NATt RE OF THE. DIAMOND. 151 



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

 which remained precipitated lime from lime-wat^r, and with acids 

 afforded nitrous nnd 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^ grs. of small ilia- 

 inonds were weighed with great accuracy, and being put into the 

 tube with 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 iiilhtiu'd, by which moans almost all the fixed air was re. 

 tained 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 inconvenience, the fixed air was made to unite with 

 calcareous earth, by pouring into the alkaline solution a sufficient 

 quantity of a saturated solution of marble in marine acid. The 

 vessel which contained them being closed, was left undisturbed till 

 the precipitate had fallen to the bottom, the solution having been 

 previously heated that it might subside more perfectly. The clear 

 liquor being found, by means of lime-water, to be quite free from 

 fixed air, was carefully poured oil' from the calcareous precipitate*. 

 The vessel used on this occasion was a glass globe, having a tube 

 annexed to it, that the quantity of the fixed air might b more 

 accurately measured. After as much quicksilver had been poured 

 into the glass globe containing calcareous precipitate as was neces. 

 nary to fill it, it was inverted in a vessel of the same fluid. Some 

 marine acid being then made to pass up into it, the fixed air was 

 expelled from the calcareous earth ; and in this experiment, in 

 which 2{ grs. of diamonds had been employed, occupied the space 



* If much water had remained, a considerable portion of the fixed air 

 would have beeo absorbed by it. But by the bom* method as that described 

 above, I observed, that as much fixed air might be obtained from a solution 

 of mineral alkali, as by adding an acid to an equal quantity of the ume kind 

 of alkali. ORIC. 



fc4 



