CONDUCTIVITY OF COLLOIDAL MIXTURES 



307 



described above. The three different classes of material gave 

 practically the same kind of resistance curves. There was 

 greater variation in the case of colloid III, doubtless because of 

 the presence in it of the whole wheat flour with its undetermined 

 electrolytes. In the following curves, which are typical, the 

 points just made are well illustrated. The rate of penetration 

 of the ions is at first very rapid, the resistance often falling 1500 



Fig. 1 



ohms in the first minute, then it gradually slows dowTi and the 

 final fall of 50 to 100 ohms is only accomplished after some 

 forty hours. 



During the first few hours there is an average difference of 

 20% between the readings with NaCl and CaCl2 as in figure 1. 

 The diffusion of Na ions is faster than the diffusion of the Ca 

 ions because of the greater adsorption of the latter by the gela- 

 tine. This adsorption occurs first at the surface of the colloid 



