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,

THE ANALYSIS OF SYNTHETIC DETERGENTS •59.7 the inorganic content of the precipitate can be calculated. The rest of the precipitate comprises the non-ionic surface active agent the content of which in the original solution is thus determined. An analysis of the precipitate is essential for every new type of non-ionic compound, because the value of x varies from one substance to another, and may even vary among com- pounds of nominally the same composition. Ml•. D. B^ss: Your method of analysis for ampho!ytics is to estimate as cationics under acid conditions. This method works well for the sub- stituted amino acid type, but do you obtain good results using the betaine type of ampholytic ? I am thinking in particular of difficulties when there is a degree of internal compensation within the molecule as with the cyclo- imidinium type. T}m LECTURER: Yes, we find our normal method for cationics to be satisfactory for the betaine type of surface active agent. The two-phase titration is performed in acid solution with chloroform as the organic phase, sodium dodecylbenzenesulphonate as titrant, methylene blue as indicator, and we take complete transference of colour to the organic phase as the end-point. BOOK REVIEW Standard Methods of Chemical Analysis. Volume II (A and B). INDUSTRIAL & NATURAL PRODUCTS & NONINSTRUMENTAL METHODS. Sixth Edition. Editor: F. J. Welcher. Part IIA--Pp. xiv q- (1-1282) q- Ill. Part IIB--Pp. xi q- (1283-2613) q- Ill. (1963). D. Van Nostrand Company, Inc., New York. $25 each (not sold separately). It is almost twenty-five years since a revised edition of Standard Methods of Chemical Analysis has appeared. In 1939, the Fifth Edition was published as two volumes but so great have been the modifications, refinements and developments of the methods of chemical analysis since that time that the Sixth Edition appears in three volumes, with Volume II expanded into two parts, bound separately as Volume IIA and Volume IIB. Despite its considerable expansion the purpose of Volume II remains that it shall be a collection of carefully selected well proved methods of technical analysis, of practical value to the professional chemist. The lay-out of this edition is similar to the previous one, but the expansion due to the inclusion of new material adequately reflects some of the important changes that have taken place in recent years in analytical techniques. The expansion includes chapters on standard laboratory apparatus detection of cations and anions mechanical separation separations by filtration separations by electrolysis solvent extraction separations by distillation and evaporation chromatography ion exchange methods in analysis acid-base titrations in non-aqueous solvents statistical interpretations quantitative organic analysis air pollutants amino acid analysis of protein hydroly- zates chemical analysis in clinical medicine fertilizers gas analysis with emphasis on vacuum techniques pesticides plastics silicates, glasses, rocks, soils and vitamins. There are numerous references to original papers and there is a good index at the end of Part B only. It is somewhat annoying that Part B has to be consulted for work that is known to be found in Part A, for these books are not lightweight ones. It is difficult to understand why the index was not included in Part A as well the book would only be 22 pages larger than Part B had this been done. Cosmetic chemists may be disappointed that the analysis of cosmetics does not