ARTIFICIAL AND CONCENTRATED MANURES. 75 



What is called " high-grade blood " is red in color, and 

 is quite uniform in composition, ranging from twelve to 

 fourteen per cent of nitrogen. This form of blood is 

 used largely in the arts, hence the supply for manurial 

 purposes is limited : lower grades are in greater supply ; 

 these are darker in color, vary widely in composition 

 and physical character, and frequently contain, as im- 

 purities, moisture, hair, bone, etc. ; the two latter, to be 

 sure, contain nitrogen, but in forms less useful than in 

 the blood. 



Dried Meat, or Azotine. This material is proba- 

 bly, next to blood, the most important source of organic 

 nitrogen. It is obtained by separating the meat from 

 the bones, extracting the fat by steaming or solvents, 

 and drying and grinding into powder. It is usually in 

 excellent mechanical condition, and when free from bone 

 is quite uniform in composition, containing on the aver- 

 age twelve per cent of nitrogen. 



Tankage. Tankage is the dried refuse from slaughter- 

 houses and butcher-shops, and is composed of various 

 wastes as offal, skin, bone, hair, and meat; it contains 

 both nitrogen and phosphoric acid, though usually classed 

 as a nitrogenous product. 



The source from which this material is derived indicates 

 at once that it must be variable in composition ; it shows 

 wide ranges in its content of both nitrogen and phosphoric 

 acid. These variations in composition are largely due to 

 the quantity of bone contained in it. The larger the pro- 

 portion of bone, the lower the percentage of nitrogen, and 

 the smaller the proportion of bone, the higher the content 

 of nitrogen. What is called "concentrated tankage" is 



