The Titration Curve of Gelatine. 



75 



from Blasel and Matula's formula it is assumed that the gelatine hydro- 

 chloride contributes no chlorine ions to the system ; in those for W it is 

 assumed that the gelatine hydrochloride contributes all its chlorine as free 



0'05 



0-02 - 



OO/ - 



Fig. 4 



x = Experiment/ Points. 



o = Po/r?rs ro/re/i fro/?? sm oof red 

 cure? /r? F/G.2. 



[H] 



J I I L. 



O 005 O-ZO 0-/5 



Curve of acid fixed. Abscissa; = [H]. Ordinates = Acid fixed or N'. 



chlorine ions to the system. The two curves, n : [H] and jST : [H], there- 

 fore form the limits within which the actual curve must lie. In hydrochloric 

 acid of concentrations less than 0'02 grm. of free hydrogen ion per litre the 

 difference between the two limiting curves is negligible.] It can be seen 

 that the curve is not a simple smooth curve, but that it consists of two, and 

 possibly three, distinct regions. The deductions from this will be considered 

 after the gelatine-sodium hydroxide curves have been described. 



(b) The Gelatine — Sodium Hydroxide System. 

 Let N represent the normality of the caustic soda and « its degree of 

 ionisation at 20° C, then — log 1ST « equals the hydroxyl ion concentration of 

 the system and 1443 — ( — log 1ST «) is the hydrogen ion concentration. 

 Values for « are given by Kohlrausch (9), Xoyes (18) and Jones (6). 

 Unfortunately they differ considerably. The values given by Noyes were 

 taken to plot the (broken) curve 14-13 +log N « in fig. 3 (marked C in the 

 margin). Noyes' values only go to a concentration - 05 1ST. The curve was 

 extended beyond this region by taking Jones's figures for « and adding to 

 them the difference between his figures and Xoyes', which may be taken as 

 0'05 if a. is expressed as fractions of unity. X, a and 14 - 13 + log X cc are 

 shown in the first three columns of Table II. The fourth column gives 

 the readings obtained for E, the electro-motive force at the surface of the 

 hydrogen electrode in a 1*00 per cent, solution of gelatine. The fifth column, 



