230 PHOSPHATE FERTILIZERS 



sour soil. In such an application there probably would not 

 result more than 100 pounds of calcium oxide combined as 

 carbonate, not enough for any immediate effectiveness. 



176. Summary. — Phosphate fertilizers are all of them 

 forms of calcium phosphate with varying degrees of avail- 

 ability depending in large measure on the form of com- 

 bination. Monocalcium phosphate, found in acid phosphate, 

 dissolved bone-black, and other sulphuric acid-treated phos- 

 phate products, is the most quickly available and in general 

 the best to use. Tricalcium phosphate, found in rock phos- 

 phate and bones not treated with sulphuric acid, is the 

 least soluble. In rock phosphate it is available only when 

 mixed with decomposing organic matter, and is best used 

 with manure, or on acid soils containing large amounts of 

 organic matter. 



Raw bones are unavailable on account of the presence of 

 fat and ossein which prevent the solvent action of soil 

 moisture on the phosphate, they themselves decomposing 

 very slowly. Steamed bone, however, in the form of steamed 

 bone-meal is a good fertilizer of fairly rapid availability. 

 Here the fat and most of the ossein have been removed by 

 high-pressure steam, leaving the tricalcium phosphate in a 

 condition easily ground and readily attacked by the soil 

 moisture. Bone-black has had all the organic matter 

 destroyed by heat in the absence of air, leaving only tri- 

 calcium phosphate mixed with some carbon. After this 

 is employed to clarify such things as sugar solutions it is 

 used as a fertilizer to good advantage. 



Basic slag is a manufactured product having the phos- 

 phorus in the tetra- and pentacalcium form, in the latter 

 compound also united with some silica. The compounds 

 are fairly soluble in the water and carbon dioxide of the soil, 

 leaving a residue of calcium carbonate or bicarbonate which 

 has a beneficial alkaline effect, especially on acid soils. 



REFERENCES 



See references at end of Chapter VIII. 



