PHOSPHATE OF LIME.

Nelson Evening Mail, Volume XLII, Issue XLII, 18 June 1907, Page 1

PHOSPHATE OF LIME.

This substance is known under several names — as mono-calcium phosphate or one-lima phosphate, acid phosphate, superphosphate. The process of treating rock phosphate or. bones with sulphuric acid is, as stated, for the purpose of converting the tri-calciuta phosphate in these materials into the soluble mono-calcium phosphate. By this process the sulphuric acid wilh two parts of lime, forming sulphate of lime, forming sulphate of lime or gypsum ; the -water of -the acid taking the place of the_ lime which has b«en removed. This gives a compound which contains one-part of lim& and two parts of watc&vin combination with the one part of phosphoric acid "which was contained in the tri-calcium phosphate. This. substance is very soluble in water, and readily diffuses in phe soil. ' In making this material the. whole: of the insoluble phosphate is not acted tipon, for to render all of it soluble -would require the addition of an access of snlphuric acid which would prove injurious to plant life. The tri-calcium phosphate which remains' after the treatment with acid, when left in contact with a comparatively large amount of soluble phosphate, causes a_ reversion of some of the soluble material, which gives more or less of the other form of phosphate called "reverted" or. "goneback" phosphate. The quantity of soluble phosphate present in acid phosphate varies somewhat, but it should contain from 13 to 16 per cent., . the amount depending chiefly upon the materials from 'which' it has been made. Acid phosphate carries a considerable quantity of gypsum; each lOOlbs containing usually iwtween HKahd "60 lbp. This material has 6ome_ value as an indirect fertilising materia] f J«ahd .its presence in the phosphate' should, : not be neglected, especially '-by 'those who often think it necessary; .to use gypsum in making different fertiliser . mixtures, or in making complete fertilisers which contain acid phosphate. -, The^.solnbje phosphate, being very " sbliible,' ' -Mo therefore readily diffused in the soil, is the most valuable fonft .of/ phosphate for plant food. Although"* it i is. easily dissolved by the . soil water, it is not leached out as several constituents of the soil, such as humus, lime,"irbn, and aluminium compounds, have the power n{ fixing and retaining it for the use of plants.