12 Of Simple Earths. r. Calcareous earths feel dry, meagre, and harlh, when in a loofe or femi-induratedßate; and this property they communicate to other earths in the fame flale, when they conÜitute at leaft 40 or 50 per cent. of the whoie. When iri a ftony ftate they are never hard enough to ftrike fire with fleel; and they imprefs this property on Compounds in a ftony ftate, in which they enter in the proportion of 30 per cent. 2. Barytic earth, when not the principal in- gredient in a compound, has fcarcely occurred in any confiderable proportion. Its high fpecific gravity it undoubtedly communicates, but the porous flrudure of the compound may be fuch as to conceal it. 3. Magnefia feels fmooth; in a ftony ftate it never occurs fingle, but it imprefles a charader of Imoothnefs and unfluofity on all compounds in which it has not the oppofite charaders of calcareous earth to encounter, and into which it entcrs in the proportion of 18 to 20 per cent. It alfo gives a greenilh caft to ftones, and a' bias towards a fibrous, ftriatcd, or ftaty ftruc- turc, and fome luftre, particularly of the filky kind. 4. Argill is alfo foft, fmooth, and unftuous to the feel; it ftrongly abforbs water, and bar- dens when heated. In loofe or femi-indurated mixtures it imparts thefe properties to calcareous earths only when it exceeds them in quantity. With magnefia it can have no ftruggle; but, on filiceous earths, it imprefles its charaders in fome degree, even when it amounts only to 13 or 14 per cent. of the whole. In ftony compounds, if it exceeds 2,0 per cent. and is mixed with mag nefia, it gives a bias to a ftaty or lamellar flrue- ture.