A New Method for the Analysis of Proteins. 175 



The remaining 80 cubic centimeters are precipitated with phos- 

 photungstic acid as described by Osborne and Harris, 2 except that 

 twice the volume of solution is employed and the bases are given 

 forty-eight hours to precipitate. It has been found that cystine is 

 precipitated quantitatively with the hexone bases. The phospho- 

 tungstates are washed with suction, and decomposed in the cold 

 with a slight excess of barium hydrate solution. The excess barium 

 is precipitated as carbonate. The solution is then concentrated at a 

 low temperature and brought to 50 cubic centimeters; 10 cubic 

 centimeter samples are taken for total and amino nitrogen deter- 

 minations. The remaining 30 cubic centimeters are washed in a 

 copper Kjeldahl flask with 20 cubic centimeters of water and 15 

 grams of solid reagent sodium hydrate. The mixture is boiled six 

 hours under a reflux condenser, the top of which is closed by a Folin 

 3-bulb tube containing 20 cubic centimeters of N j 10 sulphuric acid. 

 One-half the arginine is split off as ammonia, 3 the reaction being 

 quantitative under the conditions here outlined. 90 to 98 per cent, 

 of the ammonia is caught and titrated in the acid of the Folin tube. 

 The remaining 2 to 10 per cent, is boiled off on a Kjeldahl still, 

 after the alkaline solution has been diluted. The bases, other than 

 arginine, give off no ammonia. To the solution used for arginine 

 determination one adds 3 grams of potassium nitrate, concen- 

 trates, fuses and determines the sulphur, from which the cystine is 

 calculated. By these determinations the phosphotungstate pre- 

 cipitate is divided as follows: 



{Arginine {% of nitrogen, non-amino), deter- 

 mined by decomposing with sodium hydrox- 

 Non-amino N -| ide. 



I Hislidine (% of nitrogen, non-amino) by dif- 

 \ t ference from the arginine. 



(Cystine (all of nitrogen, amino), determined by 



Amino N \ _ suIpl \ ur „ . . f , a'& 



I Lysine (all of nitrogen, amino), by difference 



I L from cystine. 



The amino and non-amino nitrogen in the phosphotungstic 

 filtrate are determined by difference, avoiding the necessity of 

 Kjeldahling solutions containing phosphotungstic acid. The fil- 

 trate is freed from phosphotungstic and sulphuric acids with 



^Jour. of the Amer. Chem. Soc, 1903, xxv, 323. 



3 Osborne, Leavenworth, and Brautlecht, American Jour, of Physiol., 1908, xxiii, 



180. 



Phosphotungstate 

 precipitate 



