JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS DETERMINATION OF THE ACTIVE DETERGENT The fact that certain cationic surface-active agents react stoichiometric- ally with anionic surface-active agents has been used as a basis for estimating the latter. In the method of Hartley and Runnicles • the anionic material is titrated with the cationic surface-active agent using bromo-phenol blue as an indicator to detect the excess. The colour change from purple to blue is judged rather than observed and is not easy to detect, even after considerable experience. In the method of Barr, Oliver and Stubbings 7, the artionic material is titrated with the cationic surface-active agent using a chloroform and an aqueous phase with bromo-phenol blue indicator, taking the first' indication of blue colour in the chloroform phase as the equivalence point. The actual end point is somewhat indefinite and requires comparison with similar mixtures containing first, insufficient, and second, excess of the cationic surface-active agent. In the method of Epton 8 the artionic material is titrated with the cationic surface-active agent using a chloroform and an aqueous phase with methylene blue indicator and taking the equivalence point when the two layers are visually the same. This method is superior to the other two methods and gives readily reproducible results. A weight of sample is taken to give an approximately 0.002 molar solution when dissolved in one litre of distilled water, and 25 mls. are pipetted into a 100 mi. glass-stoppered measuring cylinder. To this are added 15 mls. of chloroform and 25 mls. of methylene blue indicator solution the cylinder is stoppered, shaken vigorously and allowed to stand for one minute, when it will be seen that the deep blue colour of the indicator is concentrated in the chloroform layer. An 0.002 molar solution of cetyl trimethylammonium bromide is added 1 ml. at a time, shaking vigorously after each addition. The depth of the blue colour in the chloroform layer will diminish while the blue colour of the aqueous layer will increase. When the colours are nearing the same depth the additions are made in lesser amounts until finally an addition of 0.1 mi. will cause the colours to be visually the same when viewed in reflected light. The first titration is taken as a guide and two further titrations are carried out and should agree within 0.1 ml. The result is cal- culated to terms of equivalent weight and, using the average molecular weight of the alkyl sulphate obtained from the previous determination, is expressed as a percentage of alkyl sulphate. Cetyl trimethylammonium bromide is preferred to cetyl pyridinium bromide because of its greater solubility in water, and the material is standardised by precipitation with standard potassium dichromate solution, the excess dichromate being measured iodometrically. g The methylene blue indicator solution is prepared by dissolving 50 gins. of anhydrous sodium sulphate in distilled water, adding 120 mls. of 2N sulphuric acid, 6 mls. of 0.5 per cent aqueous methylene blue solution and diluting to one litre. 126

THE EVALUATION OF COMMERCIAL ALKYL SULPHATES DETERMINATION OF THE FREE FATTY ALCOHOLS The unsulphated fatty alcohols may be determined by extraction of a solution of the material with a suitable solvent or by extraction of the material after the addition of sufficient anhydrous sodium sulphate to combine with the water present. The latter method is preferred. A weight of 2 gms. of sample is transferred to a small beaker and 10 gms. of anhydrous sodium sulphate added. The mixture is thoroughly stirred with a small glass rod and 50 mls. of hot benzene added. The contents of the' beaker are thoroughly mixed and allowed to settle for a few minutes on a water bath. The benzene extract is filtered through a No. 1 Whatman filter paper into a weighed flask and the extraction repeated twice more, transfer- ring the contents of the beaker into the filter with the last extraction. Most of the benzene is removed by distillation, the last traces removed in a steam oven and the flask cooled and weighed. The result is expressed as a percentage of free fatty alcohols. DETERMINATION OF THE INORGANIC SULPHATES The inorganic sulphates are determined by solution of the alkyl sulphate in 95 per cent alcohol and removal of the inorganic salts by filtration. The sulphates are precipitated as barium sulphate. A weight of 2 gms. of sample is heated with 50 mls. of 95 per cent alcohol until the alkyl sulphate has dissolved and the inorganic salts are allowed to settle on a water bath. The solution is filtered through a Gooch crucible containing a close-fitting No. I Whatman filter paper and the inorganic salts are transferred to the crucible and thoroughly washed with hot 95 per cent alcohol. The contents of the crucible are then transferred back to the original beaker with hot distilled water, the bulk adjusted to I00 mls., and 4 mls. of concentrated hydrochloric acid added, followed by 20 mls. of hot 10 per cent barium chloride solution. The contents of the beaker are boiled for one minute and allowed to stand at least four hours. The precipitate of barium sulphate is filtered through a No. 42 '•Vhatman filter paper and washed and ignited in the usual way. The weight of barium sulphate obtained is expressed as a percentage of sodium sulphate. DETERMINATION OF THE INORGANIC CHLORIDES The inorganic chlorides are determined by Mohr's method of direct titration with standard silver nitrate solution using potassium chromate indicator. A weight of 2 gms. o[ sample is dissolved in approximately 200 mls. of distilled water, and if the solution is alkaline to litmus, dilute nitric acid added to neutrality. Potassium chromate indicator solution is added and 127