Professor Sllliman on the Fusion of Plumbago. \ 25 



on the eilge of the focus, and in several instances were stud- 

 ded around so thickly, as to resemble a string of beads, of 

 which the largest were of the size of the smallest shot ; others 

 were merely visible to the naked eye, and others still were mi- 

 croscopic. No globule ever ^appeared on the point of the 

 plumbago, which had been in the focus of heat ; but this point 

 presented a hemispherical excavation, and the plumbago there 

 had the appearance of black scoriae or volcanic cinders. These 

 wei'e the general appearances at the copper pole occupied by 

 the plumbago. 



On the zinc pole, occupied by the prepared charcoal, there 

 were very peculiar results. This pole was, in every instance, 

 elongated towards the copper pole, and the black matter, ac- 

 cumulated there, presented every appearance of fusion, not 

 into globules, but into a fibrous and striated form, like the half 

 flowing slag found on the upper currents of lava. It was 

 evidently transferred, in the state of vapoui', from the plum- 

 bago of the other pole, and had been formed by the carbon 

 taken from the hemispherical cavity. It was so different from 

 the melted charcoal, described in my former communications, 

 that its origin from the plumbago could admit of no reasonable 

 doubt. I am now to state other appearances which have ex- 

 cited in my mind a very deep interest. On the end of the 

 prepared charcoal, and occupying, frequently, an area of a 

 quarter of an inch or more in diameter, were found numerous 

 globules of perfectly melted matter, entii'ely spherical in their 

 form, having a high vitreous lustre, and a great degree of 

 beauty. Some of them, and generally they were those most 

 remote from the focus, were of a jet black, like the most per- 

 fect obsidian ; others were brown, yellow, and topaz coloured : 

 others still were greyish white, like pearl stones with the trans- 

 lucence and lustre of porcelain ; and others still, limpid like 

 flint glass, or in some cases like hyalite or precious opal, but 

 without the iridescence of the latter. Few of the globules upon 

 the zinc pole were perfectly black, while very few of those on 

 the copjier j)ole were otherwise. In one instance, when I used 

 some of the very jjure English plumbago, (sawed from a cabinet 

 sjiecinien, and believed to be from Borrowdale,) white and 

 transparent globules were formed on the copper side. 



When the points were held vertically^ and the plumbago np- 

 permosf, no globules were formed on the latter; and they were 

 unusually numerous, and almost all black, on the opposite pole. 

 When the })oints were exchanged, plumbago being on the zinc, 

 and charcoal on the copper end, very few globules were formed 

 on the ])linnl)ago, and not one on the charcoal : this last was 

 rapidly hollowed out into a hemispherical cavity, while the 



pliuubago 



