289 
promoting the reduction of metals, and in giving to them their 
peculiar lustre, at a temperature even below that which the atmos- 
phere ordinarily possesses*. 
Hence it appears probable, at least, that the formation of the 
native sulphurets may take place, independent of the action of fire : 
and M. Proust, and our celebrated countryman, Mr. Davy, are of 
opinion, that the native sulphurets are actually formed, in conse- 
quence of a similar decomposition of different solutions of metals, 
by their combination with hydrosulphurets. It must, however, be 
remarked, that some of the metals are not thus precipitated by the 
addition of sulphuretted hydrogen alone; since when the metals 
are reduced to their minimum of oxygen, in consequence of its sub- 
traction by the hydrogen, they retain the last portion of it with a 
considerable degree of power, and are thereby prevented from en- 
tering into union with sulphur. The addition, however, of an earth, 
an alkali, or the carbonaceous matter, so abundant in the earth, 
takes from the metal this portion of adhering oxygen, leaving it 
pure, and free to enter into combination with the sulphur. In 
justice to the supporters of the Vulcanian theory, it must be also 
remarked, that essentially different properties, both physical and 
chemical, distinguish the pyrites, or native sulphurets, from the 
artificial or factitious. Their crystalline forms, their peculiar splen- 
dour, and their irridiscent investiture, yield matter, indeed, for per- 
tinacious argument, on both sides of the question. But, surely, the 
circumstance of these crystals being found, often, fast imbedded in 
so combustible a body as bitumen, speaks strongly in favour of 
their aqueous origin. Jet is frequently found containing them, or 
being closely invested by them, and at the same time manifesting 
no marks of having been acted on by heat ; which would surely 
have been the case, if their formation, which must have been at the 
* An Essay on Combustion, by Mrs. Fulhame, p. 178. 
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VOL. I. 
