ß :i"•'i anionic or cationic, provided that ?: the molecular weights of the mater- "ials to be determined are known or ' can be assumed. A solution of a '• known weight of an anionic detergent ß :• is made and chloroform and a small ? quantity of indicator solution, acid :11..: methylene blue, is added. The !:•. mixture is shaken and the dyestuff is taken up into the chloroform layer which settles out as a blue bottom layer on standing. ß A standard solution of a cationic agent, usually cetyl trimethyl am- monium bromide solution, is then run in from a burette with constant shaking of the container and the blue colour gradually begins to distribute •' itself into the upper aqueous layer and when the anionic complex is exactly formed, i.e., at the end point of the titration, the blue dye is equally distributed between the 'i:: aqueous and chloroform phase. By • suitable calculation the percentage ß active matter is then calculated. 2. Total Fatty Matter Content. Sulphation reactions are essentially reversible reactions and it is possible by boiling with, for example, 50 per cent hydrochloric acid to convert sulphated products back to the original fatty material. For example, a sulphated fatty alcohol can be split back to its constituent fatty alcohol and this can be extracted by a suitable solvent, normally ethyl ether, washed with water, the ether layer dried and the solvent removed by distillation, thus leaving the fatty alcohol behind. This can be weighed off and gives a very con- yenlent method for calculating the DETERGENTS percentage of fatty material in sul- phate. d compounds. This is usually expressed as "percentage total fatty matter" or T.F.M. 3. Free Fatty Matter. Being re- versible reactions sulphations cannot be carried out to completion and there is always a certain amount of unsulphated fatty matter present in the commercial products. This can be extracted from a dilute alcoholic solution of a sulphated product by shaking with petroleum ether. The petroleum ether layer contains the free fatty matter and can be separ- ated off, washed, dried, distilled and the residue weighed off and calculated as "percentage of free fatty matter," or F.F.M. The difference between the per~ centage T.F.M. and percentage F.F.M. represents the combined or sulphated fatty matter, and from this figure the percentage of active ingredient can be calculated, provided the type of alcohol is known or can be determined. In all sulphation reactions the aim is to get as high a combined fatty matter or as low free fatty matter as possible, and ratios of 58:1 in a finished sulphated alcohol powder can be obtained by careful control of manu- facturing conditions. 4. Water Content. It is normal to determine water contents by any of the standard methods of analysis. A particularly useful method is the Dean and Stark method--the product being tested is added to a water immiscible high boiling- point solvent such as toluene or heptane. 211

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS On heating, the solvent is dis- tilled over and carries with it the water, which can be separated and the amount of water easily read off if the distillate is collected in a suitable graduated tube. 5. pH. It is normal to determine the acidity or alkalinity of a product by use of a pH meter, using a solu- tion, say, of 2 per cent. strength. 6. Fillers and Builders. These are checked and determined by the normal methods of inorganic chemistry. 7. Evaluation. There are count- iess methods of evaluating surface- active agents. The three main types of evaluation for cosmetic purposes are: (a) determination of the surface tension and wetting power (b) the determination of lathering power, and (c) practical shampob testing. Surface tension is normally deter- mined by either the drop weight method or by the use of a tensio- meter, but surface tension figures do not appear to have much practical significance with regard to deter- gency. The Drayes & Herbig wetting out test is also sometimes used. Lathering power is determined in many ways, the three standard methods being (a) shaking a solution of the deter- gent a standard number of times and reading off the height of foam (b) the use of a metal plunger after the style of the old-fashioned Horlicks mixer to raise a foam, and (c) the method developed by Ross & Miles. In this method 200 cc/s of a dilute solution of surface-active agent is allowed to fall at a predetermined speed and from a standard height into 50 cc/s of the same solu- tion contained in a water- jacketed tube. The height of foam after the solution has been dropped is noted and readings are taken at intervals over half an hour. Various modifications of these methods are used, some laboratories preferring to add an artificial soil to a solution before foam- ing, and each laboratory uses its own particular variation of the method. The best practical method of evaluating surface-active agents in- tended for use in the cosmetic field appears to be an actual shampooing test, and this is normally carried out by the larger manufacturers in hair- dressing saloons under 'very strictly controlled conditions, often using the half-head test technique whereby the hair is washed first on one side and then on the other side with standard solutions of different pro- ducts. The hairdresser performing these half-head tests is specially trained to watch out for and note such things as harshness, the amount of foam from a given quantity of shampoo, appearance of dandruff after repeated washings, etc., and a very comprehensive system of testing can be easily worked out. 212