8 



This was necessary in order to place beyond controversy the fact 

 that colloids could exhibit a proper conductivity that could not be 

 explained away as being due to unknown impurities in accordance 

 with universal custom hitherto. There has since accumulated a mass 

 of corroborative evidence in the measurements carried out by Taylor, ^ 

 Cornish,^ Bowden,* Bunbury,* Martin,* and Laing^^ in collaboration 

 with the writer ; as also the measurements carried out by F. Goldsmidt 

 and his co-workers,^ Weissman' and Kurzman,* and by Reychler,^ and 

 by Arndt and Schiff.^" (See the classified list of references appended.) 



When the results for the potassium and sodium salts of all 

 saturated fatty acids from acetic to behenic acid and likewise the 

 oleates, are reviewed, the utmost regularity is observed in the gradual 

 and regular transition from a typical curve of an electrolyte presented 

 by sodium acetate through the appreciable deviations of the lower 

 fatty acids (hexoates and caprate) to the laurate, in which a step 

 out or maximum and minimum is first observed (in the case of sodium 

 and potassium laurate resi3ectively). 



It must be borne in mind that some of these solutions are extremely 

 viscous whilst others are quite fluid. This enormous alteration in 

 viscosity appears to exert no effect upon the conductivity. Work 

 at present being carried out by Miss Larng in collaboration with the 

 ^vriter shows that when the soap solution has been converted into 

 a solid gel, its conductivity, vapour pressure and concentration of 

 sodium ions are identical with that of the same solution in a state 

 of fluid sol at the same temperature and concentration. This 

 revolutionary observation appears to us to be of great importance 

 for the theory of gels since here the constituent out of which tlie 

 mechanical structure of the gel is built up Ixas to be recognised as 

 constituting one of the best conductors present or the colloidal ionic 

 micelle has to move as freely through the stiff colloidal gel (where 

 structural constituent must then be neutral soap) as through the fluid 

 sol itself. This work and the conclusions to which it leads will be 

 reported upon elsewhere. 



The independence between conductivity and viscosity is further 

 exemplified by the temperature coefiicient of conductivity. In some 

 cases the viscosity is diminished several hundred fold by rise of 

 temperature and yet the temperature coefficient of conductivity is 

 no greater than in others where the viscosity is not so markedly 

 affected. The fact that the temperature coefficient is rather higher 

 than that of an ordinary tyjDical electrolyte is ascribed to hydration 

 and hence increased mobility of the ionic miceUe with rise of 

 temperature. 



FinaU}'- it should be noted that although potassium and sodium 

 soaps exhibit a surprisingly close general resemblance, the typical 

 relationships which have been described are rather more markedly 

 exhibited by the solutions of potassium soaps which evidently 

 contain rather greater quantities of ionic miceUe. 



(b) Osmotic Pressure. 



It is, perhaps, hardly reaUsed how difficult it is to obtain really 

 reliable and unambiguous determinations of the osmotic activities 



