vi THE HYDROLYSIS OF ALBUMINS 221 



chlorides of albumins by means of the neutral alkaloidal-precipitants, 

 and then determine the hydrochloric acid in the filtrate. The reaction 

 occurs according to the equation : 



Calcium-phosphotungstate + album in-hydrochloride = 

 Albumin-phosphotungstate + calcium- chloride. 



The insoluble albumin-phosphotungstate is precipitated, and the 

 filtrate may then be titrated without fear of hydrolytic dissociation. By 

 means of this method Erb determined his figures. The same method 

 may also be used for the albumoses of the gastric contents. 1 



A still simpler method is one which has been used for years for 

 clinical purposes, namely, the titration of the albumin-chlorides by 

 means of certain indicators 'for free hydrochloric acid,' such as 

 phloroglucin vanillin, tropaeolin, Congo-red, methyl-violet, etc. Of 

 these Giinzburg's reagent (phloroglucin vanillin) and tropaeolin give,, 

 according to Cohnheim and Cohnheim and Krieger, approximately 

 correct values. 



The power albumins possess of combining with bases has been 

 determined by Bugarszky and Liebermann, who measured the electrical 

 conductivity, and by Spiro and Pemsel, who employed the salting-out 

 method. 



2. The alkaloidal reagents form with albumins insoluble salts, 

 but these salts readily undergo hydrolysis and remain in solution if 

 free acid be not present. Such weak bases as the albumins require, 

 therefore, a certain excess of acid, e.g. phosphotungstic acid, to become 

 precipitated. Neutral phosphotungstates, picrates, tannates, iodine, 

 potassium iodide, biniodide of mercury in potassium iodide, potassium 

 ferrocyanide, do not precipitate albumin they only do so if the 

 reaction be acid. The reagents generally used are therefore bin-iodide 

 of mercury in potassium iodide + hydrochloric acid ; potassium ferro- 

 cyanide + acetic acid ; picric acid ; tannic acid ; and phosphotungstic 

 acid. v. Rhorer also states that feeble acids, such as acetic or lactic 

 acid, cannot take the place of hydrochloric acid. Only the histones^ 

 are sufficiently strong bases to be precipitated if the reaction be 

 neutral, while the still more strongly basic protamins are precipi- 

 tated if the reaction be even alkaline, and in this respect the protamins 

 resemble the alkaloids. The bases contained in albumin are like- 

 wise only completely precipitated by phosphotungstic and sulphuric 

 acids. After precipitates have once been formed, they will remain 

 permanent only if there be a certain excess of acid, for which reason 



1 0. Cohnheim and H. Krieger, Zeitschr. f. BioL 40. 95 (1900) ; MuncJiener 

 medizin. Woclienschr. 1900, p. 381. 



