Electromotive force measurements were made with sodium-respopsive glass electrodes and saturated KCl, calomel electrodes on mixtures of sodium alkyl sulfates. Two solution pairs were studied: sodium decyl and dodecyl sulfates and sodium dodecyl and tetradecyl sulfates. Critical micelle concentrations were selected from plots of p y a us. log c. The procedure of Mysels and Otter was used to establish the non-micellar concentrations in the micellar solutions of mixtures. The extent of the dissociation of sodium counterions by the micelles was estimated from the reduced data. From the activity coefficients strong interaction below the critical micelle concentration was inferred for all the mixtures except those containing more than 25 mole Y, c f sodium decyl sulfate.The present investigation examines the behavior of aqueous solutions of mixed colloidal electrolytes by means of electromotive force (e.m.f.) measurements based on a sodium-responsive glass electrode. Botr6, Crescenzi, and Mebe' carried out similar measurements for solutions of a few single colloidal electrolytes by using cationic organic membranes. In their discussion they treated the micelles as polyelectrolytes.It often is convenient to treat micellar solutions of colloidal electrolytes as a system of quasi-phases, one, an aqueous or non-micellar medium, within which a second, the micelles, is distributed. Lange2 recognized that in a micellar system, which contains two surface active Eiolutes, the critical micelle concentration (c.m.c.) varies with the relative amounts of the two solutes and that the locus of the c.m.c. was a kind of phase boundary of the aqueous medium. On the basis of a theoretical model, Mysels and Otter3 recently employed conductivity measurements to obtain the boundary of the mixed micelles and the tie lines to the aqueous medium; they discussed also the thermodynamics of the system.
Summary
Relative protection of various compounds against calcium salts was determined by a pour‐foam test, using sodium cetyl sulfate as a foam‐producing indicator. The sensitivity of the test corresponds to less than 2 p.p.m. of calcium salt.
Some of the data are compared with similar tests, using sodium oleate as an indicator, and advantages of the cetyl sulfate test are noted.
The test is discussed from the point of view of a competition for calcium ion by the cetyl sulfate anion to precipitate calcium cetyl sulfate and by the compound tested to precipitate a calcium salt or form complex calcium ions.
On the basis of the equilibria involved an estimate is made of the approximate solubility of calcium cetyl sulfate in the salt solutions tested.
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