JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS' 4. Breakdown or separation of the emulsified oils. This can be a very serious problem in cold wave solu- tions that have a white or milky appearance. The clouding agent must be selected with great care and the finished product subjected to thorough testing in the laboratory. 5. Perfume difficulties. Perfumes have. noi: been too successful in covering the ammoniacal and thio- glycollate odour of cold 'wave solu- tions, but they are used in many preparations. Although the odour character of the perfume may change with age, a far more serious problem occurs when the perfume oil is thrown out as small globules. 6. Fading or change in colour when dyes or other coloring matters are used. ß Since cold wave solutions are powerful reducing agents, many dyes which may be used to colour the solution .are unstable. Very few of the certified colours show satisfactory stability in cold wave solutions, but accelerated laboratory stability tests ,will usually weed out the dyes that are unsatisfactory. ß 7. Formation of sediment or crys- tals in .the solution. These are usually insoluble organic sulphur compounds and may be found when an inferior grade of thioglycollic acid is used. Any method of accelerated stabil- ity testing of cold wave solutions must be-able to evaluate both chemical and physical changes in the product. Two significant chemical changes which may occur are a fall in the pH value and in the thioglycol- late concentration. And changes. 184" which may alter the appearance of the product are emulsion breakdown, perfume separation, or discoloration. Bottled samples from each batch of cold wave solution should be shelf- tested for at least a year and exam- ined frequently to check for emul- sion breakdown or discoloration. They should be assayed for thio- glycollate by iodimetric-titration- and the' pH accurately .determined.- Samples can also be tested for heat stability at 100 ø and 120 ø, and cold tested at 35 ø to 40 ø F. Both heat and cold tests can run up to 30 days and longer, after which the solution is again assayed for thioglycollate and the pH determined.. Accelerated shelf tests, such as sustained heat at 100 ø to 120 ø, will .usually reveal whether or not the emulsion, per- fume, wetting agent and colour are stable and compatible in the presence of alkaline thioglycollate. During the early years of cold. wave development an accelerated test that was occasionally used was to bubble a/r through a cold wave solution and assay the solution at frequent intervals.' When ammonia • was used as the alkali the pH con- tinued to drop, due to loss of ammonia, and the rate of oxidation.: decreased. When fixed alkalis were used, the rate of oxidation often. indicated the presence or absence trace metal. catalysts or the effect,? • if any, of the various additives such: :. is perfume, clouding agent, we.tting?i agent, etc., on the rate of oxidatiom:ii: I An accelerated test that I have used was similar to this but precise. In an apparatus similar

F• Ili• :':i:i' STABILITY TESTING OF ! ,,arance to a Van Slyke am•no :: •gen set-up, a measured volume finished cold wave solution was ,,chanically shaken with a measured of oxygen and at intervals a was drawn off and the rate oxidation determined. Whole :Series were run on various formula- to eliminate those materials tended to catalyse the oxida- of thiog]ycollate to dithiogly- Cold wave preparations are given ii•milky white appearance by the of an oil or resin generally as a concentrated emulsion resin dispersion. Of course, such an emulsion must be stable and com- with alkaline thioglycollate. iii:i•!!Any accelerated test generally used ??iii'for dilute emulsions can be used ?/here too. Heat and cold tests, alter- i?ji?:hating heat and cold tests, and }?•(:i'mechanical agitation, all have value. •f- •ii!i:ilAn accelerated test. that is' often i?i:i:•:Used, especially for dilute emulsions •i•-i: i::.i::in the presence of electrolyte, is to ?i::?centrifuge the product at speeds •:•? 'from 1,500 r.p.m. upward. The more. '•:•i:•:Unstable the emulsion, the greater 'iii!1111 ::the creaming or separation when •??::centrifuged. 5(ii'::i:.i It has been my experience that :ilklief:Cold Wave preparations properly 517: formulated from kigh-quality raw ':(i ?:' i material showed no appreciable .'?:i'? change in both chemical properties :?i:and appearance even after several :ill?? years. i)?::: DEALING WITH SHAMPOO }: i: PROBLEMS HAIR PREPARATIONS trouble-free shampoos might appear to the uninitiated to be a simple matter--and perhaps it was, when the shampoos were all clear, liquid soap preparations. Now we have, in addition to soap shampoos, synthetic detergent shampoos and the so-called oil shampoos. These, in turn, may appear as milky sham- poos and pearly shampoos, egg shampoos and beer shampoos, conz centrated shampoos and powder shampoos, cream shampoos and clear shampoos, deodorant shampoos and colour shampoos, chlorophyll sham- poos and curl shampoos and, more recently, pressur/sed foam shampoos. And each one poses its own special problems .... If you were to •sk "What can go wrong with a shampoo?" my answer would be, "Almost everything." Clear shampoos cloud up, viscous shampoos thin out, milky shampoos separate, pearly shampoos settle, egg shampoos coagulate, and cream shampoos either Set too hard or become soupy. These are just some of the problems that arise: there are many more. Two very important determina- tions that are frequently made 'on most shampoos are the pH and viscosity. A change in pH usually means trouble ahead and so.. this value should be checked often and especially after all accelerated stabil- ity. tests. A reliable and rapid routine method for determining the viscosity of liquid shampoos is by use of a plastic viscosity cup with a fixed and accurate aperture. The time, in seconds, to fill a 60 ml. 185