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5. A specific gravity, reaching from, 2,16to 2,31.

6. A degree of hardness, such as to admitbeing scraped by the nail.

7. When heated nearly to redness, it calcines;and if then it be slightly sprinkled with water,it again concretes and hardens.

8. It promotes putrefaction in a high degree.

Of the six families of this species I shall de-scribe only one; namely, that which has beenmost advantageously employed as a manure.Descriptions of the other live should he foundin treatises of mineralogy. It is called fibrousgypsum.

Its colours are grey, yellowish or reddish, orsilvery white, or light red, or brownish yellow,or striped with one or more of these dark co-lours. It is composed of fibres or stria;, eitherstraight or curved, parallel or converging to acommon centre, sometimes thick, sometimesfine and subtile, adhering to each other, andvery brittle: its hardness such as to admit beingscraped with the nail: commonly semi-trans-parent ; in some, often in a high degree.

Ashes. Sifted coal-ashes, those of peat and

c