V.] MINERAL SUPER-PHOSPHATES. 39 



mineral phosphates and bone, whereby economy of 

 manufacture has been coupled with high quality. 



73. Another source of phosphate must also be 

 noticed, and that is known as bone ash. This has 

 been largely imported from South America, and is the 

 ash of the bones, used for fuel to melt the tallow 

 obtained from the herds of cattle slaughtered for their 

 tallow, hides, and horns. Many thousand head of 

 cattle were thus slaughtered, and as fuel was scarce, 

 the bones were so employed. For many years the 

 ash was not of any value, and immense quantities had 

 been accumulated, when the bone ash suddenly be- 

 came of great value by reason of its new use for the 

 manufacture of super-phosphate of lime. Bone ash has 

 since then been found valuable for many other manu- 

 factures. 



74. It has been explained (66) that bi- calcic 

 phosphate is produced in the soil by the gradual 

 decomposition of bones, and it may be added that the 

 growth of vegetation arising from this use of bones is 

 always of a most healthy character. Liebig's 

 important discovery, which was intended to obtain 

 the same results more rapidly, has been made use of 

 very extensively, but it has been recognized that we 

 have to a great extent "over-manufactured" our phos- 

 phate, by converting it entirely into a mono-calcic 

 phosphate. This more rapid process has not, how- 

 ever, accomplished the same result, and the un- 

 healthy character of vegetation often testifies to this 

 fact. 



75. There is every reason to believe that the mono- 

 calcic phosphate, by reason of its solubility, is easily 

 distributed through the soil, but that it is too acid in 

 its character to enter into the circulation of plants. 

 If a manure containing mono-calcic phosphate be 

 added to a calcareous soil, the lime with which it 

 comes in contact combines with it, and the mono- 

 calcic phosphate becomes changed into a bi-calcic 



