220 CHEMISTRY OF THE PROTEIDS CHAP. 



subtraction, of an oxygen-atom without changes in the constitution of 

 the compounds. The theory of pseudo-acids is further discussed by 

 Zawidzki in a later paper, 1 and the substitution of carbon-remainders 

 for hydroxyl-groups in pseudo-bases by Martin Freund. 2 



Hydrolytic dissociation must always be taken into account under 

 the following conditions : 



1. Between the water, the acids or bases, and the albumins a state 

 of equilibrium exists for any given concentration, and this equilibrium 

 is altered whenever one of the factors is changed. For this reason it 

 is impossible to determine by titration the acidity or basicity of an 

 albumin solution. Each cubic centimetre of NaOH solution added to 

 a solution of an albumin-chloride diminishes the excess of hydrochloric 

 acid, and thereby leads to an increase of hydrolytic dissociation, till 

 ultimately nearly the whole of the hydrochloric acid is split off from 

 the albumin and is thereby rendered free. Titration amounts, 

 therefore, simply to an estimation of the whole of the acid with which 

 the albumin was united, and the result obtained is the same as if the 

 albumin had not been present at all. This method of titration is made 

 use of in determining the acidity of gastric contents, in which albumin 

 and albumose chlorides are present in addition to free hydrochloric acid. 

 When titrating with rosolic acid or with phenolphthalein, the albumin 

 chlorides are estimated as well as the free hydrochloric acid, and 

 therefore one speaks of * the total acidity.' As the state of equilibrium 

 between albumin, salts, and water, is changed every time a substance 

 is added, one ought never to use kinetic methods for determining the 

 basicity of albumins, i.e. methods which depend on the removal or the 

 using up of one of the components. This was pointed out by 

 v. Rhorer. To overcome this difficulty Sjoqvist and Bugarszky arid 

 Liebermann determined the basicity of albumins by determining the 

 electrical conductivity of albumin-chlorides, while Cohnheim estimated 

 the free hydrochloric acid by its sugar - inverting power. Both 

 methods are very complicated, and it has been shown that results of 

 sufficient accuracy can usually be obtained by other methods. Cohn- 

 heim and Spiro and Pemsel have salted out the albumin-chlorides, 

 which is quite as easy as salting out the albumins themselves, and 

 have then determined in the filtrate the free hydrochloric acid. Still 

 simpler is the method of Cohnheim and 'Krieger, 3 who precipitate the 



1 Zawidzki, Ber. d. deutsch. diem. Ges. 37. 2298 (1904). 



2 Martin Freund, ibid. 37. 4666 (1904). 



3 0. Cohnheim and H. Krieger, Zeitschr. f. Biol. 40. 95 (1900) ; Miincfiener 

 medizin. Wochenschr. 1900, p. 381. 



