the Diamond from Anthracite and Graphite. 343 
ton had previously supposed that it was “probably an unc- 
tuous substance coagulated.’ Such bodies, however, as am- 
ber, the resins, bitumen, wax, fat, &c., &c., contain so large a 
proportion of other ingredients than carbon, particularly of 
hydrogen, the number of equivalents of which frequently ex- 
ceeds that of the equivalents of carbon, that it is difficult to 
suppose any process by which the hydrogen could be extracted 
so as to leave the carbon. In anthracite, on the other hand, 
we have little foreign matter to extract, and yet sufficient to 
disturb the previous molecular arrangement, of the mineral. 
I do not attempt to indicate at what temperature (except 
that it must be comparatively low), and under what exact 
circumstances, anthracite may change into diamond. One 
point, however, seems to deserve notice. It may seem diffi- 
cult to concede that the action of oxygen on the surface 
of a mass of anthracite can determine the evolution of bodies 
from a depth within its substance. Whatever difficulties, 
however, may attend the conception of the process, it is 
quite certain that masses of anthracite may be changed by 
heat into coke or carbon, throughout their entire substance, 
whilst they increase in solidity and density. We may either 
suppose, accordingly, that anthracite is so porous that the 
oxygen of the air can penetrate to the centre, or that the 
superficial oxidation of the mineral determines a trans- 
ference of the particles more deeply seated to the surface, 
where they are oxidised. The last reference will be bet- 
ter understood if I adduce a case in point. A bar of steel, 
é.e., @ compound of iron and carbon, if raised to a red heat, 
and exposed to a current of air or oxygen, may be changed 
into a bar of iron ; yet during the process carbon must have 
travelled from the centre of the bar to the surface, or oxygen 
must have travelled from the surface to the centre and back 
again, before the carbon could have been volatilised as car- 
bonie oxide. By a similar process, hydrogen and the like 
might be extracted from a mass of anthracite. As for the 
non-volatile ingredient or ash, I may, on the one hand, notice 
that crystallising substances are notoriously possessed of the 
power of extruding heterogeneous or foreign matter ; and, on 
