Chap. IV. Earths, and Eart/ij/ Salts.

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applied to medical use; and its strong affinity for water andalcohol fits it for the rectification of alcohol and ether.

Counu ustum. Lond.Burnt Horn.Burn pieces of horn in the open fire, until they become per-fectly white; then reduce them to powder, and prepare itin the same manner as is directed for chalk.

Pulvis COItNU cervini usti. Dub.Powder of Burnt Hartshorn.Burn pieces of hartshorn till tbey become perfectly white;then reduce them to a very fine powder.

The pieces of horn generally employed in this operationare those left after distillation.

In the burning of hartshorn, a sufficient fire, and the freeadmission of air are necessary. The potter's furnace wasformerly directed, for the sake of convenience; but any com-mon furnace or stove will do. Indeed, too violent a heatmakes their surface undergo a kind of fusion and vitrification,which both prevents the internal parts from being completelyburnt, and renders the whole less soluble. If the pieces ofhorn be laid on some lighted charcoal, spread on the bottomof the grate, they will be burnt to whiteness, still retainingthei' - original form.

According to the analysis of Merat Guillot, hartshorn con-sists of 27. gelatine, 57.5 phosphate of lime, 1. carbonate oflime, and there was a loss of 14.5, probably water. Now, asthe gelatine is destroyed by burning, and the water expelled,the substance which remains is phosphate of lime, mixed withless than two per cent, of carbonate of lime. Fourcroy andVauquelin have analysed bones more accurately, and foundthat they contain phosphate of magnesia, iron, and manga-nese, and that human bones contain less of the first of these,and more of the two others than animal bones, which is pro-bably owing to the constant excretion of phosphate of mag-nesia in human urine. In human bones there are also tracesof alumine and silex.

Medical use. —From its white earthy appearance, it wasformerly considered as an absorbent earth. But since it hasbeen accurately analysed, that idea has been laid aside, andits use has been suggested as a remedy in rickets, a disease inwhich the deficiency of the natural deposition of phosphate oflime in the bones seems to be the essentia], or, at least, themost striking symptom. Mr Bonhomme, therefore, gave it to