442 
The specific gravity of soft cast iron is about 6.94, of the hard 
7.54; the average may therefore be considered as 7.24 containing about 
5 per cent. of carbon; but the plumbago resulting from it, when perfectly 
dry, floated not only on water, but, for an instant, even on alcohol. With 
the view of freeing it entirely from the air included in its pores, a portion 
weighing 226.2, grains was boiled in distilled water, by which, not- 
withstanding it deposited two grains of ochre, it gained 214.8 grains. 
Its specific gravity was then taken, and was found to be 1.26. It 
appears therefore that nearly all the metallic iron had been gradually 
converted into a soluble muriate, which, as it was formed, was removed 
by the passage of the vessel through the water; leaving only the carbon 
in the interstices of which it originally existed. The average specific 
gravity of the Borrowdale graphite is 2.13 and it contains 41 per cent. 
of metallic iron; the inferior specific gravity of the artificial specimen 
made it probable that it contained still less, which was confirmed by 
deflagration, in the usual mode, with nitre. The exact quantity seems 
however of no importance; as there can be no doubt that the same 
process which had removed so great a portion of the iron, would, if con- 
tinued, have left nothing but the carbon. For the agent being evidently 
Galvanism, exerted in precisely the same manner as in its recent application 
by Sir H. Davy, would have acted upon the iron, through the intermedium 
of the carbon, until it were entirely removed. 
In regard to the useful application of this substance, there can be 
little doubt that in many cases it may be substituted for the coarser kind 
of plumbago; but it is so much softer that it cannot be used for the 
purposes of drawing, unless as a crayon. The colour of its streak on 
paper.is not so dark as that of plumbago, and instead of presenting 
a continuous line, the streak appears, when examined by a lens, to be 
composed of minute detached portions of carbon, intermixed with specks 
of metallic iron. i 
In the ist Volume of the Annals of Philosophy, Dr. Henry of 
Manchester has given an account of a similar substance found in a 
