226 



On Superphosphate of Lime. 



£. s. d. 



Sulphate of lime 49-8 (say 50) per cent,, half a ton at 20s. 0 10 0 

 Insoluble phosphate of lime (9-79 per cent.) 220 lbs. 



at 0 13 9 



Nitrogen -68 per cent., equal to '82 per cent, of ammonia, 



or 18^ lbs., at 6c? 0 9 3 



Making . £1 13 0 



as the value of all the ingredients, with the exception of the 

 bi-phosphate. Deduct this sum from 71., and we have 5Z. as the 

 value of 280 lbs. of bi-phosphate of hme, or about 4^d. per lb. 

 This 280 lbs. of bi-phosphate represents, and will form in the 

 soil, 408 lbs. of neutral phosphate in the precipitated or active 

 state, which will therefore cost or be of the value of 2id. or 

 nearly 3d. per lb. 



These calculations are necessarily crude, and open to many 

 sources of error ; they must be received in a general sense 

 only, and as approximations to the truth. If, however, they serve 

 to give us a general notion of the worth of the substance in 

 question, they will be most useful in their application to indi- 

 vidual cases. 



The sample No. 4 was placed amongst those of superior 

 quality from its large percentage of nitrogen coupled with a 

 fair proportion of soluble phosphate; in common with Nos. 

 2 and 3, it has evidently been made from bones and sulphuric 

 acid only. It may be worth while to place its money-value in 

 comparison with the more mineral superphosphate No. 10. It 

 contains — 



£. s. d. 



31*29 per cent, of gypsum, which in a ton amounts to 



700 lbs., of the value of 0 6 3 



20*43 per cent, of neutral phosphate amounts to 457 lbs,, 



of the value of 18 7 



3*24 per cent, of nitrogen, equal to 3*94 per cent, of 



ammonia, or 88 lbs. in the ton, value . . .240 

 9*92 per cent, of bi-phosphate, or 222 lbs., which, at 



4|(i. per lb., has a value of . . . . . 3 18 7 



£7 17 5 



This sample, being made from bones and acid alone^ would 

 probably be sold at 8/. per ton, so that, in fixing the value of 

 bi-phosphate of lime at 4^d. per lb., we 'do not seem to have 

 erred very greatly. It will occur, perhaps, to the reader that 

 the insoluble phosphate of lime unacted on by the acid will have 

 a different value according to the source from which it is derived ; 

 that when^ for instance, the manure has been made from bones 

 or African guano, the phosphate, although not actually soluble 

 in water;, will be much more readily available to vegetation than 



