98 PHILOSOPHICAL TRANSACTIONS. [ANNO 1797. 



till M. Lavoisier, in 1772, undertook a series of experiments for this purpose. He 

 exposed the diamond to the heat produced by a large lens, and was thus enabled to 

 burn it in close glass vessels. He observed that the air in which the inflammation 

 had taken place had become partly soluble in water, and precipitated from lime- 

 water a white powder which appeared to be chalk, being soluble in acids with effer- 

 vescence. As M. Lavoisier seems to have had little doubt that this precipitation 

 was occasioned by the production of fixed air, similar to that which is afforded by 

 calcareous substances, he might, as we know at present, have inferred that the dia- 

 mond contained charcoal ; but the relation between that substance and fixed air, 

 was then too imperfectly understood to justify this conclusion. •Though he ob- 

 served the resemblance of charcoal to the diamond, yet he thought that nothing 

 more could be reasonably deduced from their analogy, than that each of these sub- 

 stances belonged to the class of inflammable bodies. 



As the nature of the diamond is so extremely singular, it seemed deserving of 

 further examination ; and it will appear from the following experiments, that it con- 

 sists entirely of charcoal, differing from the usual state of that substance only by its 

 crystallized form. From the extreme hardness of the diamond, a stronger degree 

 of heat is required to inflame it, when exposed merely to air, than can easily be ap- 

 plied in close vessels, except by means of a strong burning lens ; but with nitre its 

 combustion may be effected in a moderate heat. To expose it to the action of 

 heated nitre free from extraneous matters, I procured a tube of gold, which by 

 having one end closed might serve the purpose of a retort, a glass tube being adapted 

 to the open end for collecting the air produced. To be certain that the gold vessel 

 was perfectly closed, and that it did not contain any unperceived impurities which 

 could occasion the production of fixed air, some nitre was heated in it till it had be- 

 come alkaline, and afterwards dissolved out by water ; but the solution was perfectly 

 free from fixed air, as it did not affect the transparency of lime-water. When the 

 diamond was destroyed in the gold vessel by nitre, the substance which remained 

 precipitated lime from lime-water, and with acids afforded nitrous and fixed air; and 

 it appeared solely to consist of nitre partly decomposed, and of aerated alkali. 



In order to estimate the quantity of fixed air which might be obtained from a 

 given weight of diamonds, 2-i- grs. of small diamonds were weighed with great ac- 

 curacy, and being put into the tube with J- oz. of nitre, were kept in a strong red 

 heat for about an hour and a half. The heat being gradually increased, the nitre 

 was in some degree rendered alkaline before the diamond began to be inflamed, by 

 which means almost all the fixed air was retained by the alkali of the nitre. The air 

 which came over was produced by the decomposition of the nitre, and contained so 

 little fixed air as to occasion only a very slight precipitation from lime-water. After 

 the tube had cooled, the alkaline matter contained in it was dissolved in water, and 

 the whole of the diamonds were found to have been destroyed. As an acid would 

 disengage nitrous air from this solution as well as the fixed air, the quantity of the 

 latter could not in that manner be accurately determined. To obviate this incon- 



