148 Analysis and Valuation of Manures [243-246 



ANALYSIS OF MANURE CAKES 



243. Such substances as rape cake, castor-bean cake, and 

 damaged cotton and linseed cakes are often used as manures. 

 The principal manurial constituent is, of course, nitrogen, but 

 in addition to this there is always a certain quantity of phos- 

 phoric acid in the ash usually combined with an alkali metal. 



244. Method of Analysis. 



Burn. Treat ash with HC1. Filter. 



Precipitate. Weigh as 

 sand. 



Filtrate. Add ammonia and calcium 

 chloride. Filter, and weigh pre- 

 cipitate as Ca 3 P 2 Q 8 . 



245. Moisture, nitrogen, and organic matter are estimated 

 as in guano. 



246. Sand and Calcic Phosphate.— Two grams of the 

 substance are weighed out in a platinum dish and burned, with 

 the precautions described in the analysis of feeding cakes. 

 The ash is transferred to a small beaker, and dissolved in about 

 20 c.c. of strong hydrochloric acid. The insoluble portion is 

 filtered off, washed with hot water, burned as described under 

 the estimation of sand in mineral phosphates, and weighed. 



The filtrate from the sand contains the phosphoric acid, 

 together with lime and alkalis. Of course this phosphoric 

 acid may be determined either by the citric acid or the 

 molybdate method, but it is customary to determine it by the 

 simple method indicated in the last table. The liquid must be 

 raised to the boiling-point, about 10 c.c. of the ordinary labora- 

 tory solution of calcium chloride added, then excess of ammonia. 

 The precipitate of calcium phosphate so formed must be 

 filtered rapidly, washed, and weighed as Ca 3 P 2 8 . 



From this weight the amount of phosphoric acid may be 

 calculated, or the result may be set out in this form : 



