GENERAL PHYSICAL PROPERTIES OF EARTHS.

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brought that they are compound; we must therefore considerthem as simple bodies, which nature presents to us completelyformed, though one or more of them enters into the compositionof a great many bodies. They have a variety of properties whichare common to all.

GENERAL PHYSICAL PROPERTIES OF EARTHS.

Alb earths are dry incombustible bodies. They are insolublein water, and alcohol, or nearly so. They have little or no taste.Their specific gravity does not exceed 4. 9 . When perfectly purethey assume the form of a white powder, harsh to the touch.They are infusible. They are capable of combining with acids,when they form neutral salts. They are likewise disposed tounite with the alcalies, with sulphur, and phosphorus; with me-tallic oxids, and with each other, either tiy fusion or solution inwater.

Every one of these characters is not perhaps rigorously appli-cable to each of these bodies; but they all possess a sufficientnumber of them to render it useful to arrange them under oneclass.

Stones differ from earths principally in cohesion and hardness,and therefore are included under the same general name.