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bonate of lime in the bones of man and other animals,who obtain it from the substances on which they feed.
171. Phosphate of lime is easily decomposed by themore powerful acids, such as sulphuric acid and muriaticacid: in the former case an insoluble sulphate will beformed, and phosphoric acid left in solution; and in thelatter, a clear solution will be obtained containing phos-phoric acid and muriate of lime, a salt which is veryeasily soluble in water.
172. Magnesia is an earth somewhat similar to lime,but far less common and abundant. It occurs usuallyin connexion with lime, forming what is called magne-sian limestone, which is a mixture of carbonate of limeand carbonate of magnesia.
173. The commonest forms in which magnesia is foundare the carbonate, the sulphate, the muriate, and thephosphate. The carbonate is sometimes found nativepure, but by far more frequently it is mixed with thecarbonate of lime or limestone, the properties of whichit considerably modifies. When the carbonate of mag-nesia is strongly heated, it parts with its carbonic acid,and the pure earth magnesia is obtained.
174. This earth is almost insoluble in water, and farless strongly caustic than lime ; it also has less affinityfor carbonic acid, so that when left exposed to the air,it does not, like lime, rapidly become converted into car-bonate by absorbing carbonic acid from the air, butremains for a long time caustic; and hence when a mag-nesian limestone is burnt in a limekiln, the quicklime