ALBUMIN : THE ISO-ELECTRIC REACTION 35 



[elected above the taps after half an hour, even when no current 

 is applied. This diffusion is more noticeable in concentrated 

 solutions of protein. There is thus a definite tendency for the 

 protein to migrate in both directions, which is affected by an 

 electric field when the protein is charged. The diffusion in 

 one direction is then increased, and in the opposite direction it 

 is decreased. As the iso-electric point is approached, the 

 directive influence of the electric field continually decreases, 

 until conditions finally approximate to those which obtain 

 when no current is passed through the apparatus. The 

 presence of notable quantities of the ions A~ and A+ in approxi- 

 mately equivalent proportions also has an important effect in 

 the region of the iso-electric point, and may possibly cause 

 migration to a slight extent towards both electrodes. 



The products of electrolysis are a frequent source of error 

 when higher concentrations of electrolytes are employed. This 

 disturbing influence can be avoided by the use of unpolarisable 

 electrodes (L. Michaelis), or even in specially favourable cases by 

 preserving a considerable space between the electrodes and the 

 surface of the colloid. A sufficiently large space round the 

 electrodes (Landsteiner and Pauli) and the restriction of the 

 time of passage of the current also decrease the electrolytic 

 effect. Finally, it is necessary, in order to reduce the develop- 

 ment of breaks of potential and secondary electrodes in the 

 liquid, to use as connecting liquids solutions of practically the 

 same conductivity and with ions which differ but little in 

 mobility (Pauli and Flecker *) . Such secondary electrodes are 

 the chief causes of fluctuations in the sign of the charge in the 

 iso-electric zone, in which, naturally, discharge of the colloid 

 most easily takes place. The following table gives some values 

 for hydrion concentrations (C H ) at the iso-electric point deter- 

 mined by electrophoresis. All the results refer to room tem- 

 perature (18). The work on albumin and glutin has been 

 repeated by Pauli and Samec, with identical results. In all 

 cases hydrion regulators, mostly acetic acid acetate mixtures, 

 were used, but for haemoglobin, phosphate mixtures and caco- 

 dylic acid sodium salt buffers were also employed. 

 * Biochem. Zeitsch., 1912, 41, 995. 



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