314 TALKS ON MANURES. 



" Saltpetre, or nitrate of potash," said the Deacon, " does not 

 contain as much nitrogen as nitrate of soda." 



"And yet," said the Doctor, " if it could be purchased at the 

 same price, it would be the cheaper manure. It contains 46^ per 

 cent of potash, and on soils, or for crops where potash is needed, 

 we may sometimes be able to purchase saltpetre to advantage." 



" If I could come across a lot of damaged saltpetre," said I, 

 " that could begot for whaf it is worth as manure, I should like to 

 try it on my apple trees — one row with nitrate of soda, and one row 

 with nitrate of potash. When we apply manure to apple trees, the 

 ammonia, phosphoric acid, and potash, are largely retained in the 

 first fev; inches of surface soil, and the deeper roots get hold of 

 only those portions whicli leach tlirough the upper layer of earth. 

 Nitric acid, however, is easily w-ashed down into the subsoil, and 

 would soon reach all the roots of the trees." 



CnAPTER XXXVII. 

 BONE-DUST AND SUPERPnOSPIIATE OF LIME. 



Bone-dust is often spoken of as a phosphatic manure, and it has 

 been supposed that the astonishing effect bone-dust sometimes pro- 

 duces on old pasture-land, is due to its furnishing phosphoric acid 

 to the soil. 



But it must be remembered that bone-dust furnishes nitrogen 

 as well as phosphoric acid, and we are not warranted in ascribing 

 the good effect of bones to phosphoric acid alone. 



Bones differ considerably in composition. They consist essen- 

 tially of gelatine and phosphate of lime. Bones from young ani- 

 mals, and the soft porous parts of all bones, contain more gelatine 

 than the solid parts, or the l)ones from older animals. On the aver- 

 age, 1,000 lbs. of good commercial bone-dust contains 38 lbs. of 

 nitrogen. 



On the old dairy farms of Cheshire, whore l)one-dust produced 

 such marked improvement in the quantity and quality of tlie pas- 

 tures and meadows, it was usual to apply from 4,000 to 5,000 lbs 

 per acre, and often more. In other words, a dressing of bone-dust 



