14 



Electrolytes Avith the common alkali ion must exert three chief 

 effects upon a colloidal electrolyte. First the furthering of formation 

 of ionic micelle if large quantities of simple ions are still present; 

 secondly, driving back the dissociation with its corresponding altera- 

 tion in the composition of the ionic micelle; and third, diminishing 

 hydration of the ionic micelle. 



The only mixtures which have been properly investigated are 

 those of potassium laurate and potassium oleate. Addition of small 

 quantities of potassium laurate to potassium oleate slightly increase 

 the viscosity at 90°, whilst at 20°, the viscosity is greatly diminished, 

 thus very much lowering the temperature coefficient. Such an addition 

 must have partly the same effect of that of an electrolj^e with the 

 added complication of the possible formation of mixed ionic micelle. 

 A mixture of equal quantities of potassium laurate and potassium 

 oleate fairly closely resembles the pure laurate. A mixture of even 

 relatively small amounts of laurate with the oleate causes the solution 

 to respond to the addition of salts in a manner much more closely 

 resembling the laurate than the original oleate. 



An addition of equivalent quantities of various electrolytes the 

 hydroxide has the greatest effect, followed by the chloride, and then 

 the carbonate. Although if equimolar concentrations of carbonate 

 and hydroxide are taken, the order of magnitude of the effects are 

 the same. 



It should be emphasised that other colloidal electrolytes exhibit 

 the same typical behaviour in the addition of electrolytes as has 

 been observed, for example, by Woudstra in the case of ferric 

 hydroxide (chloride). According to Pauli this also is a case of a 

 colloidal electrolyte. 



An excellent example of an industrial appHcation of this behaviour 

 in the closely analogous case of sodium silicate is to be found in the 

 use by Malcolmson {Jour. Ind. and Eng. Chem., 1920, 12, 174) of 

 brine for diluting water glass whilst retaining its adhesive power. 

 In this way a given volume of water glass could be increased by 

 25 per cent, without reducing its viscosity. 



(b) Density. 



Soap solutions are remarkable for their bulkiness. All soap 

 solutions have approximately the same density as water of the tempera- 

 ture, and this even in extreme concentration. For example, the 

 volume of a normal solution of sodium stearate is 31 per cent, greater 

 than that of a solution of sodium acetate containing the same amount 

 of water. Not only so, but we have here the almost unique case 

 of the solution being in some cases less dense than either constituent.* 

 For instance, a normal solution of sodium palmitate has a density 

 equal to 0-997 of that of water of the same temperature (at 90°). 



The potassium soap solutions are slightly denser than those of 

 sodium. The ammonium soaps are somewhat Ughter than the 

 sodium soaps. The highest homologues of the fatty acids produce 

 soap solutions of the least density. There is a steady increase as 



* Compare the case of p. nitrotoluene in carbon bisulphide ; Hyde, Joum. 

 Amer, Chetn. Soc, 1912, 34, 1507. 



