1823.] Scientific Intelligence, 469 



were some interesting varieties in the phenomena. Tlie plumbago 

 being a conductor, the light did not accumulate as it did when the 

 support was lime, but permitted me distinctly to see the diamond 

 through the whole experiment. It was consumed with great rapi- 

 dity ; a delicate halo of bluish light, clearly distinguishable from the 

 blow-pipe flame, hovered over it ; the surface appeared as if softened, 

 numerous distinct but very minute scintillations were darted from it 

 in every direction, and I could see the minute cavities and pro- 

 jections which I have mentioned forming every instant. In this ex- 

 periment I gave the diamond but one heat of about a minute ; but on 

 examining it with a magnifier, I was much surprised 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 decrepitation 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 couM also distinctly see, in the midst 

 of the intense glare of light, very minute globules forming upon the 

 surface. These, when examined by a magnifier, proved to be per- 

 fectly white and limpid ; and the whole surface of the anthracite ex- 

 hibited, like the diamond, only 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 combusti- 

 bility is the sole obstacle to its complete fusion by the compound blow- 

 pipe. 



I next subjected a parallelopiped of plumbago to the compound 

 flame. It was consumed with considerable rapidity, but presented at 

 the same time, numerous globules of melted matter, clearly distin 

 guishable by the naked eye ; and when the piece was afterwards exa- 

 mined, 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 space of half an inch at and around the point, and presenting 

 a beautiful contrast with the plumbago beneath, like that of a white 

 enamel upon a black ground. 



In subsequent trials, upon pieces from various localities, foreign and 

 domestic (confined however to very pure specimens), I obtained still 

 more decided results ; the white transparent globules became very 

 numerous, and as large as small shot ; they scratched window glass — 

 were tasteless — harsh when crushed between the teeth, and they were 



* In Tilloch's Phil. Mag. for November 1821, vol. Iviii. p. 386, I observe the fol- 

 lowing notice by Mr. John Murray: — " By repeatedly exposing a diamond to the 

 action of the oxy-hydrogen blow-pipe in a nidus of inagnesia^ it became as black as 

 charcoal, and split into fragments which displayed the conchoidal fracture. 



" It wiU be found, that this gem affixed in magnesia soon flies off in minute frag- 

 ments, exhibiting the impress of the conchoidal form. 



" In lately exposing the diamond fixed on a support of pipe-clay, to the ignited gas, 

 I succeeded in completely indenting it : — examined it after the experiments, it exhi«t 

 bited proofs of having undergone /««iow." 



