ALBUMIN : THE ISO-ELECTRIC REACTION 23 



charge when in the natural condition (Landsteiner and Pauli). 

 The same fact was noted a little later and independently by 

 F. Botazzi * and by L. Michaelis. j The latter used Landsteiner 

 and Pauli 's apparatus, and, by employing non-polarisable 

 electrodes, was able to work with colloids to which greater 

 quantities of electrolytes had been added. An anode of silver 

 in potassium chloride, and a cathode of silver in silver nitrate, 

 or of copper in copper sulphate, or similar combinations, are 

 useful for this purpose. It is always important to avoid potential 

 differences at the junctions of the separating liquids by the use 

 of solutions of as nearly as possible the same conductivity. The 

 ions of the electrolytes should not differ greatly in mobility. In 

 the apparatus described above, the short electrodes are situated 

 so far from the surface of the colloidal solution that with o-oi N 

 solutions no disturbances due to electrolysis occur if electrodes 

 of platinum wire are used and the application of the current is 

 not too prolonged. 



As at first albumin particles move slightly to the anode 

 owing to their negative charge, and on addition of increasing 

 quantities of acid become positively charged, it is clear that at a 

 certain acid concentration an indifferent point in the sign of the 

 charge will occur. Under these circumstances albumin shows 

 no electrophoresis in either direction. Hardy called a colloid 

 which showed no potential difference between the particles and 

 the medium an iso-electric colloid. The application of the iso- 

 electric reaction of proteins as an important method of differen- 

 tiating between them has been emphasised in many cases by 

 L. Michaelis, who has also devoted much time with most 

 fruitful results to the theory and practical determination of the 

 iso-electric point. 



The variation in electrical properties of the proteins on 

 addition of acid or alkali is connected with the property they 

 display of behaving as bases towards acids, and as acids towards 

 bases. This property has been well known for a long time, and 

 substances which combined the properties of a weak acid with 

 those of a weak base were called amphoteric electrolytes by 



* A Hi. R. Accad. Lincei, 1908, 17, 49-57. 

 f Biochem. Zeitsch., 1908, 16, 81. 



