THE COLLOID-CHEMISTRY OF SOAPS 109 



becomes " less colloid," approximates more nearly a " true " 

 solution, and hence its viscosity can only fall. 



The same general effect of the ammonium radical is still appar- 

 ent when instead of ammonium hydroxid some salt like ammonium 

 chlorid is added to potassium oleate (see Fig. 71 and Table L). 

 Here again no initial increase in viscosity is to be observed. Since, 

 however, ammonium chlorid is the salt of a weak base with a 

 stronger acid the secondary effect of an overplus of acid formed 

 through hydrolysis also appears. By means of this acid, fatty 

 acid is liberated from the soap and then remains emulsified in 

 the soap. A third effect is exerted in this illustration by the 

 unchanged ammonium chlorid and the newly formed potassium 

 chlorid which exert a dehydrating effect (see below) upon both 

 < >f t he soaps. 



These ideas may be further verified by using ammonium 

 acetate. There is still no perceptible initial increase in viscosity, 

 and since the salt used is more nearly neutral, fatty acid is not 

 set free. In the higher concentrations of this salt the soap merely 

 separates out in the usual fashion. 



(2) A soap is formed less soluble in, and a poorer solvent for, the 

 dispersion medium. This is observed when magnesium, calcium. 

 iron or copper salts are added to a solution of potassium or 

 sodium) oleate. Under these circumstances, too, the systems 

 as a whole again become more liquid, though it is not in this 

 instance 1- lie soaps formed are more soluble in the solvent 

 or more hydratable but because they are less soluble and less 

 hydratable and so fall out, allowing the viscosity of the pun* 

 solvent (essentially salt water) to come to the front. In con- 

 trast to the systems described under (1), these regularly become 

 milky or white while the former become more transparent i unless 

 some secondary change like the liberation of fatty acid in einulsi- 



fonn >uper\enes). 



(3) The change in kind of soap is negligible or there is none at 

 nil. This happens, for example, when potassium hydmxid or 



MM! potassium salt is added to a potassium soap. Cndcr 

 these circumstances, with increasing concent ration of the added 

 substances, all the changes doscril>ed in the above experiments 

 are Seen to Occur. There i<. first. ;m increase in viscosity \\hich. 



nt i- no! too great, results in gelation, 

 followed by a secondary liquefaction resulting ultimately m mm- 



