240 ALBUMINOIDS. 



Precipitation by phenol and calculation from the nitrogen 

 contained in the precipitate has been recommended by Church i for 

 the estimation of the albuminoids in vegetable infusions, in the 

 presence of amides, etc. 



My experience in precipitating albumen, etc., with phenol 

 compels me to xioubt the possibility of always obtaining complete 

 separation by this means. Sestini has also expressed himself to 

 the same effect. 



§ 233. Extraction with Dilute Add, — It has already been observed 

 that the residue of a vegetable substance, after exhaustion with 

 water, yields albuminous substances to dilute alkali. The same is 

 the case with dilute acid (2 "12 per cent. HCl), the substances 

 extracted being gluten, fibrin (§ 235), gliadjn; mucedin, etc. But 

 the albuminoids brought into solution by these two solvents do 

 not appear to be always ide^itical ; at least Wagner found that 

 the amount removed by dilute alkali (after exhaustion of the 

 material with water) did not coincide with that extracted by acid. 

 (Compare also ^111, 106). It might nevertheless in many 

 cases be desirable to ascertain to what extent the substances allied 

 to albumen resist the action of water, dilute alkali (cf. § ^26) and 

 dilute acid respectively. , 



In estimating the value of certain vegetable substances as foodsj 

 it will often be found desirable to determine what proportion of 

 proteids are dissolved by the combined action of pepsin and 

 hydrochloric, acid after the material has been exhausted with water. 



From experiments that have been made in this direction it 

 would appear that hydrochloric acid and pepsin dissolve more than 

 the former alone. ^ In making such estimations I should recommend 

 100 cc. of water, 1 gram of 33 per cent, hydrochloric acid, and 0-1 



by phosphotungstic acid. The precipitate is filtered 8ff as rapidly as possible, 

 washed with 5 per cent, sulphuric acid and transferred whilst still moist to a 

 mortar. It is then triturated with excess of hydrate of baryta, warmed for 

 a short time and filtered. If the filtrate is colourless, the biuret-test can be 

 applied ; if yellow, it can frequently be decolourized by adding a little acetate 

 of lead, and filtering off from the precipitate thus produced. A.nimal charcoal 

 should not be used, as it absorbs peptone. Schnlze and Barbieri, who pro- 

 posed the foregoing method, have obtained approximate quantitative results 

 colorimetrically. 



' Landvrirthsch. Versuchsst. xxvi. 193 (Journ, Chem. Soc. xxxviii. 588). 

 See also Sestini, Joe. cit. 



" See Kessler, Versuche iiber die Wirkujig des Pepsms auf einige animal 

 u. vegetab. NahrungsmitteL Piss. Dorpat, 1880. 



