260 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS graphic alumina in the usual way, using a slurry of alumina and petroleum ether (b.pt. 40ø-60 ø C) to form the column and applying gentle suction. The sample (about 0.5-1.0 g) is dissolved in about 30-40 ml petroleum ether (b.pt. 400-60 ø C) and added through the top of the column, wash- ing-in with small portions of petroleum ether. Elute with the same solvent using about 200 ml in all, suck the column dry, transfer the eluate to a tared flask, evaporate the solvent on the steam bath, dry the residue at 60 ø C, cool and weigh. Often it is not practicable to use so much fat for one determination and a semi-micro modification, which has been in use in the author's laboratory for some time, yields results of precision comparable with those obtained by the standard method. In this modification the length of column is 100 mm and the diameter 12 mm, and as little as 0.1-0-2 g fat and a total volume of 60-70 ml solvent may be used. The residue will contain any hydrocarbons natural to the oils and fats used, but these will usually be very small by comparison with added mineral oil or petroleum waxes. A determination of iodine value on the separated hydrocarbons will reveal the presence of squalene. Recently two papers have been published •,• describing the chromato- graphic separation of the components of technical monoglycerides, using silica gel columns. Ion-exchange chromatography is a useful aid to the analyst, particularly in separating nonionic surface-active materials from ionic types. Newburger 7 has described a method for the analysis of shampoos, using Amberlite C45 resin, in which the alkyl sulphates, fatty acids and fatty alkanolamides are separated. The method described involves a lengthy procedure for the purification of the resin in order to prevent high blanks. A method for examining emulsions by passing them through ion-exchange columns has also appeared 8. It would be inappropriate to leave the subject of chromatography without some reference to the newer technique of gas chromatography. By the use of this elegant technique it is possible, using a very small sample, to separate and determine the components of a mixture of homologues, and in many cases results are obtained which are unattainable by any other method. Classical analysis deals very largely in averages. In the examination of essential oils, for instance, alcohols, aldehydes and esters may be separately determined by the usual methods, but the results are usually calculated by using the molecular weight of the predominating member of the group. It is often useful to know' the proportions of the individual compounds present and gas chromatography is so sensitive that it often detects unsus- pected components. If the so-called lauryl alcohol is subiected to gas- liquid chromatography, using a suitable stationary phase, a whole series of

CHEMICAL ANALYSIS IN THE COSMETIC INDUSTRY 261 alcohols will be found to be present, n-dodecanol being the predominating compound. The individual alcohols and their concentration in the sample can be determined in this way. The literature on gas chromatography is already considerable and two papers have appeared in this Journal recently9,•0. The first deals with the analysis of aerosol products and the second with essential oils and synthetics •ø. Semi-micro techniques have gained considerable attention in recent years and they have many advantages over the corresponding macromethods. There is much saving in time and material, and processes which tend t•o become tedious on the macroscale are accomplished with ease when reduced to semi-micro proportions. The advantage of the semi-micro over the micro- technique lies in the fact that special apparatus is not usually needed, methods and apparatus require only slight modification and manipulation is easier. Strictly, semi-micro analysis deals with samples from 10-50 mg, but the term is frequently used with reference to rather larger amounts than this. However, it rather depends on the nature of the sample and what is being determined. One might easily start with an amount of sample within the macrorange and yet, when all the processes are finished, the final determination may still rank as semi-micro. Such a case might occur when determining nitrogen, by the Kieldahl method, on a sample having a very low nitrogen content. In order to achieve a suitable final titration it might be necessary to use an amount of sample outside the generally accepted semi-micro range. The hydroxyl value, determined by a British Standard Specification TM, in which the fat is acetylated with a mixture of acetic anhydride and pyridine, and the residual acetic anhydride is hydrolysed with water and titrated with alcoholic potash, normally requires 1-2 g of the sample according to the expected hydroxyl value. A modified semi-micro procedure, which yields excellent results if practised with care, is as follows ß Weigh accurately about 0.2 g of the sample into a 100 ml flat-bottomed flask, with a ground glass joint and add, from a 1 ml straight-tube pipette, 1 ml of acetylating agent. (1 volume AR acetic anhydride ß 4 volumes AR pyridine.) To another similar flask add 1 ml of the reagent, from the same pipette, using exactly the same technique and time of draining. Fit a straight air condenser of about 20 cm length, and heat on the boiling water bath for 45-60 minutes. At the end of this period, add 5 ml of water through the top of the condenser, mix thoroughly and re-heat for 5 minutes. Allow to cool to room temperature and wash down the condenser with about 20 ml n-butanol, disconnect the condenser and wash the joint with a little more butanol. Add 1 ml 0.1 per cent phenolphthalein