80 



Miss D. J. Lloyd and Mr. C. Mayes. 



The curve given by equation (3), i.e., J — -j^ooQis §* ves a curve in 



which GH' increases with [H] and only attains a maximum at infinite concen- 

 tration of [H], If we assume an error of 1 in 1000, [H] may be regarded as at 

 infinite concentration when [H] = 01 N. The experimental curve, however, 

 continues to rise very rapidly at still higher concentrations of acid. In his 

 earlier papers Procter considers this difficulty and supposes that a second 

 ionisation constant of a lower value also exists. But equations of the form 



y = — - — H — where a and b are constants, give when plotted for x and y, a 

 x-\-a x + b 



curve which rises rapidly at first and later more slowly, and it proved 

 impossible to fit such a curve to the observations on fig. 4. These seem to 

 indicate a maximum about N' = - 01, then a gradual rise to a possible 

 maximum about W = - 02 followed by yet another increase in N'. The 

 observations for the latter part of the curve, however, are too uncertain to- 

 justify any definite conclusions. 



(b) Calculation of K a . 



If J is the iso-electric point of, an amphoteric electrolyte, K and Kj, its 

 ionisation constants, 



the,, J-^ffe -I.). 



K w at 20° C = 0'86 x 10" 14 , K 4 for gelatine at 20° C = -4-8 x 10~ 12 



J = lO; 4 " 6 (17), 



whence K a should equal 3 - 5 x 10~ 7 . 



Now for a weak acid G (OH) H, we have 



[H']x[G(OHy] 

 [G(OH)H] 



If [G(OH)'J is put equal to v! , and C is put equal to [G(OH)'J + [G(OH)H],. 

 i.e., to the initial concentration of the gelatine, then 



n' _ K a _ K a j- 0H j 



G-n' [H] K K . 



But if 839 is taken as the reacting weight of gelatine, then C = 0'012. 

 hence n' should be less than 0'012. But n' is already greater than - 012 in 

 - 020 N sodium hydroxide and as 1ST increases, %' increases, with an ever- 

 increasing rapidity. Hence C cannot be taken as 0"012, but must be con- 

 siderably greater. That is, the reacting weight in alkaline solution must be 

 less than in acid solution, and hence different linkages must be involved. 



