VI

PREFACE?.

new compound; which, notwithstanding the pungent tasteos the one ingredient, the corrosive acidity of the other,and the solubility of both, proves insipid and indissoluble,and which therefore, separating from the water, renders itat first milky, and on standing settles to the bottom, inform of powder or small crystals, of the same generalproperties with the native gypsums or plaster-of-parisstones.

If this powder be ground with inflammable matter, aspowdered charcoal, no action happens between them, howexquisitely soever they be mixed: the two powders con-tinue gypsum and charcoal, and may be in great measureparted from one another by means of water, the charcoalpowder remaining for a time suspended in the fluid, whilethe heavier gypsum settles. On exposing the mixture toa proper degree of heat, a strong chemical affinity beginsto take place : the acid quits the lime, and unites withthe inflammable principle of the coal, forming therewithanother new compound, common brimstone, which, likethe former, proves insipid, and indissoluble in watery li-quors, though in other properties remarkably different;melting in a small degree of heat into a red fluid; in a some-what greater heat, if air is excluded, rising into the upperpart of the vessel unaltered; on the admission of air chang-ing into a blue flame, with a suffocating volatile acid fume,which by air and moisture returns into the original, inodo-rous, ponderous, vitriolic acid.

By mixing the brimstone with iron filings, a fresh trans-position is produced; and as in the preceding cafe the actionis excited by sire, so in this it is excited by water. The

mixture,