Phosphas Sodae. Edin. Phosphate of Soda

"Take of bones, burnt to whiteness and reduced to powder, ten pounds; sulphuric acid, six pounds; subcarbonate of soda, a sufficient quantity. Mix the powdered bones with the sulphuric acid in an earthen vessel; then add nine pounds of water, and again mix: keep the vessel in a vapour bath for three days; after which, dilute the matter with nine pounds more of boiling water, and strain through a strong linen cloth, pouring boiling water gradually over it, until the whole of the phosphoric acid be washed out. Set the strained liquor apart, that the impurities may subside, from which pour it off, and evaporate it to nine pounds. To this liquor, separated from its impurities, and heated in an earthen vessel, add a warm solution of subcarbonate of soda, until the effervescence cease: then strain and set the liquors aside, that crystals may form. These being removed, add to the liquor, if necessary, a little subcarbonate of soda, that the phosphoric acid may be accurately saturated; and dispose it, by evaporation again, to yield crystals, as long as these shall be produced.

Finally, let the crystals be preserved in a well-closed vessel."

Dublin.

"Take of burnt bones, reduced to powder, ten parts; sulphuric acid of commerce, seven parts. Mix the powder with the sulphuric acid in an earthen vessel; add, gradually, seven parts of the water, and agitate the mixture. Digest for three days, adding from time to time more water, lest the materials should become dry, and continue the agitation; then pour over them five pints of boiling water, and strain through a linen rag, pouring on, at intervals, boiling water, until all the acid be washed out. Set the liquor apart that the impurities may subside, from which decant it, and evaporate it to one half; then add three pounds ten ounces of carbonate of soda (dissolved in eight parts of warm water); filter, and obtain crystals by repeated evaporation and cooling. If the salt be not perfectly pure, it may be purified by. repeated solution and crystallization.

Syn. Phosphate de Soude (F.), Phosphosaures Natrum (G.), Fosfato di Soda(I.).

When bones are burnt to whiteness, the residue is chiefly phosphate of lime, 100 parts of which consist of 41 parts of acid, and 59 of base1; and with a small portion of carbonate of lime. The addition of sulphuric acid, as directed in the above formula, abstracts 0.40 parts of the lime, so as to form an insoluble sulphate of lime, and, involved in its mass, a soluble superphosphate of lime, for the separation of which, the digestion in vapour and the repeated effusions of boiling water are ordered. The soda of the carbonate of soda, which is added to the defecated and filtered solution, now unites with the superabundant phosphoric acid, by which means the lime is again left combined with as much of this acid only as renders it a neutral phosphate, which from its insolubility precipitates, and is easily separated from the phosphate of soda, which being soluble, remains dissolved in the water, and crystallizes on the subsequent evaporation of the filtered liquor.

1 Vauquelin.

There are some niceties in the manipulation of this process that require to be noticed. In the first place, if too much sulphuric acid be employed, sulphate of soda will be also produced; and as four parts only of sulphuric acid are required to decompose ten parts of phosphate of lime, both the above formulae err in this particular; secondly, as the phosphate of soda does not crystallize well without an excess of base, a little more carbonate of soda must be added than is required simply to neutralize the excess of acid of the superphosphate; and, lastly, the evaporation must not be carried quite to the formation of a pellicle, as in this case the crystallization is indeterminate, and the whole often concretes into an irregular mass.1

Qualities. - This salt has a purely saline taste, resembling very much that of common salt. Its crystals are large, regular, transparent, oblique, rhombic prisms, having a specific gravity of 1.333, and efflorescing on exposure to the air. It is soluble in three parts of water at 60°, and in two parts of boiling water; and undergoes the watery fusion when heated. Its constituents, according to Thenard, 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. Mitscherlich makes them 1 eq. of acid = 55.4 + 1 of soda = 31.3 + 12 of water = 108. Chloride of barium, lime, and magnesia decompose this salt; and by the strong acids it is converted into biphosphate of soda.

1 A cheaper mode of preparing this salt has been given by M. Funcke, a German chymist. He adds to the matter of calcined bones, diffused in water, just enough dilute sulphuric acid to saturate the small portion of carbonate of lime it always contains. When the effervescence ceases, the whole is dissolved in nitric acid, 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 is separated from the residue, which is a mixture of sulphate of lime and phosphate of soda, by solution and crystallization.

Medical properties and uses. - It is a mild cathartic, excellently adapted for children, and others who have a fastidious taste. It may be given dissolved in gruel, or broth, made without salt, by which its taste is very effectually covered. The dose is from 3 vj. to ij. Although phosphate of soda was known before 1740, at which time it was described by Haupt, under the name of sal mirabile perlatum, yet it was not introduced into medical use as a purgative until about thirty years since, when it was recommended by Dr. George Pearson of London.