POTENTIAL DIFFERENCES AND COAGULATION 



O F C O L L O D I O N P A R T I C L E S I N 



A O U E O U S S U S P E N S 1 O N S 



J A C O U E S LOE B 



From the Laborntorics of the Kockcíellcr Institutc for ^[cdical Research 



The precipitation and coagulation of suspended colloidal partióles 

 play a great role ¡n the fixation of histological preparations and they play 

 probably also a great role in the formation oí membranes and other solid 

 structures of the cells. It is therefore justifiable that in the jubilee volu- 

 me to be oft'ered to Professor Ramón y Cajal a contribution to the theory 

 of the process of precipitation of colloidal suspensions should be inclu- 

 ded. Jevons was probably the first to express the view that electrical 

 charges prevent suspended colloidal partióles from settling, and this view 

 was put on a solid basis when Hardy proved that the stabiiity of a sus- 

 pensión became a minimum when the partióles no longer migrated in a 

 galvanic field. It is well known that salts have a precipitating action on 

 colloids in suspensión, and that there is a wide difference in the molecu- 

 lar concentration at which the diíTerent salts precipítate a colloidal sus- 

 pensión. Schulze, Picton and Linder, and Hardy found that that ion of 

 a salt is elTective in precipitation which has the opposite sign of charge 

 to tliat of the colloidal partióle, since the precipitating efficiency of the 

 salt increases with the valenoy of that ion i. Powis - has made it proba- 

 ble that the stabiiity of oil emulsions in water is destroyed when the po- 

 tential diíTerence between oil droplets and water reaches a oertain oriti- 

 oal valué of about 30 niillivolts. According to his results, the difference 



' The literature on this subject can be found in Burton, E. F.: Tlie Physical 

 Properties of Colloidal Solutions, 2nd ed., London, New York, Bombay, Calcutta, 

 and Madras, 1921. 



' Powis, F.: Z. physik. Chem., 1915, i.xxxix, 186. 



