72 BOARD OP AGRICULTURE. [Jan., 



and only three-quarters as much nitrogen as our best qualities of 

 fine ground bone, while the price is by no means correspondingly 

 less, 



T have now rapidly enumerated the principal sources of supply 

 of phosphates for commercial fertilizers. First, Peruvian guano, 

 a thing by itself; a complete manure, containing sometimes as 

 much nitrogen as phosphoric acid, besides a supply of potash ; but 

 introduced here on account of its historical importance, and from 

 its connection with the phosphates which follow next. 



Second, the washed guanos, or phosphatic guanos. Baker, 

 Howland, and Jarvis Island guano — perhaps little Curasao, and 

 many others not spoken of ; all of them soft, fine, pulverulent, 

 and, we may suppose, more assimilable in their raw condition than 

 those which follow. 



Third, phosphorite and apatite; the former amorphous, the lat- 

 ter crystalline; both hard, and rocky, from the action of heat and 

 the pressure of surrounding strata — leaving it, in most cases, 

 questionable whether they were of animal origin, or whether they 

 are a part of the original earth-crust which has never been incor- 

 porated into plant or animal structure. 



And, fourthly, we have noticed some waste products of varying 

 assim liability, from bone-black, which, applied directly to land, 

 would be quite inert, to ground bone, which is very rapid in its 

 action. 



I have not time to speak of the super-phosphate manufacture, 

 nor does it fairly come within the scope of this lecture. We all 

 understand the theory of it. These hard phosphates, when groimd 

 and mixed with oil of vitriol, are decomposed, and their phos- 

 phoric acid becomes soluble in water, and so easily taken up by 

 plants. 



Messrs. Mapes & Co., H. J. Baker & Bro., and G. B. Forrester 

 offer brands containing from twelve to fifteen per cent, of soluble 

 phosphoric acid, and not more than one per cent, imdecomposed 

 phosphate, at a low figure ; but most so-called super-phosj)hates 

 have from one-quarter to three-quarters of their phosphoric acid in 

 an insoluble form, and no more effective agriculturally than the 

 raw material from which they were manufactured. There is no 

 apparent reason why soluble phosphoric acid, made from apatite or 

 South Carolina rock, is not just as serviceable on land as that from 

 bone — and, of course, it can be more cheaply produced; but if 

 from one quarter to three-quarters of the material employed is not 



