COMMERCIAL FERTILIZER MATERIALS 445 



244. Dried blood and tankage.^ — ^Both. of these fertilizers 

 are paeking-honse products. The former is obtained by dry- 

 ing the blood from the slaughtering pens. It comes on the 

 market as a homogeneous blackish to dark greyish material, 

 often slightly moist and with a characteristic odor. Its eon- 

 tent of ammonia (NHg) ranges from 10 to 16 per cent., de- 

 pending on the grade of the fertilizer. It often contains 

 traces of phosphoric acid (PsOg).^ 



Tankage is a mixture of various refuse materials from the 

 slaughter-houses, such as blood, hair, scraps of meat, and hide 

 and bone. It is generally steam-cooked and part of the gela- 

 tin and fat removed. It is variable in composition, carrying 

 from 5 to 10 per cent, of NHg and from 3 to 8 per cent, of 

 PoOg. The phosphoric acid is contained in the bone and is 

 in the form of tricaleium phosphate [Ca3(P04)2]. Tankage 

 is easily distinguished from blood meal by its heterogeneous 

 cJiaracijer. 



When added to a soil, both blood and tankage undergo rapid 

 decomposition, ammonification, and finally nitrification. Such 

 fertilizers are, therefore, very effective in the late spring and 

 summer. For early application, however, a material such 

 as sodium nitrate is much better, since a biological transfor- 

 mation is unnecessary in order that it may be immediately 

 utilized by the plants. 



245. Otiher organic nitrogenous fertilizers. — ^Below will 

 be found the composition of a number of other organic ma- 

 terials that have been or are still used as fertilizers. Only two 

 need explanation. Guano consists of the excrement and car- 

 casses of sea fowls, the composition depending on the climate 

 and position in which it is found. Guano from an arid region 

 contains ammonia, phosphoric acid, and potash. Under 

 humid conditions only the phosphoric acid remains in any 



*Fry, W. H., MenUfication of Commercial Feriilizer Materials; IT. S. 

 "Dept. Agr., Bui. 97, 1914. 



^The composition of commercial fertilizers is commonly expressed in 

 terms of ammonia (NHg), phosphoric acid (P2O5), and potash (KsO), 



