ARGILLA vitriolata (alum) native; contaminated by ſulphur and vitriolic acid.
At the places about Wedneſbury and Bilſton, in Staffordſhire, where the coal pits are on fire, this ſubſtance ſublimes to the ſurface, and may be collected in conſiderable quantity during dry or froſty weather. I cannot be certain that this is a true chemical union, but the eye cannot diſtinguiſh the parts. Perhaps the ſulphur volatilizes the alum and ſo becomes intimately mixed with it. The exceſs of vitriolic acid keeps it in a deliqueſcent ſtate.
I believe a ſimilar compound ſubſtance ſublimes at the Solfaterra near Naples. W.
ARGILLIA vitriolata (alum) native, contaminated by vitriol of cobalt. In the mines of Herregrund and Idra this may be ſeen, ſhooting out into long ſlender filaments. Perhaps this is the trichites of the Greeks. Diſſolved in water it immediately betrays the preſence of vitriolic acid, upon the addition of terra ponderoſa ſalita (muriatic acid ſaturated with heavy earth.) By the addition of phlogiſticated alkali a precipitate of cobalt is thrown down, which makes a blue glaſs with borax or microcoſmic ſalt.
CUPRUM vitriolatum (vitriol of copper) contaminated by iron.
FERRUM vitriolatum (vitriol of iron) contaminated by nickel.