In the preceding review we have taken of bituminoussubstances, there is a link found wanting to furnish a con-nection in the chain of being between bituminous andother substances where ignition is discovered to be aperceptible quality, and which constitutes their leadingcharacteristic. This hiatus is supplied by the articlePyrites , of which we now propose to speak. Pyrites isa mineral substance, in which sulphur appears to form achief constituent, and is mixed in certain indefinite propor-tions with various metals. Its chief properties are, that ifexposed to atmospheric air, and particularly if water bebrought in contact, it spontaneously takes fire. It is aspecies of matrix to many metals ; silver occasionally hasbeen found in it, but more generally copper and iron.
The appearance of pyrites manifests a metallic lustre ofthe colour of the metal which is discovered to enter intotheir composition : other than those possessing copper oc-casionally assume the appearance of gold. They are fre-quently found in coal-mines, and occasionally aluminous saltenters into their composition.
To the accidental commixture of water whilst in a mineralstate, is ascribed by Mr. Parkinson , the appearance ofwhat we call mineral charcoal. Chymical analysis infersthis from metals being discovered in their composition, andfrom other ascertained tacts. Dr. Thomas Plot, in hisNatural History of Staffordshire, p. 142, relates that atEaland in Yorkshire , one Wilson had piled up many cart-loads of pyrites in his barn for some secret purpose, per-haps to extract the gold. The roof being faulty, and ad-mitting rain-water to fall copiously in among them, theyfirst began to smoke, at last took fire, and burnt like coals,so that the town was considerably disturbed and alarmed.
Dr. Jordan, in his Essay upon Mineral Waters , speak-ing of the properties which coals possess when they containmuch of the pyrites, or as the colliers call them, coal-metal,of heating, and even kindling upon the gradual accessionof moisture, or the effusion of water upon them, states,that several such accidents have happened at Newcastle;and he particularly mentions a circumstance of this kindhaving occurred in London , at Puddle-dock. M. Fourcroystates, that a quantity having been placed in a yard, atParis, they first began to smoke, w hich gradually increased ;as rain fell, they hurst out into a flame, and alarmed thewhole neighbourhood, who feared a conflagation wouldensue. In the Philosophical Transactions , vol. lii. p. 119,a curious and very circumstantial account is rendered by