180 Prof. Silliman on the Fusion of Plumbago , fyc. 
inch or more in diameter, which appeared to be owing to the iron, 
remaining from the combustion of the carbon of that part of the 
piece, and which, being now oxidized to a maximum, assumed the 
usual colour of the peroxide of that metal. 
“ In various trials, the globules were formed very abundantly on 
the edge of the focus, and, in several instances, were studded 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 microscopic. 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 cin- 
ders. These were the general appearances at the copper pole occu- 
pied by the plumbago. 
“ On the zinc pole, occupied by the prepared charcoal, there 
were very peculiar results. This pole was, in every instance, elon- 
gated towards the copper pole, and the black matter accumulated 
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 vapour, from the plumbago 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 com-« 
munications, that its origin from the plumbago could admit of no 
reasonable doubt. I am now to state other appearances, which have 
excited in my mind a very deep interest. On the end of the pre- 
pared charcoal, and occupying frequently an area of a quarter of an 
inch or more in diameter, were found numerous globules of perfect- 
ly melted matter, entirely 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 perfect obsidian ; others were brown, yellow, 
and topaz coloured ; others still were greyish- white, like pearl- 
stones, with the translucence and lustre of porcelain : and others still 
limpid like jlint-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 
copper pole were otherwise. In one instance, when I used some of 
the very pure English plumbago (believed to be from Borrowdale)^ 
white and transparent globules were formed on the copper side. 
^ I detached some of the globules, and partly bedding them in a 
handle of wood, tried their hardness and firmness ; they bore strong 
pressure without breaking, and easily scratched, not only flint-glass, 
but window-glass, and even the hard green variety, which forms the 
aquafortis bottles.” 
Having refitted the deflagrator with new zinc coils, so as to 
make it act with great energy, Professor Silliman obtained the 
following resultSj by using, plumbago upon both poles. The 
parallelepipeds were one-fifth of an inch in diameter, and about 
J or 2 inches long ; and, when brought into contact, they trans* 
