266 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the prescribed limits, the gas flow must be carefully regulated and sudden surges avoided. Moreover, there is always some loss of bromine from the potassium iodide trap and this amount will vary with the conditions of the experiment, and particularly with the temperature of the immediate sur- roundings. It is therefore necessary to run a blank experiment occasionally to determine this loss. A recent paper TM describes in detail the application of this method to a number of polyoxyalkylene compounds. Table 1 DETERMINATION OF ETHYLENE OXIDE Per cent Ethylene Oxide _ Morgan's Siggia's Method Method Theory Ethylene glycol 70.4 71.0 71.0 68.8 71.0 69.3 72.5 Lissapol N 16.5 17.1 16.9 17.0 17.7 Ucon LB. 625 76.5 [ 79.9 74.7 78.8 Lauryl polyoxyethylene alcohol 39.2 40.6 39.9 39.7 39.5 The second method of determination, due to Siggia' 9, although based on the same reaction, is by way of contrast almost fantastically simple. Siggia makes the assumption, which is quite valid if Morgan's equation is accepted, that the amount of free iodine produced in the reaction is proportional to the alkylene oxide content of the sample. The apparatus consists of the reaction flask and condenser previously used, together with a simple trap to prevent escape of iodine vapour. At the end of the reflux period, the iodine in the reaction flask is titrated with standard sodium thiosulphate and the alkylene oxide content calculated from the titre. A blank experi- ment has to be carried out with the same amount of hydriodic acid as the latter always contains some free iodine. In order to reduce this blank to as low a figure as possible the hydriodic acid should be freshly distilled. The original method suggested a simple grease trap to collect iodine vapour, but in our own laboratory a potassium iodide trap has been found more satisfactory. 1 ml N/10 Na2S•O• =_ 0.002203 g C•H40 For investigational and comparative purposes both methods may be carried out simultaneously on one portion of the sample. Our own results indicate that Siggia's method gives results which are

CHEMICAL ANALYSIS IN THE COSMETIC INDUSTRY 267 •nore reproducible than those obtained by Morgan's method. Propylene oxide derivatives tend to give low results by both methods. A more mundane subject which frequently requires the analyst's atten- tion is the determination of water. In some cases, the amount of water present is in itself important and in the case of unknown samples it tells the analyst how much other material he has to seek. The time-honoured •nethod of oven drying is non-specific and only applicable in the absence of other volatile ingredients. In cosmetic products, perfume, alcohol and glycerol will volatilize wholly or in part and the method is only of limited application. Even mineral oil can lose up to 5 per cent on drying at 105 ø C. Table 2 DETERMINATION OF WATER Percentage water w/w Preparation Distillation Distillation Distillation Distillation Karl Loss at Toluene n-heptane Xylene Benzene Fischer 105 ø C. W/O Emul- sion Theory 58-65% 55.8 55.75 58.2 59.6 70.7 61-9 -- O/W Emul- sion 78.5 77.4 78.7 -- 81.4 80-4 Toothpaste Theory 20.7% 20.5 20.6 21.8 19.9 30-3 23.2 Toothpaste Theory 21.4% 30.3 25.3 32-8 21-1 -- -- The method of Karl Fischer is probably the most specific of the methods in general use, but it is limited to those substances which do not react with the Fischer solution, which consists of iodine and sulphur dioxide in methanol and pyridine. Unfortunately, many cosmetic products contain perfume ingredients which interfere with the Fischer method. The method which seems to be most generally applicable to cosmetics is distillation with an immiscible solvent, originally due to Dean and Starke This method, which has been modified by a number of workers2•,22, TM, is not one of high precision, but it gives results which are accurate enough for most purposes and it is applicable to a fairly wide range of cosmetic products. Like the other methods, this too has its limitations, and the two substances which are most likely to cause interference are glycerol and alcohol. The interference due to glycerol can be overcome by selecting the right entrainer and limiting the time of distillation. Some experiments on the determination of water by the three methods outlined above were made in the author's laboratory. (Table oe.) The first