212 



Oil Superphosphate of Lime. 



manufacturer, because, as I have reason to know in many instances 

 that have come to my notice, he is apt to think that he has done 

 his duty if he employs the prescribed quantities of phosphoric 

 substances and acid to dissolve them, making; it a matter of con- 

 venience to himself as to what he subsequently adds to dry up the 

 mixture and render it portable and fit for use ; and should he 

 choose chalk for this purpose, which not unfrequently happens, it 

 is clear that the consumer, whilst he has the advantajje of sub- 

 division, loses that of distribution. They are important to the con- 

 sumer ; inasmuch as attention to this point will preserve him from 

 mixing the superphosphate with those substances which are likely 

 to prevent its equal distribution through the soil. To this subject^ 

 however, we shall have occasion to recur hereafter. 



Having now endeavoured at some length to show that the object 

 of the manufacturer should be the production of a highly soluble 

 phosphate of lime, and that the consumer should so employ it that 

 the reconversion into the insoluble condition may take place only 

 in the intimate recesses of the soil ; and having further insisted 

 upon the distinction between mere subdivision and distribution^ 

 the former of which is, in my opinion, only half complete without 

 the latter, I shall pass on to describe very shortly the substances 

 employed in the manufacture of superphosphate, and to show what 

 circumstances should guide us in their use, leaving to a later part 

 of the paper to offer any practical suggestions that may arise from 

 a careful consideration of the various principles involved. 



It is plain from what we have already said that superphosphate 

 of lime may be made from sulphuric acid and any substance con- 

 taining phosphate of lime. The substances that are or can be 

 employed in the manufacture are — 



Bones, either boiled or raw, 

 Bone ash. 



Bone or animal charcoal, 

 Guano, especially the African variety, 

 The so-called coprolites of the crag and chalk for- 

 mations, 



And the phosphorite or mineral phosphate of Estre- 

 madura and the United States. 



Some other substances are occasionally employed, not, indeed^ 

 as sources of phosphate of lime, but under the impression that 

 they improve the manure, or because they are useful in drying it 

 up and bringing it to a proper consistency. We shall take another 

 opportunity of showing in what way they are employed. 



I shall separately describe in as few words as possible the 

 phosphoric substances above enumerated, and, after giving ana- 

 lyses of some of them, I shall point out what quantity of acid is 



