214 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 
because it contains three equivalents of lime to one of phosphoric 
acid. The soluble phosphate is called " monobasic," because it 
contains one equivalent of phosphoric acid to one of lime. 
Insoluble tribasic 
Soluble monobasic 
Phosphoric acid . . | 
Lime, 
Lime 
Lime 
Phosphoric acid . . | 
Water 
Lime 
Water 
When sulphuric acid is added to the tribasic phosphate, two 
parts of lime are removed, and their places taken by two of 
water, which is always present in sulphuric acid, converting the 
tribasic into monobasic phosphate of lime. The liberated two 
parts of lime unite with two parts of the sulphuric acid to form 
gypsum. 
A soluble superphosphate is too acid to enter at once into 
the food of plants, but when mixed with the soil it undergoes a 
preparatory change, which weakens its acid character and in- 
creases its diffusive powers. 
Dr. Voelcker states that the absorption of phosphates is more 
rapid and complete in exact proportion to the amount of lime 
present in the soil. 
Lime is intimately connected with the fixation of soluble 
phosphates. It acts by combining with the acid phosphates to 
form a less soluble but more neutral compound called *' dibasic " 
phosphate of lime : — 
Less soluble dibasic 
( Lime 
Phosphoric acid . 
, Water 
[ Lime 
Uses of Superphosphate. 
The value of superphosphate will greatly depend on the 
presence of available nitrogenous matter, or of potash, in the 
soil. Two parts of superphosphate by weight to one of potash, 
applied in the proportion of 3 to 5 cwts. per acre, is said to be a 
good manure for Potatos, Turnips, Beet-roots, &c., but its value 
