JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the solution titrated with 0:1N silver nitrate solution. ß The result is expressed as per cent of sodium chloride. DETERMINATION OF THE WATER CONTENT Oven-drying methods are not satisfactory for the determination of the water content since the alkyl sulphates decompose with prolonged heating, particularly at temperatures above I00 ø C. Apart from this the material usually contains some unsulphated alcohols which may be volatile during the heating process. If such a method be used it could only be suitable for comparative values obtained under standard conditions, such as drying for one hour at 95 ø C. The method of direct titration of the water with Fischer's reagent is suitable if there is a need for this reagent to be regularly used, since it is not convenient to prepare for only occasional water determinations. A more generally suitable method is using the Dean and Stark apparatus, and Burton and Robertshaw •ø use .this method for determining the water content of sulphated fatty alcohols. Since they experienced some decom- position of the sulphated alcohols when using xylene, they preferred the lower boiling-point heptane, but xylene is generally satisfactory for alkyl sulphates and is more rapid. A convenient weight of sample is transferred to the flask and 70 mls. of xylene, 60 gms. of oleic acid and a small amount of broken dried porous plate or pumice are added. The apparatus is assembled and the graduated receiver filled with xylene. Distillation is commenced and continued until the solvent distils over clear and drops of water cease to fall from the reflux condenser. The receiver is cooled to 20 ø C. and the volume of water noted and expressed as a percentage. The oleic acid is used to prevent undue frothing and is dried by heating to 140 ø C. and cooling in a desiccator. The methods given here may be applied in general to commercial alkyl sulphates which are usually supplied as the sodium, triethanolamine or ammonium salts and may be in the form of liquids, pastes or solids. They may be applied also to similar salts of sulphated ethylene oxide condensates of fatty alcohols, and in the case of this type of detergent, if the molecular weight of the fatty alcohol before condensation with ethylene oxide is known, the hydroxyl value can be used also to ascertain the number of molecules of ethylene oxide present. The evaluation of a commercial triethanolamine lauryl sulphate as carried out by two independent analysts is shown in Table I and a similar evaluation of a commercial sodium lauryl sulphate is shown in Table II. In the case of the latter, the sample was found to contain small amounts of carbonate and bicarbonate, which were determined in the inorganic salts before precipitation of the inorganic sulphate. 128

THE EVALUATION OF COMMERCIAL ALKYL $ULPHATES TABLI• I COMMERCIAL TRIETHANOLAMINE LAURYL SULPHATE Analyst Analyst A B ... Total Fatty Alcohols % 21.4 21.7 21.5 21-3 Hydroxyl Value of Fatty Alcohols 281 283 281 285 Average Molecular Weight of Fatty Alcohols 200 198 200 197 Average Molecular Weight of Alkyl Sulphate .•428 426 428 425 Triethanolamine Lauryl Sulphate % 44.4 44.3 44.5 44-2 Free Fatty Alcohols % 2-7 2-5 2-4 2.3 Inqrganic Sulphate as Na•SO4 % 0-1 0.1 0-! !0.1 Chlorides as NaC1% 0.9 0.9 0.9 0.9 Water % 50'0 50.4 50.6 50.9 TABLE II COMMERCIAL SODIUM LAURYL SULPHATE Analyst Analyst A B -- Total Fatty Alcohols % 53.4 53.5 53-2 53.6 54.1 Hydroxyl Value of Fatty Alcohols 285 286 287 288 290 Average Molecular Weight of Fatty Alcohols 197 196 195 195 194 Average Molecular Weight of Alkyl Sulphate 299 298 297 297 296 Sodium Alkyl Sulphate % 55.8 55.6 55-4 55.4 55.3 Free Fatty Alcohols % 17.1 17.0 16-8 16-4 16.5 Inorganic Sulphate as Na•SO• % 10-5 10-8 10.6 10-4 10.4 Chlorides as NaC1% 0.1 0-1 0.1 0.1 0.1 Bicarbonate as NaHCOa % 0.7 0.6 0.6 0'6 0-5 Carbonate as Na•COa % 1-8 2.0 1.8 1.8 1.8 Water % 15.5 15-5 16.0 16.0 16.2 ACKNOWLEDGEMENT The author wishes to express his thanks to the Directors of County Laboratories, Limited, for permission to publish this paper. REFERENCES • J. A. Gilby, H. W. Hodgson, Manf. Chem., 1950, XXlo 371-376, 423-426. 2 I•. Linsenmeyer, Melliand Textilber, 1940, 21, 468-469. a Analytical Methods Committee of the Society of Public Analysts and Other Analytical Chemists, Analyst, 1951, 76, 279-286. 4 C. L. Ogg, W. L. Porter, C. O. Willits, Ind. Eng. Chem. Anal. Ed., 1945, 17, 394-397. 5 S. Siggia, Quantitative Organic Analysis via Functional Gyoups, 1949, p. 3. John Wiley & Sons, New York. 8 G. S. Hartley, D. F. Runnicles, Proc. Roy. Soc., 1938, 168A, 424. 7 T. Barr, J. Oliver, W. V. Stubbings, J. Soc. Chem. Ind., 1948, 67, 45. s S. R. Epton, Nature, 1947, 160, 795. 9 2•ritish Pharmaceutical Codex, 1949, 232. x0 D. Burton, G. F. Robertshaw, Sulphated Oils • Allied Products, 1939. A. Harvey, London. 129