Summary 1. The measurement of the foaming properties of soaps and detergents is shown to be possible by comparing the relative stability of a foam by measuring the effect of an arbitrary standard destructive mechanism acting upon a volume of foam during production under standard conditions and protected from adventitious destructive forces. 2. A simple apparatus and procedure for carrying out foam tests has been described and the reproductibility of the test evaluated. 3. Previous studies of foam comparison have been reviewed and criticisms offered regarding the procedures and conceptions involved.

The observation of minima in the surface tension-concentration curves for aqueous solutions of various surface-active materials has been the cause of considerable conjecture. Pownev and Addison (12), in particular, found welldefined minima in the surface tension of solutions of sodium salts of primary alcohol sulfates containing from twelve to eighteen carbon atoms. The minima are as much as 5 dynes per centimeter lower than the value reached at higher concentrations. These "anomalous" results have presented apparent disagreement with Gibbs' adsorption equation. The hypotheses proposed to reconcile such incongruities have been frequently discussed (1 to 12).Usually the explanations proposed fall into two groups: First, it has been claimed that there are experimental difficulties which result in errors in the methods used for measuring surface tension (3, 4, 7). On the other hand, the possible existence of abrupt changes in colligative properties of solutions of certain surface-active substances has been emphasized ( 12) and this could lead to minima in the surface tension-concentration curves.The data which we present here deal with solutions and procedures not covered by either of the above explanations. PROCEDUREThe sulfated alcohols used in this work were of a particularly high degree of purity. The details of the methods used in their preparation are given in a report entitled "Some Properties Involving Surface Activity of Sodium Salts of Primar}* and Secondary Alcohol Sulfates" (5).

The preparation and properties are described for alternate members of a homologous and of an isomeric series of purified sodium salts of secondary alcohol sulfates, containing from 11 to 19 carbon atoms, and for a straight hydrocarbon chain with the sulfate group in various positions. The purified sodium salts of the primary alcohol sulfates with 10, 12, 14, and 16 carbon atoms are also examined.Measurements have been made of the surface tension and foaming, wetting, and detersive properties of solutions of these compounds in water and with added electrolytes. Solubilities of sodium salts of the secondary and primary alcohol sulfates studied are reported at 50 intervals from 20°to 4(j°C. The data are discussed from the point of view of correlating changes in the properties involving surface activity when the structure and molecular weight of the compound are changed.

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