1 :, i AfjriruUurn! Chemistry. 



rock, bones and tankage. They contain from 25 to 30 per cent 

 of phosphoric acid. Ground into a fine powder, the first three 

 are sometimes sold under the name of "floats," which on account 

 of its fineness of division has given beneficial results, especially 

 when mix<-;l with stable manure or applied to soils rich in organic 

 matter. 



Soluble phosphate of lime. This substance is known under 

 several names, as "one-lime phosphate, " "acid-phosphate," ''su- 

 per-phosphate," "acidulated rock," etc. It is the result of 

 treating rock phosphates or bones with sulphuric acid. By this 

 process the sulphuric acid combines with 2 parts of the lime, 

 forming sulphate of lime or gypsum. This leaves a compound 

 which contains 1 part of lime and 2 parts of water, in combination 

 with the 1 part of phosphoric acid which was contained in the 

 tri-calcium phosphate. This substance is soluble in water, read- 

 ily diffuses in the soil, and is in the most available form for direct 

 use by the plant. A good sample of acid-phosphate contains 

 about .1 6 per cent of phosphoric acid. While easily dissolved by 

 water, it is not leached out, as several constituents of the soil such 

 as humus, lime, iron and aluminum compounds have the power 

 of fixing and retaining it for the use of plants. 



Reverted phosphate of lime. In making super-phosphate the 

 whole of the insoluble phosphate is not acted upon. 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 to 

 what is called ' ' reverted " or " gone back ' ' phosphate. It is also 

 known as "di-calcium" phosphate, "citrate-soluble," and "pre- 

 cipitated phosphate." In composition, this material falls be- 

 tween the tri-calcium and mono-calcium phosphates. It is quite i 

 insoluble in pure water, but can be dissolved by weak acids, and 

 by water containing carbonic acid, or by ammonium .salts. As 

 the soil moisture contains salts in solution, as well as carbon di- 

 oxide, this phosphate is readily assimilated by plants ..and is con- 

 sidered an available form. This form of phosphate is considered 



