52 AMERICAN MANURES. 



On the subject of the action of superphosphate 

 of lime in soils, and its relative value compared 

 with insoluble phosphoric acid, as contained in 

 bone-dust, coprolites or mineral guano, we can- 

 not do better than give an extract from Konna's 

 exhaustive report on that subject, as follows : 



" What takes place, in fact, when super- 

 phosphates are presented to the soil ? Coming 

 into contact with the alkalies, or the earthy 

 alkaline bases, the phosphoric acid in excess 

 combines with them, and phosphate of lime is 

 precipitated in a gelatinous condition, this being 

 the one in which a sparingly soluble substance 

 enters more freely into solution. Gelatinous 

 phosphate of lime dissolves readily even in the 

 feeble carbonic acid. When it presents itself, 

 however, in the form of coprolites, solution is 

 effected with the greatest difficulty. From this 

 it may be seen, how little profitable it is, to use 

 powdered coprolites, otherwise than upon new 

 clearings and first ploughing**, or upon soils in 

 w r hich probably free acids can act upon them, so 

 that they may then be able to yield to vegeta- 

 tion by degrees a small quantity of phosphoric 

 acid. Such coprolytic powder does not satisfy 

 the demands of an advanced and progressive 

 agriculture, that is, immediate results, but only 

 effects, for which one is compelled to wait ten, 

 yea, twenty 3 T ears. 



