246 Biological Chemistry. 



In estimating the relative amounts of the three diamino- 

 acids they are separated as phosphotungstates, nearly in the 

 same way as in the process for the determination of the 

 Haussmann numbers. In fact, the latter are determined 

 by employment of the same sample of material used for 

 the estimation of the individual diamino-acids. The 

 diamino-acids are set free from the phosphotungstates by 

 means of baryta. In an aliquot portion of the liquid the 

 total nitrogen is determined (diamino-acid nitrogen), in 

 another portion the ammo-nitrogen which reacts with 

 nitrous acid, and in a third portion the arginine is esti- 

 mated by determining the amount of ammonia evolved 

 when the liquid is treated with potassium hydroxide under 

 certain standard conditions. The relative amounts of 

 arginine, histidine, and lysine can then be readily calcu- 

 lated from the data given above. The crux of this valuable 

 method, which is due to Donald van Slyke, lies in the 

 invention of an apparatus for the estimation of the nitrogen 

 evolved when the solutions of the substances containing an 

 amino group are treated with nitrous acid. This is de- 

 vised in such a way that nitrous acid is first generated in 

 a vessel by treatment of sodium nitrate with glacial 

 acetic acid, which is shaken until all the air is driven out. 

 A solution of the substance under examination is then run 

 in, and the mixture is well shaken with the excess of 

 nitrous acid in the flask. Nitrogen, mixed with nitric 

 oxide, is evolved, and is collected in a gas burette. The 

 mixture of gases is then passed through " Hempel " bulbs 

 containing an alkaline solution of potassium permanganate, 

 which absorbs the nitric oxide, and the gas is then with- 

 drawn back again into the burette, and the volume of the 

 nitrogen is noted.* 



* This apparatus has been largely employed lately in investigations on 

 proteins and their digestion products. It is described in the Berichte der 

 deutschcn chemischen Gesellschaft, 1910, 43, 3170, and also in (in English) Allen's 



