4 Journal of Agricultural Research voi. xvii, no. t 



4. Total phosphoric acid. — Five cc. of the solution were digested 

 with 15 cc. each of sulphuric and nitric acids until colorless (nitric acid 

 was added from time to time when necessary), 20 cc. of water were 

 added, and the solution boiled in order to expel any oxids of nitrogen. 

 It was then diluted with water, a slight excess of ammonium hydroxid 

 added, after which it was rendered slightly acid with nitric acid, and 

 phosphorus determined (2). 



5. Inorganic phosphoric acid. — Ten cc. of tlie solution were 

 diluted with from 20 to 30 cc. of water, boiled three minutes, two drops 

 of acetic acid added, the boiling continued for a minute, cooled, and 

 diluted to 100 cc. The solution was then filtered, a 50 cc. portion 

 was made faintly alkaline with ammonium hydroxid, and the phosphoric 

 acid precipitated in the usual manner with magnesia mixture. After 

 standing for two hours or longer the precipitate was filtered off, washed 

 with water containing 2.5 per cent of ammonia, and dissolved in dilute 

 nitric acid. The phosphoric acid was then determined as in total phos- 

 phoric acid. 



6. Total nitrogen. — Nitrogen was determined by the Gunning 

 method, using 10 cc. of the solution. 



7. Soluble nitrogen. — A portion of about 15 cc. of the solution 

 was centrifuged until clear, the clear liquid poured off, and the nitrogen 

 determined in a 10 cc. portion. 



8. CoagulablE nitrogen. — Fifty cc. of the solution in a glass evapor- 

 ating dish to which 50 cc. of water were added were evaporated on the 

 steam bath to one-half volume; 0.5 cc. of a 10 per cent solution of acetic 

 acid was added, heating was continued for 15 minutes, the coagulable 

 albumen was filtered, washed, and nitrogen determined in the residue 

 on the filter. 



9. Ammonia nitrogen. — The ammonia nitrogen in these extracts 

 was determined by the magnesium-oxid method, but the more recent 

 and exact Folin method (6) is recommended. 



10. Nitrogen precipitated by zinc sulphate. — Twenty-five cc. 

 of the original solution were placed in a 50 cc. graduated flask, i cc. 

 of a 50 per cent sulphuric-acid solution was added, with zinc sulphate 

 enough to saturate the solution, after which the flask was filled to the 

 mark with a saturated solution of zinc sulphate. After 18 hours it was 

 filtered and the nitrogen determined by the Gunning method in 20 cc. 

 of the filtrate, corresponding to 10 cc. of the original. The total nitrogen 

 of the extract, less the sum of the coagulable, insoluble, and zinc-sulphate- 

 filtrate nitrogen represents the nitrogen of the zinc-sulphate precipitate. 

 A control determination of the nitrogen of the precipitate was also 

 made. 



11. Nitrogen precipitated by tannic- acid-salt solution. — 

 Twenty cc. of the original solution were placed in a loo-cc. graduated 



