292 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS c) -r' .•,.lOO z= 5o 0'4 1 5 10 inorganic/Organic property Balance 1'5 Figure 4. Relationship between solubility of amino acids or their salts and their inorganic/organic property balance

1762 WATER-IN-OIL EMULSIONS 1:1,5 6 1279 0 1 2X104 i • 1:•3 12 1743 293 1:7., 21 1 2 30 50 82 cps 3170 0 1 2x10 • 1 2 1 2 102 3088 Figure 5. Rheological properties of gels obtained by combination of Sunsoft O-30B and 10 per cent aqueous solution of glycine: (*) Mixing ratio, (**) hardness (by curd tension meter), and (***) upper viscosity (by Ferranti-Shirley viscometer) DISCUSSION OF RESULTS The gels cannot be formed using any combination of surfactants and amino acids. To make the gelation possible, certain requirements in both surfactants and amino acids must not be neglected. Among the many surfactants tested, those capable of forming gels with aqueous solution of amino acids or their salts have been shown in Table I. It became evident from the results of the experiments, that the requirement common to the surfactants capable of forming gels were as follows. 1. Fatty acid partial esters of polyhydric alcohol having at least 3 hydroxyl groups in 1 molecule 2. inorganic-organic property balance (IOB) of the molecules were within the range of about 0.4 to 0.7 3. the carbon number of the esterified fatty acids was within 16 to 18 and 4. must be liquid at room temperature. As is evident from Table II, no gels were formed with the surfactants which do not meet the above requirements, such as glycol esters, low fatty acid glycerides, surfactants that are solid at room temperature, higher alcohol ethers, higher fatty acid esters, and ethylene oxide adducts. Polyhydric alcohols, which can be the main core of the gel forming surfactants were known from other experiments to include glycerin, diglycerin, trimethyl ethane, tri- methylol propane, pentaerythritol, sorbitan, and sorbitol. On the other hand, the fatty acid part of the surfactants includes, for example, oleic acid, isostearic acid, ricinolic