22 ELECTRIC CHARGE ON NATURAL SOLUBLE 



I I 



until it is full to a level just above the two open taps. These 

 are then closed, avoiding the inclusion of air bubbles. The rest 

 of the apparatus, after cleaning, is then filled with a liquid of the 

 same conductivity, e.g., a solution of KC1 or similar salt which 

 is in equilibrium with the colloidal solution. This liquid is 

 levelled by opening tap III., which is then closed, and I. and II. 

 opened. The liquid lying above the colloid must be less dense 



than the colloid, and a 

 clean line of division is thus 

 obtained. When the cur- 

 rent is switched on, negative 

 colloids rise up through I., 

 positive colloids through 

 II. With a neutral sol no 

 movement on either side 

 occurs. At the end of the 

 elec.trophoresis taps I. and 

 II. are closed and the con- 

 tents of the parts of the 

 U-tube above the taps 

 removed by a fine pipette 

 and tested. The apparatus 

 can also be used as a null 

 instrument, for instance, to 

 find the point when no 

 migration of the albumin 

 occurs, for which purpose 

 filling with trichloracetic 

 acid gives a high degree of 

 sensitiveness (Wo. Pauli and Samec). L. Michaelis introduces 

 crystals of sulphosalicylic acid for the same purpose. This 

 apparatus can further be used for the direct measurement 

 of the rate of motion of charged colloid particles in the 

 electric field, provided the distance which the boundary line 

 moves in a given time is determined with a known potential 

 gradient. 



By the use of this apparatus, it can be shown that proteins, 

 such as albumin and glutin, regularly show an electro-negative 



FIG. 3. Improved electrophoresis 

 apparatus. 



