Commercial Value of Artificial Manures. 
281 
The fact is, the commercial value of soluble phosphate of lime, 
like that of many other materials, depends in some measure on 
tlic source from which it is derived and the nature and the 
amount of other substances with which it is associated. Thus, 
soluble phosphates cannot be produced at as low a price when 
made from bones as from mineral phosphates. Then why not 
make it in the cheapest possible form ? is a question which 
naturally suggests itself, but which is answered by the fact that 
in many instances bones partially dissolved in oil of vitriol pro- 
duce a better practical result on the turnip-crop on light soils 
than a mixture containing an equivalent amount of soluble 
phosphate made from coprolites and insoluble bone-phosphate. 
We thus see that it is not enough that there should be a certain 
amount of soluble and insoluble phosphate in a turnip-manure, 
but that the very source from which the fertiliser is obtained 
affects its agricultural as well as its commercial value. 
A superphosphate containing, say, 15 or 18 per cent, of soluble, 
15 per cent, of insoluble phosphate in the shape of bone, and 
2^ per cent, of nitrogen, can be made much cheaper by pro- 
ducing in the first place the soluble phosphate from coprolites, 
and mixing the coprolite superphosphate afterwards with bone- 
dust and a certain quantity of shoddy, or a similar nitrogenous 
refuse material, than by making it entirely from bones. But as 
superphosphate prepared from bones has a better effect in the 
field and costs the maker more money, and thus has a higher 
commercial value than a manure which on analysis furnishes 
the same amount of soluble and insoluble phosphate and nitrogen, 
the constituents of a bone-superphosphate, and amongst them 
soluble phosphate of lime, must have a higher commercial value 
in this combination than in a mere mixture of dissolved copro- 
lites, bone-dust, and a nitrogenous refuse matter. 
Again, up to 28 or 30 per cent, of soluble phosphate (i, e., 
bone-earth rendered soluble by acid), may be produced in a 
superphosphate simply by mixing phosphatic materials with a 
certain quantity of sulphuric-acid ; but if a much higher pro- 
portion of soluble phosphate is required, recourse must be had 
to more complicated and expensive chemical processes ; and 
these processes, of course, add to the expense at which the 
soluble phosphate is obtained in highly concentrated manures, 
such as Messrs. Burnard, Lack, and Go's. Concentrated Super- 
phosphate, which contains no less than 44 per cent, of soluble 
phosphate. 
Notwithstanding the increased expense in producing the soluble 
phosphate in a highly concentrated superphosphate, it may be 
good policy and economical to the consumer to prepare such con- 
centrated fertilisers for exportation or for application in localities 
