IN ISO-ELECTRIC REACTION 



49 



3. The ions formed from pure albumin and weak acids and 

 bases can be considered monovalent in contra-distinc- 

 tion to those of the protein salts. 



The addition of strong acids to albumin gives rise to four 

 different effects in the solution which are shown by the points 

 a, b, c, d (Fig. 7). In illustration of these we shall adopt the 

 scheme previously employed, and, to simplify notation, choose 

 the reaction with hydro- 

 chloric acid as an example. 



a. The first point which 

 is reached when acid is 

 gradually added is due to the 

 reaction of A+OH with HC1 



and a slight repression of 

 the ionisation of A~H, so 

 that hydrions and chlorions 

 are present in equal num- 

 bers, as also are the charges 

 on the negative and positive 

 albumin.* This is a true 

 iso-electric point which, how- 

 ever, can only be found by 

 an electrometric determina- 

 \ tion of [H-] and [Cl']. It 

 occurs at such a low con- 

 centration of acid that 

 the small concentration of 

 chlorions cannot be measured, 

 protein migrates to the anode. 



b. As more acid is added a further point is reached, when the 

 albumin changes its direction of migration and moves towards 

 the cathode instead of towards the anode. This change point 

 in electrophoresis is only apparently iso-electric, as proved by 

 electrometric measurements, which show an excess of negative 

 Cr ions over the positive H- ions, the latter having a concen- 



Cl 



FIG. 7. 



a, true iso-electric point; 



b, point of iso-molar migration. 



c, the maximum of neutral particles. 



d, maximum combination with acid. 



Under these conditions the 



tration of 2 X io~ 6 the former 



* The 



i COH 



OH' 



ions which are present 

 are here omitted. 



of 07 i-o x 10 



according to 



One is 

 the equation 



