Il6 



Scientific Proceedings (74). 



owing to the fact that the OH ion is more readily adsorbed than 

 the Na ion. NaCl exerts a similar effect to NaOH, the CI ions 

 exerting a dispersing effect analogous to that of the OH ions, but 

 since they are far less readily adsorbed than the OH ions their 

 effect is considerably smaller. This point may be demonstrated 

 by adding NaCl in increasing amounts to a soap solution contain- 

 ing enough alkali to give a strong pink color with phenolphthalein. 

 A discharge of the color takes place, and the amount of alkali re- 

 quired to compensate for the effect of the NaCl introduced follows 

 a logarithmic curve indicating clearly that the added NaCl either 

 promotes the adsorption of OH ions already present, or that the 

 CI ions are more readily adsorbed than the Na ions, thus leading 

 to a reduction in the OH ion concentration in the water phase. 



The soap particles possess a negative charge attributable pre- 

 sumably to adsorbed anions. This charge prevents their coales- 

 cence until the concentration of the Na ions reaches such a point 

 that they also come into play and by adsorption on the particles 

 tend to counteract or diminish the negative charge conveyed by 

 the previously adsorbed OH or CI ions. 



When a certain concentration of the cation is reached, a criti- 

 cal zone commences, in which jelly formation or precipitation 

 appears to depend entirely upon the relative proportions of ad- 

 sorbed cations and anions. If at the commencement of this critical 

 zone the residual negative charge carried by the particles resulting 

 from an adsorption of anions in excess of cations is sufficient to 

 maintain a perfect dispersion of the particles throughout the 

 system, as indicated by an examination of the suspensions for 

 Brownian movement by means of the ultramicroscope, jelly 

 formation will ensue at higher concentrations. If this residual 

 negative charge on the particles is insufficient, if they no longer 

 exhibit perfect dispersion when examined by means of the ultra- 

 microscope, if agglutination, aggregation and sedimentation under 

 the influence of gravity has already commenced, precipitation 

 necessarily ensues at higher concentrations. It is obvious, there- 

 fore, that the formation or non-formation of the jelly in this 

 critical zone is dependent simply upon the relative concentration 

 in the system at the lower critical point of anions like OH, which 

 are more readily adsorbed and anions like CI which are less readily 



