uj)on the Diamond, Anthracite, and Plumbago. 1 33 



jections united by flowing lines, and covered with a black var- 

 nish, exactly like some oF the volcanic slags and semi-vitrifi- 

 cations. The remark already made respecting the diamond 

 appears to be equally applicaljle to the anthracite, i. e. that its 

 want of conducting power is ihe reason why it is not melted 

 by the deflagrator, and its combustibility is the sole obstacle 

 to its complete fusion by the compound blowpipe. 



I next subjected a parallelepiped of plumbago to the com- 

 pound flame. It was consumed with considerable rapidity, 

 but presented at the same time numerous globules of melted 

 matter, clearly distinguishable by the naked eye ; and when 

 the piece was afterwards examined with a good ghiss, it was 

 found richly adorned with numerous perfectly white and 

 transparent sjiheres, connected also by white lines of tlie same 

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

 of \ an inch at and around the point, and presenting a beau- 

 tiful 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 speci- 

 mens,) I obtained still more decided results; the white trans- 

 parent 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 not magnetic. 

 They vely much resembled melted silex, and might be sup- 

 posed to be derived from impurities in the plumbago, had not 

 their appearance been uniform in the different varieties of that 

 substance, whose analysis has never, I believe, presented any 

 combined silex, and neither good magnifiers, nor friction of the 

 powder between the fingers, could discover the slightest trace 

 of any foreign substance in these specimens. Add to this, in 

 different experiments, I obtained very numerous perfectly 

 black globules, on the same pieces which afforded the white 

 ones. In one instance they covered an inch in length, all 

 aroimd ; many of them were as large as common shot; and 

 they had all the lustre and brilliancy of the most perfect black 

 enamel. Among them were observed, here and there, glo- 

 bules of the lighter coloured varieties. In one instance the 

 entire end of tlie jiarallelopiped of plumbago was occupied by 

 a single black globule. The dark ones were uniformly at- 

 ti'acted by the magnet, and I think were rather more sensible 

 to it than the plumbago which had been ignited but not melted. 

 "We know how easily, in substances containing iron, the mag- 

 netic susceptibility is changed by slight variations of tempera- 

 ture. I am aware, however, that the dark globules may con- 

 lain more irtin than llie i)lunibago from which they were de- 

 rived 



