IN ISO-ELECTRIC REACTION 47 



there occurs at the change point in electrophoresis a consider- 

 able combination of acid and consequent formation of electro- 

 positive albumin ions. So that a much larger addition of acid 

 is necessary than the iso-electric reaction found by Sorensen 

 and Michaelis would lead us to expect. The considerations 

 developed by these authors for ampholytes in general, therefore, 

 do not hold for proteins and strong acids. The relatively 

 simple results obtained by the use of hydrion regulators con- 

 taining weak acids exhibit only a particularly favourable 

 limiting case, which varies progressively. 



Any theoretical expression of the reactions of albumin with 

 strong acids in low concentration must accordingly take into 

 account the following facts : 



1. Addition of strong acids to albumin gives a point of 



symmetrical electrophoresis and apparently iso-electric 

 behaviour. 



2. In these mixtures the concentration of hydrion is very 



low, and much smaller than that which obtains at the 

 iso-electric point as found by acetic acid acetate 

 buffer solutions. Thus for i per cent, glutin and 

 albumin it is of the order of io~ 6 . 



3. The negative ion of the acid is abundantly present and free 



in this range of concentration, and there is an excess of 

 electro-positively charged albumin over that which, is 

 negatively charged. 



4. Further addition of acid produces a maximum of neutral 



particles, as shown by maximum precipitation by 

 alcohol and minimum viscosity, the electrophoresis 

 being entirely to the cathode in this region. 



5. The quantity of acid necessary to produce symmetrical 



electrophoresis or maximum of neutral particles in- 

 creases with a rise in the albumin content. 

 A comprehensive view of the complicated relations governing 

 such cases may be gathered from the following considerations. 

 The strong combination of acid with the protein is certainly 

 demonstrated and must be due to development of activity of 

 basic valencies of the protein which do not function in the pre- 

 sence of very weak acids such as exist in acetic acid acetate 



