38 
Ahsoiytion of Phosphate of Lime ; and 
As long^ as bones only Avcre treated with sulphuric acid, a 
large proportion of the insoluble phosphate of lime^ — the chief con- 
stituent of the incombustible part of bones — was left unchanged 
in its chemical composition. Such partially dissolved bones, 
containing seldom more than 8 or 10 per cent, of soluble phos- 
phate of lime, nevertheless produced a more beneficial and rapid 
effect upon the crops than is explicable by the action of soluble 
phosphate alone, so that the results obtained must be in part attri- 
buted to the bone-dust having become softened by this treatment, 
and hereby rendered more available for the use of plants. . 
Satisfied with these results, agriculturists Avere content to 
purchase bone-superphosphate, which contained, comparatively 
speaking, little soluble, and much insoluble, phosphate. But 
when necessity compelled the manufacturer to substitute mineral 
phosphates for bone-dust, complaints of a deterioration in 
the quality of manure were heard on all sides. In many 
instances these complaints were not without foundation ; for in 
reality superphosphate lost much in value when bone-dust was 
first replaced by insoluble mineral phosphates. The remedy for 
this evil, however, was soon found to consist in rendering the 
mineral phosphate as completely soluble as possible. By the 
use of a large proportion of acid, our best makers at present 
convert nearly the whole of the insoluble phosphates in coprolites, 
apatite, &c., into bi- (or soluble) phosphate of lime ; for expe- 
rience has taught them that mineral phosphates unaltered in 
chemical composition, are of little more practical value to root- 
crops than sand ; and that, therefore, it is a waste of material to 
leave mineral phosphates in a turnip-manure, in an insoluble 
condition. 
Such samples appear to produce, though not on all soils, as 
good a crop of roots as can be desired ; nor have we any reason 
to doubt their efficacy on account of their origin. Since soluble 
phosphate is a definite chemical compound of one equivalent 
of lime and one equivalent of phosphoric acid, it would be r.ither 
strange if this were not so. As in the case of pure sulphate 
of ammonia it matters not whether it be prepared from bones or 
from gas-water, why, in like manner, may not a biphosphate of 
lime, of the same composition and properties, be obtained indif- 
ferently either from bones or from mineral j)hosphates ? 
Soluble phosphate unquestionably is the most valual)lc con- 
stituent of commercial superphosphates ; for experience has 
shown that with its percentage, the efficacy of this class of 
manure generally rises or falls ; and though on light land 
th(! use of other fertilizers is desirable for tin? turnip-crop, still 
in many cases nothing more or less is required than a lair pro- 
portion of soluble phosphate of lime. 
