The mother source of phosphate of lime is supposed to be 

 the mineral known as apatite and found in various parts of the 

 world. Other mineral sources of phosphate of lime have been 

 found, more particularly in South Carolina, Florida and Ten- 

 nessee. All soils contain an abundant supply of phosphate of 

 lime, but as we have exhausted the available part, we must 

 supply it in some form or other. 



The original commercial source was bone, which is composed 

 of about 65% of phosphate of lime, the other 35% of the bone 

 being cartilage, fat, marrow, glue, water, etc. After the demand 

 for fertilizer had exhausted the supply of bone, the mineral 

 deposits of phosphate of lime were taken up, and it was found 

 that by grinding them fine and dissolving them in oil of vitriol 

 (sulphuric acid), the phosphate of lime was rendered available to 

 plants, and thus it helped to supply the "little balance" of this 

 ingredient necessary for crop production. The sources of phos- 

 phorus (phosphoric acid) and phosphate of lime are therefore 

 the bones from packing-houses, fisheries and market places 

 and the mineral deposits of phosphates in all parts of the world. 



It is believed that phosphoric acid is the most important 

 of the three principal elements of plant food, not because it is 

 the most required, for in the composition of the plant it is least 

 needed, but because it is a "catalyzer" as v/ell as a fertilizer. 

 In chemistry, a catalyzer is an element which assists in the 

 union of other elements without becoming a part of the union — 

 a sort of "go-between"; that is, besides furnishing the needed 

 phosphoric acid, it assists in the diffusion and assimilation of 

 other plant food ingredients. If phosphoric acid exercises a cata- 

 lytic action in the soil (and there is no doubt of it), the experi- 

 ments of Lawes and Gilbert, as well as results in practical crop 

 growing, indicate that it is the soluble phosphoric acid which 

 possesses this quality, and that the insoluble phosphoric acid does 

 not possess it at all. This in part explains v/hy superphosphates 

 (dissolved bone, dissolved bone black and acid phosphate) are 

 much superior to undissolved phosphates. 



Four Forms of Phosphate 



There are four forms of phosphate of lime, as follows: 

 4-lime phosphate — Tetra-Calcic — A by-product of steel manufacture. 

 3 -lime phosphate — Tri-Calcic — Mineral phosphates and bone. 

 2-lime phosphate — Di-Calcic — Reverted phosphoric acid. 

 1-lime phosphate — Mono-Calcic — Water soluble phosphoric acid. 



9 



Source 

 of 



Phosphoric 

 Acid 



Bone, 

 Composi- 

 tion of 



What 

 Is a 

 * Catalyzer' 



