14 



twelve hours and then filtered, after which the precipitate was thor- 

 oughly washed with a saturated solution of zinc sulphate, slig-htl}^ acid- 

 ified with sulphuric acid. The nitrogen in the precipitate was then 

 determined. 



Determ,inatio7i of nitrogen jyrecvpitated hy tannin and sodium chlo- 

 rid. — Measured portions of 200 cubic centimeters each of the cold-water 

 extract were transferred to 250 cu})ic centimeter measuring- fiasks 

 and 1 g-ram of pure sodium chlorid and 5 cubic centimeters of a solu- 

 tion containing 12 per cent of tannin were added. The solution was 

 then diluted to 250 cubic centimeters, allowed to stand twelve hours, 

 filtered through a dry filter, and the nitrogen determined in a measured 

 volume (200 cubic centimeters) of the filtrate. 



Determination of nitrogen precipitated hy phospJiotungstie acid from 

 a cold solution. — Measured amounts of 200 cubic centimeters each of 

 the cold-water»extract were transferred to 250 cubic centimeter meas- 

 uring flasks, with 5 cubic centimeters of 50 per cent sulphuric acid 

 and 10 cubic centimeters of phosphotungstic acid solution (prepared 

 as directed by Wile}^)." The solution was then diluted to 250 cubic 

 centimeters, allowed to stand twelve hours, filtered through a dry filter, 

 and the nitrogen determined in 200 cubic centimeters of the filtrate. 



Determination (f nitrogen precip>itated hy jyhosjyhotungstic acid from 

 a hot solution. — Measured portions of 200 cubic centimeters each of 

 the cold-w^ater extract were treated with 5 cubic centimeters of 50 per 

 cent sulphuric acid and then heated to rapid boiling. A slight excess 

 (10 to 15 cubic centimeters) of phosphotungstic acid solution was added 

 and after boiling gently for five minutes the hot solution was filtered. 

 The precipitate was washed thoroughly with boiling water and then 

 the nitrogen which it contained was determined. 



Determination of nitrogen precipitated hy Stutzer's reagent. — jNleas- 

 ured amounts of 200 cubic centimeters of the cold-water extract each 

 were placed in 250 cubic centimeter measuring flasks and 3 cubic cen- 

 timeters of Stutzer's reagent was added. The solution was then 

 dilmted to 250 cubic centimeters, thoroughly mixed, allowed to stand 

 twelve hours, filtered through a dry filter, and the nitrogen determined 

 in measured portions (200 cubic centimeters) of the filtrate. 



Determ ination of nitrogen as ammonia. — Portions of 200 cubic cen- 

 timeters each of the cold-water extract were distilled with magnesium 

 oxid in the form of milk of magnesia and the ammonia thus liberated 

 was determined in the usual way. 



Determination of nitrogen compounds precipitated directly l>y 

 Srfwi^Vi.*'— Portions of 200 cubic centimeters each of the cold-water 

 extract were transferred to Kjeldahl digestion flasks, acidified with 2 



« Principles of Agricultural Analysis, vol. 3, p. 454. 



& This determination has recently been discontinued, as bromin has been proved to 

 be an unreliable precipitant for proteids. 



