THE ANALYSIS OF SYNTHETIC DETERGENTS 525 alkaline solutions, which underlines the need for a better indicator that is usable at low pH values. The other field of much current endearour is the development of analytical methods to deal with newer types of surfactants. The search for a detergent that is readily decomposed in sewage treatment plants is to a large extent concerned with derivatives of natural fats, particularly of tallow which is available in larger quantities than coconut and palm kernel oils derivatives are being made and tested at a faster rate than the necessary methods of analysis can be devised. The field of ampholytic surfactants is another in which new compounds are frequently appearing. When commercial con- siderations have led to a more stable pattern of supply and demand of both types of surfactant, then the analyst can develop procedures that are worthy of publication. This situation is not likely to be reached within the next year or two. (Received: 27th May 1963) REFERENCES Many references given in the first paper below have not been listed again. The books referred to under 4 and 7 below are useful general works, and the former contains a good guide to the literature, excluding the anionic-cationic titration. • Smith. W. B. Analyst 84 77 (1959) 2 Holness, H., and Stone, W.R. Analyst 82 166 (1957) a Rosen, M.J. Anal. Chem. 27 787 (1955) 4 Rosen, M. J., and Goldsmith, H.A. Systematic Analysis of Surface-Active Agents (1960) (Interscience, London) 5 Drewry, J. Analyst 88 225 (1963) 6 Gaspari6, J., Borecky, J., Obruba, K., and Hanzlik, J. Collection Czechoslovak Chem. Commun. 20 2950 (1961) * Longman, G. F., and Hilton, J. Methods for the Analysis of Non-soapy Detergent (NSD) Products (1961) (The Society for Analytical Chemistry, London) 8 House, R., and Darragh, J.L. Anal. Chem. 20 1492 (1954) 9 Voogt, P. Rec. tray. chim. 78 899 (1959) •0 Voogt, P. Proceedings, $rd World Congress on Surface Active Agents III 78 (1960) (University Press, Mainz) • Jones, J. H. J. Assoc. O.l•c. Agr. Chemists 28 398 (1945) •a Abbott, D.C. Analyst 87 286 (1962) •a Silverstein, R.M. Anal. Chem. 35 154 (1963) •4 Cullum, D.C. Proceeding, $rd World Congress on Surface Active Agents III 42 (1960) (University Press, Mainz) •5 Dolezil, M., and Bulandr, J. Chemicke Listy 51 255 (1957) •6 Schwerdtner, H., Teztil u. Faserstofftechnik 5 569 (1955) •? Marron, T. V., and Schifferli, J. Ind. Eng. Chem. Anal. Ed. 18 49 (1946) •8 Blank, E. W. Soap Chem. Specialties $4 41 (January 1958) •9 Chinnick, C. C. T., and Lincoln, P. A. Proceedings, 1st World Conference on Surface Active Agents I 209 (1954) (Chambre Syndical Tramagas, Paris)

52•3 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS I)ISCUSSION )/IR. G. A. C. PITT: What indicators have you tried other than methylene blue and bromophenol blue ? THE LECTURE•: Among anionic indicators, methyl orange is the only alternative to bromophenol blue that we have used. A wide range of indicator types is available, but bromophenol blue has so few disadvantages that there is little incentive to look elsewhere. With cationic indicators the situation is quite different, and we have considered every coloured organic cationic compound that has been brought to our attention. Dimidium bromide was mentioned above, and methyl yellow has also been used by us. Indicators such as methyl violet and methyl green gave less satisfactory results than methylene blue pinacyanol chloride and methylviologen showed no promise. We think that the problem justifies attempts at the special synthesis of an indicator, and some coloured organic compound contairfing one quaternary ammonium group and no other ionogenic group in the molecule would probably be suitable. MR. J. S. LEAH¾: Has the use of thin layer chromatography been in- vestigated in place of paper chromatography in the qualitative analysis of detergents ? It would appear to have advantages both in time and possibly conditions of detection. THE L•C•URER: We have not investigated the subject and do not know of any work on thin layer chromatography of detergents. In view of the apparent advantages we hope to look into the technique when time is available. A M•M•ER OF •H• AUDIENCE: How is phosphomolybdic acid used ? THE L•c•u•n•: Phosphomolybdic acid is slowly added to a dilute acid solution of the non-ionic surface active agent and of barium chloride, and the non-ionic compound M is thereby precipitated as the complex B%(PM%204o)2.xM. The precipitate is filtered off, dried, and weighed. The composition of the precipitate is then determined by dissolving a weighed portion in excess of alkali and back-titrating the excess. The overall reaction is :-- B%(PMo•20•0)• +46 NaOH +3 Na•SO4 =3BaSO•-.4-24 Na•MoO• + 2 Na•HPO•+22 H20 For a precise end-point we back-titrate to excess with hydrochloric acid, then add a little neutral sodium sulphate, and titrate again with sodium hydroxide. This reduces the interference due to carbon dioxide, which may be appreciable when soluble barium salts are present. Since 460 ml 0.1N sodium hydroxide are equivalent to 4057 mg of barium phosphomolybdate,