Experiments upon Diamond, Anthracite and Plumbago. 35 1 



ous distinct but very minute scintillations were darted from 

 it in every direction, and I could see the minute cavities and 

 projections which I have mentioned, forming every instant. 

 In this experiment I gave the diamond but one heat of about 

 a minute, but on examining it with a magnifier, I was sur- 

 prised to find, that only a very thin layer of the gem, not 

 much thicker than writing paper remained, the rest having 

 been burnt.* 



I subjected the anthracite of Wilkesbarre, Penn. to 

 similar trials, and by heating it very gradually, its de- 

 crepitation was obviated. It was consumed, with almost 

 as much rapidity, as the diamond; but exhibited, during 

 the action of the heat, an evident appearance of being 

 superficially softened; I could also distinctly see, in the 

 midst of the intense glare of light, very minute globules 

 forming upon the surface. These when examined by 

 a maghifier, proved to be perfectly white and limpid, and 

 the whole surface of the anthracite exhibited, like the dia- 

 mond, onl}' with more distinctness, cavities and projections 

 united by flowing lines, and covered with a black varnish, 

 exactly like some of the volcanic slags and semi-vitrifications. 

 The remark already made, respecting the diamond, appears 

 to be equally applicable to the anthracite, i. e. that its want 

 of conducting power, is the reason why it is not melted by 

 the deflagrator. and its combustibility is the sole obstacle to 

 its complete fusion by the compound blow-pipe. 



I next subjected a parallelopiped of plumbago to the com- 

 pound flame. It was consumed with considerable rapidity, 

 but presented at the same time, numerous globules of melt- 

 ed matter, clearly distinguishable by the naked eye, and 

 when the piece was afterwards examined, with a good glass, 

 it was found richly adorned, with numerous perfectly white 

 and transparent spheres, connected also by white lines of the 

 same matter, covering the greater part of the surface, for the 



*In Tilloch's Phil. Magf. ior November 1821, Vol. 58, page 386, I observe 

 the follov.'ing- notice by Mr. John Murray. " By repeatedly exposing a 

 diamond to the action of the oxy-hydrogen blow-pipe in a nidus of magnesia, 

 it became as black as charcoal, and split into fragments which displayed the 

 ccnchoidal fracture. 



It will be found, thst this gem affixed in magnesia soon, flies off in minute 

 fragments, e'shibiting the imnre'^s of the cocchoidal form. 



In lately exposing the diamond fixed on a support of pipe-clay, to the igni- 

 ted gas, I succeeded in compietely indenting it : — examined it after the ex- 

 perim«Dts, it exhibited proofs of having undergone /imon." 



