[ 21 ] operation into a white powder, and if its folution ftrikes the tincture of violets green, it is alum. experiment XXIV. 58. If a faline fubftance has a bitter tafte, you may put into its folution a folution of any alkali whatfoever, which will turn the fame firft milky, then curdly, and at laft precipitate a white earth, which is a proof of its containing an epsom-salt, compounded of acid of vitriol and magnefia. section v. On Inflammable Subflances. EXPERIMENT XXV. £9. IF a mineral inflammable fubftance be found quite tranfparent, liquid, of no colour, of a fragrant fmell, extremely volatile and inflam mable, and attracting gold from its folution in aqua regis, it is called naphtha. EXPERIMENT XXVI. 60. If a liquid inflammable fubftance be found coloured yellow, brown, or even black, has a fragrant fmell, but will not take fire at a dif- tance, nor attract gold from its folution in aqua regis, it muft be petroleum. EXPERIMENT XXVII. 61. If an inflammable be only fomewhat liquid, like tar, and has a dilagreeable fmell, it is mountain-tar. C 3 EXP E-