ORGANIC NITROGEN FERTILIZERS 115 



advantage that the resulting material contains a small 

 quantity of lime, and is thereby improved as a fertilizer. 

 The rate at which decomposition takes place in the soil is 

 more rapid with lime-treated blood than with ferric sulphate 

 coagulated blood. 



Meat Meal. Butchers' waste of all kinds is first cut up 

 into pieces and boiled in vats. The material can be con- 

 veniently extracted with benzine for the recovery of fat, 

 and a material which is of greater mammal value is thus 

 produced. Much of the ordinary commercial meat meal is 

 really a mixture of meat and bones, and is made during the 

 process of the manufacture of extract of meat. A large 

 amount of this material is put upon the market as Fray 

 Bentos guano, which is manufactured in Uruguay in con- 

 nection with the manufacture of extract of meat and pressed 

 beef. It contains 6 % of nitrogen and 10-20 % of 

 phosphates. 



Hoofs, Horns, and Leather. Hoofs and horns make a 

 very useful form of fertilizer. When they are in their 

 natural condition they decompose very slowly in the soil 

 and have little value, but by treatment they can be converted 

 into valuable manures. The hoofs of ruminants are nearly 

 pure protein, and contain 13-14 % of nitrogen. Waste 

 whalebone and the refuse from whale fisheries also come 

 into this group. These materials are best either roasted or 

 steamed. When horn is roasted without overheating it 

 becomes drier, and as it cools it becomes brittle, and is thus 

 easy to crush. Steaming may be done in a cylindrical vessel 

 with a false bottom, which can be charged with the horn 

 from a man-hole in the top. Steam is then blown through 

 the bottom and allowed to escape through a safety valve. 

 After treatment for about an hour, the steam is cut off, 

 and the steamed horn removed from a man-hole at the 

 bottom. The horn has thereby become brittle, and can be 

 easily ground up. Various leather wastes are also utilized 

 in the same way. 



When hides are received at a tannery for the purpose 

 of manufacturing leather, they are first washed and soaked 



