No. 4.] CHEMICAL AND FARM MANURES. 151 



Nitrogen in nitrates, 100 



Nitrogen in sulfate of ammonia and raw Peruvian 



guano, 83 



Nitrogen in dried blood, horn meal, castor pomace 



and green plants, ....... 65 



Nitrogen in horn meal, dried fish and meat,* . , 53 



Nitrogen in wool dust and stable manure, ... 25 



Nitrogen in leather meal, 15 



These are only approximate figures ; they are neverthe- 

 less of much value as indicators of the variation in the 

 possible eflectiveness of such manures. Experiments by 

 Lindsey have shown that treatment of leather with sulfuric 

 acid increases greatly its assimilability. This treatment tends 

 to break up the structure of the leather, and, if continued 

 long; enouffh under favorable circumstances would chano'e 

 the nitrogen to sulfate of ammonia, when its efficiency would 

 of course correspond with that material. Th. Pfeifier has 

 recently obtained much higher results for dried blood than 

 those given by Wagner, and finds that it approaches more 

 nearly sulfate of ammonia as a source of nitrogen. In fact, 

 his results accord much more closely than Wagner's with 

 those secured in Rhode Island in pots sunk in the ground, 

 filled with natural soil and subjected to approximately nor- 

 mal conditions of temperature and moisture. In these 

 Rhode Island experiments, letting 100 represent the assimi- 

 lability of the nitrogen of nitrate of soda, the following 

 data were obtained : — 



* Tankage contains on an average about 6 to 7 per cent of nitrogen, which is 

 often present to a considerable extent as meat associated with tendons, etc., and 

 with bone. 



t Upon this soil it poisoned the plants. 



