SOURCES OF FERTILIZING MATERIALS 51 



pose ; it should be used only as a stock food, and thus enrich the home-made 

 manure. 



Castor pomace is a valuable source of nitrogen in limited localities. It 

 usually contains nearly 6 per cent, of nitrogen, decays rapidly in the soil and 

 is soon available as plant food. 



Another product of the great western slaughter houses is tankage. This 

 is composed of the dried *and pulverized waste matters from the slaughtering 

 of animals, and is of a very varying nature. One form of the more concen- 

 trated tankage may contain as much as 12 or more per cent, of nitrogen, while 

 other samples will not have more than 4 to 5 per cent, of nitrogen, but a 

 larger percentage of phosphoric acid than the concentrated form. The price 

 of tankage, of course, varies with its composition, and a low-priced article is 

 always one that has the least percentage of nitrogen. It is, therefore, im- 

 portant to look after the analysis claimed for each sample. 



About the most worthless form in which one can get organic nitrogen 

 is in the meal made from leather scraps. Analysis will show that this con- 

 tains a large percentage of nitrogen, yet it is almost worthless to the farmer, 

 since the leather so long resists decay in the soil. The making of a fertilizer 

 in which leather is used as a source of nitrogen, should be looked upon simply 

 as a fraud. In the same class should be placed wool and hair waste, which 

 can only be made available by dissolving in sulphuric acid. 



From the fat rendering establishments, where the dead animals from the 

 large cities are utilized, there comes dried meat; which has value for nitrogen 

 nearly as high as that of the dried blood from the slaughter houses. 



Formerly there was a rich deposit of natural guano with a very high per- 

 centage of nitrogen on the Chincha Islands, on the coast of Peru. But this 

 was long ago exhausted, and though we have occasionally so-called Peruvian 

 guano offered for sale, it is far inferior to the old article; as it comes from 

 localities where rain has washed out a large part of the nitrogen, and consists 

 mainly of insoluble phosphate of lime. The exhaustion of the old Peruvian 

 guano beds gave the first great impulse to the manufacture of commercial fer- 

 tilizers, so that now the natural guanos make little show on the market, and 

 being largely of a phosphatic nature are mainly used by the manufacturers of 

 fertilizers. 



When any of these organic matters, containing nitrogen, decay, the first 

 result is the formation of the hydride of nitrogen, or ammonia, from the com- 

 bination of hydrogen and nitrogen. But green leaved plants, as a rule, do 

 not use nitrogen in the form of ammonia. The bacteria in the soil which 

 bring about what is known as nitrification, break down the ammonia and form 

 the nitrogen into a nitrite. Another form of bacteria then takes up the work 



