364 HANDT-BOOK OF HUSBANDRY. 



cipitate. In order to separate these impurities the precipitate is dis- 

 solved in a few drops of hydrochloric acid, and the acid solution 

 carefully evaporated to complete dryness. The hard, dried resi- 

 due is again made acid with muriatic acid, a little water is then 

 added, and the liquid passed through a small filter, on which are 

 left insoluble traces of the silica originally thrown down with 

 magnesia. A few drops of citric acid having been added to the 

 acid solution, with a view of keeping any traces of iron in solu- 

 tion, strong ammonia is finally added, which throws down a 

 second time phosphate of magnesia and ammonia, now free from 

 silica and oxide of iron. The precipitate is collected, washed with 

 ammonia water, dried, burned in a platinum crucible or capsule, 

 weighed, and the phosphoric acid calculated from the weight of the 

 tri-basic phosphate of magnesia left on burning. 



*' Following this plan and the precautions here indicated, the 

 smallest amount of phosphoric acid in a soil can be determined 

 with great precisions If the magnesia precipitate be not redis- 

 solved and freed from silica, as pointed out, a higher percentage 

 of phosphoric acid necessarily is obtained than the actual quantity 

 which the soil contains. 



*' Clover-roots. — The roots from i square foot of soil were 

 cleaned as much as possible, dried completely at 2I2°, and in that 

 state weighed 240 grains. An acre consequently contained 

 1,493^ ^^^- °^ ^^'^^^ clover-roots. 



The clover-roots contained : — 



Dried at 412° Fahr. 



♦Organic matter 8" '3 3 



f Mineral matter (ash) 1 8 67 



loo-oo 



* Yielding nitrogen >"6jJ 



Equal to ammonia 1'98S 



f Including insoluble silicious matter (clay and sand) Wby 



" Accordingly, the clover-roots in an acre of land furnished 24^ 

 lbs. of nitrogen. We have thus : — 



lbs, of Nitrogen. 



In the 6 inches of surface soil 3>350 



In large clover-roots 24^ 



In second 6 inches of soil ',875 



Total amount of nitrogen in i acre of soil 12 inches deep. 5,249] 



Equal to ammonia 6,}74i 



