PHOSPHATE OF LIME.

359

combined properties of chalk and spices (p. 72). It is therefore antacid,aromatic, and stimulant. It is frequently added to the ordinary chalkmixture in diarrhoea, and is employed on various other occasions wherespices are indicated. The dose of it is from 10 grains to a drachm.

Catcis Phos’phas.—Phosphate of Lime.

History. —Sclieele, in 1769, discovered phosphate of lime in bones.

Natural History . —Phosphate of lime is found in both kingdoms ofnature.

(a.) In the inorganized kingdom. —It is a constituent of the mineraltermed Apatite, and of some mineral waters; as those of KarlsbadSprudel, and of Franzensbrunn, near Eger.

( b.) In the organized kingdom. —It has been found in some plants, andmuch more frequently and copiously in animals. Thus it constitutesthe principal part of the earthy matter of the bones of the vertebrata, anda portion of the crusts of the articulata.

Preparation.— Phosphoric acid combines with lime in several pro-portions, forming basic, neutral, and acid salts. The compound usedin medicine is a sub- or f phosphate of lime. When obtained by cal-cining bones in an open vessel, it is called earth of bones (terra ossium )or bone-ash (ossa usta ulba; o. deusta; o. ad albedinem usta; o. calcinata;spodium album), and contains some carbonate of lime and other mat-ters mixed with it. If bone-ash be digested in diluted hydrochloricacid, and caustic ammonia added to the filtered solution, phosphateof lime, free from carbonate, is thrown down in a very minute stateof division, and when washed and dried, it constitutes the precipitatedphosphate of lime ( calcis phosphas preccipitatum) of the Dublin Pharma-copoeia. When the horns ( cornua ) of the deer ( cervus ) are calcined in aan open vessel until they become perfectly white, and the residual ash(sub-phosphate of lime) prepared by elutriation (as creta praeparata)we obtain burnt hartshorn ( cornu ustum, Ph . L.; cornu ustumprceparatum).

Properties. —Snbsesquiphospliate of lime is white, tasteless, odour-less, insoluble in water, but soluble in nitric, hydrochloric, and aceticacids, from which solutions it is thrown down unchanged, in composition,by ammonia, potash, and their carbonates. When exposed to a veryintense heat, it fuses, and undergoes no other change. The primaryform of the crystals of apatite (native subsesquiphosphate of lime) is thesix-sided prism.

Characteristics. —It is known to be a phosphate by its solubility inhydrochloric acid, and its being again thrown down as a white preci-pitate when the acid solution is supersaturated with caustic ammonia.If it be digested in a mixture of sulphuric acid and alcohol, sulphate oflime is precipitated, and an alcoholic solution of phosphoric acidobtained. The acid may then be recognised by the tests for it alreadymentioned (p. 253). If the precipitated sulphate of lime be dissolved inwater, the solution may be known to contain lime by the tests beforedescribed for the calcareous salts (p. 343). The subsesquiphosphate oflime of bones is distinguished from the neutral phosphate by its fusingwith greater difficulty, and dissolving more readily in hydrochloric acid.A very delicate test of the neutral phosphate is its crystallizing fromhydrochloric acid by evaporation (Wollaston, Phil. Trans, for 1797,p. 396 & 397).