DIAMOND. 



the jewellers who expose diamonds which 

 are foul to a strong heat, imbedded in 

 charcoal, to make them clear. An ob- 

 servation of Macquer first threw light 

 on this subject. He took notice, that 

 while the diamond was exposed to a 

 strong heat under a muffle, and while 

 it was losing weight, it was luminous, 

 and appeared to burn, a fact which he 

 verified by subsequent experiments. It 

 cannot be doubted, therefore, that in 

 the experiments of Darcet air had been 

 admitted to the diamonds, from rents in 

 the porcelain clay balls in which they 

 were inclosed, and that in the method 

 of jewellers they are more effectually 

 protected from the action of the air, by 

 the charcoal dust with which they are 

 surrounded. 



Still a degree of uncertainty was at- 

 tached to the subject, and to remove 

 this, Lavoisier, associating with him in 

 the investigation Macquer and Cadet, 

 undertook some experiments. They first 

 ascertained, that in close vessels the dia- 

 mond does not evaporate : having expos- 

 ed 19* grams in a luted earthen retort, 

 connected with a glass receiver, and the 

 jointing secured, to a very strong heat, 

 the loss ot weight amounted only to about 

 two grams ; yet the heat applied was 

 much higher and continued much longer, 

 than would have been necessary to dissi- 

 pate the entire quantity of diamond in the 

 open air -, and repeating the experiment 

 of the jewellers, they found, that when 

 carefully imbedded in charcoal powder, 

 from w'hich the air was excluded, the 

 most violent heat produced no change in 

 the diamonds submitted to trial. They 

 were therefore disposed to conclude,that 

 the dissipation of the diamond, when heat- 

 ed in the open air, was owing to its com- 

 bustion. (Memoirs de i'Acad. des Sci- 

 ences, 1772, p. 350.) Facts similar to 

 these were established by asecond series 

 of experiments performed by Darcet and 

 Rouelle. And Lavoisier, in another me- 

 moir, demonstrated more decisively the 

 combustibility of the diamond, and dis- 

 covered the product of its combustion. 

 When suddenly heated by a lens,he found 

 it to decrepitate, and to be thrown into 

 small fragments; when heated more 

 slowly il was dissipated without this de- 

 crep tation. When heated by a lens, in a 

 glass vessel placed over water, it was still 

 dissipated, and in the first experiment no 

 sensible product was obtained) in a se- 

 cond he observed,thatwhen the heat was 

 less powerful, the surface of the diamond 

 became black, and was sensibly covered 



with a thin coating of charcoal. In a sub- 

 sequent experiment, he found that the 

 air of the vessel in which the experiment 

 was made was diminished in volume to 

 the extent of about eight cubic inches in 

 60 ; on pouring into this residual air 

 lime water it became milky, as it would 

 have done from exposure to air in which 

 charcoal had been burnt ; and by sub- 

 jecting it to different trials, thismilkiness 

 was found to be owing to the presence of 

 carbonic acid, which of course had been 

 produced during the combustion of the 

 diamond. The same results were obtain- 

 ed on heating the diamond in a glass ves- 

 sel containing common air, placed over 

 quicksilver. Lavoisier drew the conclu- 

 sion, that the diamond is a combustible 

 body ; and that, as objects of chemistry, 

 there exists a great analogy between 

 it and charcoal. 



Some years afterwards Guyton shewed 

 that the diamond is consumed whenheat- 

 ed with the nitrate of potassa, and affords 

 carbonic acid. This experiment was re- 

 peated with more precision by Mr. Te- 

 nant. He exposed to a strong red heat, 

 for an hour and a half, in a gold tube,two 

 grains and a half of small diamonds with a 

 quarter of an ounce of nitrate of potassa. 

 The salt was decomposed,and,on examin- 

 ing the residuum,the potassa was found to 

 have attracted carbonic acid, while the 

 diamonds were entirely consumed. The 

 quantity of carbonic acid was attempted 

 to be ascertained, by adding to the solu- 

 tion of the residuum in water a solution 

 of muriate of lime: a precipitate of carbo- 

 nate of lime was formed; from this the 

 carbonic acid was disengaged by muriatic 

 acid, and it occupied a space equal to 

 about 10.1 ounce measures of water. 

 This, according to Mr. Tennant's calcu- 

 lation, was about the quantity that ought 

 to have been obtained from two grains 

 and a half of charcoal combined with oxy- 

 gen; and he therefore concluded that the 

 diamond is charcoal, and differs from that 

 substance only in its crystallized form. 



Guyton at length investigated the sub- 

 ject with that precision, which was ne- 

 cessary to fix our opinion as to the na- 

 ture of the diamond. The diamond, an 

 imperfect octahedron, was placed on a 

 small porcelain crucible, elevated in a 

 jar filled with oxygen gas, ascertained 

 to be pure, placed over mercury. The " 

 concentrated solar rays were thrown on 

 the diamond by a large lens : it appear- 

 ed at first farinaceous, and was after- 

 wards sensibly blackened on its surface : 

 the appearance of combustion was ex- 



