CONDUCTIVITY OF COLLOIDAL MIXTURES 315 



for temperature. The difference between the resistance of any 

 tube and its control represented the resistance due to the gelatine 

 alone. This was of course a negative quantity in the case of 

 pure gelatine and its control, but for all salt concentrations 

 above 0.005 M NaOH it was positive. This is to be expected 

 since the colloidal particles obstruct the path of the ions; and 

 the effect is overbalanced by the native gelatine ions only when 

 the added salt concentration is very low. 



Since the purpose in performing these experiments was merely 

 to demonstrate the connection between precipitabihty and con- 

 ductivity, only the most elementary of Fenn's combinations 

 were attempted. NaCl in concentrations from to 1.0 M were 

 added to the pure gelatine solution and to gelatine solution plus 

 NaOH. CaCL was also added at similar concentrations and 

 curves plotted for the specific resistances due to the gelatine. 

 Sample curves are shown herewith. It will be noted that the 

 curves in which the NaOH is lacking exhibit the character which 

 has been previously pointed out, i.e., that until the higher salt 

 concentrations are reached the resistance values for the gelatine 

 are negative. This lack of resistance is due to native electro- 

 lytes in the gelatine which provide enough ions to overbalance 

 the inhibitive effect of the colloidal particles. When the curves 

 are examined with this fact understood, they are seen to agree 

 with Fenn's hypothesis, for the resistance of the gelatine does 

 decrease as the salt concentration increases. 



The curves of the resistance offered by gelatine plus NaOH 

 are remarkably similar to Fenn's curves of precipitabihty. The 

 isoelectric point where the resistance is greatest, occurs when 

 the ratio of CaClo to NaOH is 0.0125 M: 0.005 M. In the case 

 of NaCl the isoelectric point occurs before the concentration 

 reaches 0.00625 M and since this is the lowest concentration used, 

 the curve of resistance falls from the start, as did Fenn's curve 

 of precipitabihty. 



It is possible then to make the assumption that in the case of 

 protoplasm electrical conductivity and hence permeability is 

 determined by the presence of a precipitate, which in turn is 

 dependent as to its quantity upon the relative proportions of 



