II 



NITROGEN RADICALS 79 



precipitate was allowed to stand for twenty-four hours before it was 

 mixed with the diluting fluid, because during this time the originally 

 flocculent precipitate becomes crystalline. The phosphotungstate 

 precipitate of arginin, of 0*00118 grm. ( = 0*00038 grm. nitrogen), 

 passes into solution only after 26-30 ccm. of phosphotungstic acid 

 have been added, i.e. after a dilution of 1 : 22,000 to 1 : 25,000. In 

 Hausmann's process, in estimating the nitrogen of 1 grm. of albumin, 

 the volume of fluid dealt with amounts to 80 ccm., and in this quantity 

 there will remain in solution 0'0035 arginin ( = 0*001 grm. nitrogen), 

 which, if we take the arginin-content of the albumin-molecule to equal 

 10-20 per cent, amounts to a loss of 1-8 to 3 '5 per cent. If the 

 precipitate be washed for a long time, the loss may amount to 10 

 per cent. 



Lysin behaves quite analogously to arginin. 



Histidin reacts, however, quite differently. It is readily pre- 

 cipitable by phosphotungstic acid, but redissolves if there be a trace of 

 excess of phosphotungstic acid, provided the solution is concentrated. 

 If, however, the solution of phosphotungstic acid is very dilute, then 

 an excess of the acid does not dissolve the histidin-phosphotungstate 

 precipitate. Therefore have 1 part of the diamino-nitrogen to 1000- 

 1500 ccm. of solution. If the histidin has not been completely pre- 

 cipitated, then a precipitate will be found on diluting the filtrate or 

 on adding some more dilute phosphotungstic acid. 



If the rules laid down above are followed out, the error in the 

 estimation of the total di-amirio-nitrogen will amount to 5-10 per cent, 

 i.e. instead of 4 per cent di-amino-nitrogen only 3*6-3*8 per cent will 

 be obtained. 



Sub. 2. Kutscher's objection to Hausmann's method, on the ground 

 that mono-amino-acids are also precipitated by phosphotungstic acid if 

 they are in very concentrated solutions and in the presence of very 

 strong acid (Stolte 1 ), is well known; but mono-amino-acids in 0*5 per 

 cent strengths are not precipitated, and inasmuch as this percentage is 

 not exceeded if Hausmann's directions as to dilution to 70-80 ccm. are 

 followed out, Kutscher's objections to the method are groundless. 



Phenylalanin and cystin must also be taken into consideration, 

 especially since Schulze and Winterstein 2 have recommended phospho- 

 tungstic acid for the separation of these amino-acids. Gumbel points 

 out, however, that according to Winterstein 0*1 grm. of phenylalanin 

 in 50 ccm. of water is no longer precipitated by phosphotungstic acid, 



1 Stolte, Hofmeisters Beitrdge, 5. 19 (1904). 



2 Schulze and Winterstein, Zeitschr. f. physiol. Chem. 29. 155 (1901), and 33. 

 374 (1902). 



