On Gems, 197 



is electric when rubbed, and aflects the electrometer iviik 

 ihc negative Jioiccr. 



It was always supposed to be the most refractory and in- 

 destructible in the fire, till the experiments of d'Arcet and 

 AJacquer proved the contrary : but thev supposed it to be 

 volatilized ; they had no idea of its combustion. D'Arcet 

 and Macquer's experiments were made in consequence of 

 an observation of Boyle's, that the diamond, when exposed 

 to the action of a violent fire, emitted acrid vapours. 



The emperor Francis the First caused diamonds and ru- 

 bies to be exposed in crucibles to a reverberatory fire for 

 24 hours : the diamonds disappeared, but the rubies re- 

 mained unaltered. These experiments he had again repeated 

 at an expense of six thousand florins. 



The grand duke of Tuscanv had a series of experiments 

 inade with a large mirror and the concentrated rays from 

 the sun upon the diamond, in which it was destroyed. It 

 required a short period for its being completely volatilized, 

 as it was then called. 



Macqner seems latterly to have had another opinion, when 

 he says, he observed the diamond dilated and swelled up, 

 and that a blue flame was observable on its surface. 



Lavoisier and Cadet proved the combustion of the dia- 

 mond, and that it ceased as soon as the oxygen was de- 

 stroyed ; and that the stone only burnt in proportion to 

 the oxygen present, like all other combustible substances. 

 Lavoisier also observed that the gas produced during the 

 combustion precipitated lime water, which eft'ervesced upon 

 the addition 6f an acid. 



Sir Isaac Newton, from its great power of refracting the 

 light, conjectured it was a combustible body : his words 

 are, '^ it is probably an unctuous body coagulated." 



Tennant exposed two grains and a half of small diamonds 

 and a quarter of an ounce of nitre (nitrate of potash) in a 

 gold tube, connected with a pneumatic apparatus, in a red 

 heat for an hour and a half: the gas that \\ as given out was 

 from the decomposition of the nitre, with scarcely a trace of 

 carbonic acid ; but the residuum, upon careful examination, 

 had been partly converted intp carbonate of p(;tash ; thr^ 

 diamonds had completely disappeared. Upon analysino- the 

 residuum, as umch carbonic acid gas was obtained as would 

 occupy the space of 10*1 ounces of water. Upon repeatint', 

 this experiment with another weight of diamonds, lie foun?. 

 the proportions as 10-3 of carbonic acid to two grains and 

 a halt of diamond : two cfraiu'^ and a Ijalf of charcoal woidd 

 have uiven ten of curbomc acid. 



N 3 That 



