DISTRIBUTION OF NITROGEN 



101 



mixture of equal parts of amyl alcohol and ether. Complete solution 

 of the precipitate occurs after shaking for one or two minutes. Should 

 an oil appear at the bottom more of the amyl alcohol-ether mixture is 

 added until the whole of it floats upon the surface. 



If the layers do not separate readily with a clear boundary between 

 them, due to humin not having been completely absorbed by the 

 calcium hydrate previously arid to its precipitation 

 by phosphotungstic acid, the whole solution 

 without separation of the layers is passed 

 through a Buchner funnel with suction. The 

 clear filtrate readily separates into two layers. 

 The aqueous portion is extracted with three 

 successive portions of amyl alcohol-ether using 

 a volume of mixture equal to one quarter of the 

 aqueous solution. The combined amyl alcohol- 

 ether extracts are shaken once with water, and 

 this portion of water, after being shaken once 

 or twice with fresh amyl alcohol-ether, is added 

 to the aqueous solution. This contains the bases 

 and should be free from phosphotungstic acid 

 as shown by testing a few drops with baryta 

 solution ; a precipitate should not be formed. 

 The solution is evaporated to dryness in vacuo 

 to drive off the excess of hydrochloric acid and 

 the residue dissolved and diluted to 50 c.c. 



This procedure is more rapid than the older 

 and has the advantage that no barium is present, 

 which may cause bumping in estimating the 

 arginine. 



7. Estimation of Arginine. Arginine is 

 stated by Van Slyke [1911, 4] to be quantita- 

 tively decomposed by boiling with 50 per cent, 

 alkali with the loss of half of its nitrogen. Its estimation is performed 

 before that of the total nitrogen contained in the solution. 



25 c.c. of the solution are placed in the 200 c.c. flask of the 

 apparatus shown in fig. 6. 



The Folin bulbs are connected to the flask either by a ground 

 glass joint, or by a heavy piece of rubber tubing. These bulbs con- 

 tain 15 c.c. of decinormal acid, coloured with alizarin sulphonate. 

 1 2 '5 grams of solid potash and a piece of porous porcelain are added 



FIG. 6. 



From Journ. Biol. 

 Chem., 1911, 10, 26. 



