Soluble vs. Insoluble Cane Manures. 341 
obtained in immense quantities) are rejected as worthless 
by agriculturists, and even the mineral form of phosphate 
of calcium, has a much lower commercial value than the 
animal variety, in consequence of its less ready solubility.* 
To ascertain the effect of hydrate of iron, alumina and 
lime on superphosphate, the following experiments were 
made with a sample of white, so-called pure clay, or 
kaolin, to which known proportions of the above sub- 
stances were added. 
Experiment III. — 250 parts of dried kaolin were 
shaken in a corked flask with 1000 of superphosphate 
solution. After five days the filtered liquid contained '92 
parts of phosphoric acid per 1000, showing that only 8 
per cent, of the acid had been removed by the clay. 
The latter was found on examination to contain a small 
quantity of iron, to which the loss of acid was probably 
due ; practically, however, the clay had little or no effect 
in fixing the phosphoric acid. 
Experiment IV. — 250 parts of dried kaolin were well 
mixed with 5 parts of slacked lime, and shaken at inter- 
vals with 1000 parts of superphosphate solution. After 
five days the liquid contained "84 of phosphoric acid per 
1000, showing that 15 per cent, of the acid had become 
insoluble. The lime used was ordinary Bristol lime, and 
like the clay, it was also found to contain a minute 
quantity of iron. It is highly probable that if clay, 
* " It is necessary to ascertain whether the phosphates are soluble 
in carbonic acid (calcium and other protoxides), and therefore assimil- 
able by plants, or insoluble in carbonic acid (iron and other sesqui- 
oxides), and therefore non-assimilable. For analytical purposes, 
carbonic acid may be replaced by acetic." Use of Superphosphates, by 
J. P. Deherain. Journ. Chem. Soc. Abstracts, 1884, 925. 
UU 2 
