PART III.

Alkalies and Neutral Salts.

619

acid, and 59 of base', with a small portion of carbonate oflime. The addition of sulphuric acid, as directed in the aboveformula:, abstracts 0'40 parts of the lime, so as to form an in-soluble sulphate of lime, and, involved in its mass, a solublesuperphosphate of lime, for the separation of which the di-gestion in vapour and the repeated effusions of boiling waterare ordered. The soda of the subcarbonate of soda, which isadded to the defecated and filtered solution, now unites withthe superabundant phosphoric acid, by which means the limeis again left combined with as ranch of this scid only as ren-ders it a neutral phosphate, which from its insolubility pre-cipitates and is easily separated from the phosphate of soda,which being soluble, remains dissolved in the water, and crys-tallizes on the subsequent evaporation of the filtered liquor.

There are some niceties in the manipulation of this processthat require to be noticed. In the first place, if too muchsulphuric acid be employed, sulphate of soda will be alsoproduced; and as four parts only of sulphuric acid are re-quired to decompose ten parts of phosphate of lime, both theabove formula? err in this particular; secondly, as the phos-phate of soda does not crystallize well without an excess ofbase, a little more subcarbonate of soda must be added than isrequired simply to neutralize the excess of acid of the super-phosphate : and lastly, the evaporation must not be carriedquite to the formation of a pellicle, as in this case the crystal-lization is indeterminate, and the whole often concretes into

an irregular mass.

Qualities. — This salt has a purely saline taste, resemblingvery much that of common salt. Its crystals are large, regular,transparent, rhomboidal prisms, terminated by three-sidedpyramids, having a specific gravity of 1-333, and efflorescingon exposure to the air. It is soluble in three parts of water at60°, and in two parts of boiling water; and undergoes thewatery fusion when heated. Its constituents, according toThenard, are, in 100 parts, 19 of soda, 15 of phosphoric acid,and 66 of water: and according to Berzelius 20"33 of acid;17-67 of base, and 62-80 of water. Muriate of barytes, lime,and magnesia, decompose this salt; and by the strong acidsit is converted into biphosphate of soda.

1 Vauquelin.

2 A cheaper mode of preparing this salt has heen given by M. Funeke, aGerman chemist. He adds to the matter of calcined bones diffused in water, justenough dilute sulphuric acid to saturate the small portion of carbonate of lime italways contains. When the effervescence ceases, the whole is dissolved in nitricacid, and as much sulphate of soda added to the solution as of bone ashes used.The whole is then distilled to recover the nitric acid; and the phosphate of soda isseparated from the residue, which is a mixture of sulphate of lime and phosphateof soda^ by solution and crystallization.