90 Practical Farming 



black color. The red blood may contain as much as 15 

 per cent, of nitrogen. A similar and important source of 

 nitrogen is the dried and pulverized scrap from the fish- 

 oil factories, which contains 8 per cent, of nitrogen and 

 nearly as much of phosphoric acid. 



Another product from the slaughterhouses is what is 

 known as tankage. All the refuse animal scraps which 

 cannot be utilized as food for men are boiled dowTi and 

 dried and pulverized. Its value depends on the material 

 used, so that tankage varies greatly in the percentage of 

 nitrogen. Some manufacturers of fertilizers have used 

 ground leather scraps, wool and hair waste, and horns 

 as a source of nitrogen. These are of little value in a fer- 

 tilizer on account of their slow decay. 



A great source of nitrogen is cotton-seed meal, which is 

 the by-product in the manufacture of cotton-seed oil. 

 The pomace left after pressing castor-oil beans is also 

 pulverized and used in Kke manner. Cotton-seed meal 

 will contain from 7 to 8 per cent, of nitrogen and also some 

 phosphoric acid and potash. The best authorities, how- 

 ever, beheve that this meal should not be used as a fer- 

 tilizer direct, since its feeding value as a component part 

 of a v/ell-balanced ration for farm animals is greater than 

 its manurial value, while the larger part of the nitrogen 

 can still be recovered in the manure, and thus greater 

 profit will accrue to the farmer than by using it as a direct 

 manure. But all manufacturers of fertilizers use it very 

 largely in their mixtures. 



Formerly one of the chief sources of nitrogen was in 

 the Peruvian guano from the Chincha Islands in Peru. 

 But this deposit was long since used up, and the Peruvian 



