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

SYNTHETIC DETERGENTS COMMERCIALLY USED SURFACE-ACTIVE AGENTS For cosmetic purposes the sul- phated fatty alcohols and sulphated olefines probably are the most used products. The secondary alkyl sul- phates exemplified by Teepol are available as sodium neutralised pro- ducts in liquid form with a tendency to shed crystals in very cold weather. The lauryl sulphates are usually' presented as triethanolamine or other amine salts, and as sodium salts. Various grades of lauryl alcohol are used, depending on the end use of the product. As will be appreciated, "Lauryl" includes a whole range of alcohols from coconut and palm kernel hydrogenates down to the highly fractionated, almost pure C, alcohols. The sulphated mono- glycerides and sulphated alkylola- mides are usually used as powders. The sulpho acetates have been proposed in America for use as shampoos, but have so far not found application in this country. In certain countries, particularly in the Middle East, the alkyl aryl sul- phonateshave been used in shampoos, although so far they have usually been considered to be too harsh for use in cosmetics. Some of the non- ionics have been used, but their comparative lack of foam is a factor against their use. The sulphonated oils are still used to a small degree and the cationics have not yet appeared in force in shampoos, although some cationks are used in anti-dandruff shampoos. Recently cationics have been under a cloud, due to certain difficulties with respect to the causing of corneal opacity with a cationic-nonionic product in the United States. Within recent months considerable interest has been shown, particularly in the United States, in the possible causing of eye irritation due to deter- gents. A test is made in which a solution of the detergent under test is instilled into the conjunctival sac of one of the eyes of a rabbit, the other being used as a control. After a few seconds the eye used for the test is examined and thereafter regular observations for inflamma- tion and injury are made. By this test the following gradation of pos- sible irritation is seen: cationks greater than anionics--anionics greater than nonionics. A grading has been suggested of 10:1:0.5 -- 1.0. Perhaps now it will be advantage- ous to say a few words about the formation of Micelies. It is known that within a certain limit of con- centration for amphipathic electro- lytes a considerable difference in physical properties becomes appar- ent. This is caused by the aggrega- tion of the ions in aqueous solution to form ionic Micelies. The critical concentration for Micelie formation has been deter- mined by Corrin & Harkins for various materials by the use of an indicator method. They describe (Journ. Amer. Chern. Soc., March 1947, pages 679-683) the method of the determining of critical concentra- tion by titrating detergent solutions containing dye against the dye stuff solution. The dyes used were Pina- 213