COMMERCIAL MANURES. 203 



State of such extreme division, as to be, for practical purposes, 

 almost as useful as if made into superphosphate. 



The difference between a bone manure thus prepared, and a 

 " Super Phosphate" (properly so called) is, that in the latter the 

 phosphate is rendered " soluble" by a chemical change in its pro- 

 portions, effected by means of acid ; while in the former there is 

 simply a physical subdivision effected by means of a chemical 

 action which decomposes the cement which holds together the 

 extremely minute molecules of phosphate in the bone. To give 

 some idea of the extent of this subdivision let me say, that, were 

 a cubic inch of bone divided into a million of little cubes, (each 

 measuring- the one-hundredth of an inch on either side) every one 

 of them would be more than a thousand times larger than the par- 

 ticles as they exist in bone. Now, because the degree of solubility 

 of substances difficult of solution is greatly enhanced by being 

 made fine, you can readily see why I stated that bone thus treated 

 was nearly as useful as if made into superphosphate. 



The next commercial fertilizer which I mention, is Peruvian 

 guano. This, as formerly imported, contained from 15 to IT per 

 cent, of ammonia, but latterly from 11 to 13 per cent. The high 

 price it bears is chiefly due to this content ; for of all the manurial 

 agents which the farmer has occasion to buy, the dearest is nitrogen 

 in such form or combination that plants can appropriate it to their 

 use. Peruvian guano contains a small percentage of potash; also 

 about one half as much phosphate as raw bone ; but as before 

 remarked, its chief commercial value is due to its nitrogen. 



Like other ammoniacal manures, its principal use is for grain and 

 grass crops ; and the chief profit from its use is realized upon lands 

 rich in mineral constituents. 



Peruvian guano cannot be continuously used and the crops sold 

 ofi", without rapid impoverishment of the land, except upon soils rich 

 in dormant mineral resources. A considerable portion of the land 

 in the Southeru States is of this character, and hence the high 

 repute in which Peruvian guano continues to be held there. 



But to use it with impunity in New England, it is imperatively 

 necessary, that the bulk of all which is grown by it should be con- 

 sumed upon the farm and returned to the soil in manure. 



For general use among us, it is found that the proportions of 

 ammonia and the phosphates in Peruvian guano, are not those 

 which may be employed to advantage. There is too much of the 

 former in proportion to the amount of the latter. 



