforded. When the diamond was entirelydeftroyed 

 in the gold vefiel by the inflammation of the nitre, the 

 fubftance which remained precipitated lime from lime 



* The ufe of the nitre is obvioufiy to fupply a quantity of pure 

 air to effeft the comhullion. 



water, 



