DIAMOND. 



tremely faint, and when it had begun, 

 did not continue if the solar heat was 

 withdrawn. Afterwards, when a more 

 powerful lens was employed, the com- 

 bustion was more evident ; the diamond 

 first became black, and of a coally ap- 

 pearance ; an instant after it became 

 brilliant, and at some points appeared 

 to boil ; it gradually diminished, and the 

 application of the solar heat was repeat- 

 ed at different times until it was entirely 

 consumed. The quantity of carbonic 

 acid which had been formed was ascer- 

 tained by introducing' a solution of ba- 

 rytes in water, and the unexpected re- 

 sult obtained, that the quantity was 

 much greater than what would have been 

 formed by the combustion of the same 

 weight of charcoal as of diamond. Twen- 

 ty -eight parts of charcoal in burning com- 

 bine with 72 of oxygen, and from 100 of 

 carbonic acid ; while the same weight of 

 acid, according to Guyton's experiment, 

 is formed from the combustion of 17.88 

 of diamond, which combine therefore with 

 82.12 of oxygen. Guyton concluded, 

 therefore, that it is not merely by its co- 

 lour, weight, hardness, transparency, and 

 other sensible qualities, that the diamond 

 differs from charcoal ; neither does the 

 difference depend on the state of aggre- 

 gation, nor are the distinctive properties 

 of charcoal owing to the two hundreth 

 part' of residue which it leaves in the form 

 of ashes, or to the small quantity of hy- 

 drogen which it may contain ; but to its 

 oxydation, diamond being the simple base 

 of which charcoal is the oxide. 



A striking fact, with regard to the oxy- 

 g enizement of the diamond, is the high 

 temperature which is requisite to its 

 taking place. It appears, from Guyton's 

 statement, to be charred at about the 

 temperature of 18 or 20 of Wedgwood's 

 scale, (3417 or 3677 of Fahrenheit's) 

 and at about 30 (4977) it burns with a 

 feeble flame ; nor does it even in oxy- 

 gen gas produce as much heat as to 

 support its own combustion. This is no 

 doubt owing to the very strong cohesion 

 exerted between its particles. (Memoir 

 by Guyton, Annales de Chimie, t. 31. ; 

 or Abstract of it in Nicholson's Journal, 

 4to. viii. p. 298.) 



The appearances attending the combus- 

 tion of the diamond have been observed 

 with perhaps more accuracy by Sir George 

 Mackenzie, and the temperature requi- 

 site has been stated by him as less high. 

 A diamond cut and polished, when intro- 

 duced into a muffle previously heated red 

 hot, soon acquired the same redness as the 



VOL. IV. 



muffle, but in a few minutes more became 

 distinguished by a bright glow, and be- 

 gan to consume. A piece of plumbago 

 placed beside it exhibited a similar lu- 

 minous appearance, but it began at a 

 lower temperature. When the air waa 

 excluded iVom the muffle, both lost their 

 brightness; but it returned on the ad- 

 mission of the air, and was much in- 

 creased by blowing on them with a bel- 

 lows. To ascertain at what tempera- 

 ture the combustion of the diamond took 

 place, one of the pyrometrical pieces of 

 Wedgwood was placed with it in the 

 muffle. When both were perfectly red 

 throughout, the pyrometer was with- 

 drawn, and indicated 13 of Wedgwood's 

 scale. They were replaced, and the heat 

 increased until the glow appeared; it 

 was kept at this as equal as possible 

 until the diamond was consumed ; the 

 pyrometrical piece then indicated 14, 

 and in another diamond the heat requi- 

 site to produce the glow, and consume it, 

 was 15. These experiments are evi- 

 dently the most accurate tliat have been 

 made to ascertain this point; and in- 

 deed the temperature assigned by Guy- 

 ton was rather from conjecture than 

 experiment. Although they shew that 

 a less elevation of temperature is requi- 

 site for the combustion of the diamond 

 than was supposed, they still prove it to 

 be much higher than that which is requi- 

 site for the combustion of charcoal. 



Sir George Mackenzie, likewise, re- 

 peated and confirmed an experiment of 

 the French chemists, in which a piece of 

 soft iron was converted into steel by be- 

 ing heated with diamonds, in the same 

 manner as it would have been by being* 

 heated in the usual manner with charcoal 

 powder ; and his experiments are more 

 satisfactory, as having been made with 

 diamond in its purest state. (Nicholson's 

 Journal, 4to. vol. iv. p. 103.) 



The diamond is scarcely acted on by 

 any other agent than by oxygen, at an 

 elevated temperature. Bergman states 

 an experiment, from which it would ap- 

 pear to be capable of being partially 

 oxyded by sulphuric acid ; this acid, when 

 poured on the diamond powder, previous- 

 ly freed from impurities by digestion with, 

 nitro-muriatic acid, and evaporated to a 

 small quantity, becoming black, and de- 

 positing small pellicles, which take fire 

 on the approach of flame, and are con- 

 sumed. The other acids, according to 

 his observation, exert no sensible action 

 on it; nor docs it appear from the expe- 

 riments he made with soda (the mixture 



Y 



