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

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS receiver at 80 ø F. is the viscosity value that is used. The rotating spindle type of viscosimeter such as the Brook field instrument is not satisfactory for viscous liquids that tend to be thixottopic. As the spindle rotates, the liquid in contact with the rotating spindle thins out and a constant reading is unobtain- able. ß A very important test for all dear liquid shampoos, whether of the soap, detergent or oil types, is the cold test. Not only is the cloud point determined but also the temperature at which the liquid becomes clear. These two values are not always the same, especially where the shampoo contains sodium lauryl alcohol sulphate. This par- ticular detergent,' which is exten- sively used in shampoos, is not too soluble and tends to crystallise out of solution in the temperature range of 45-55 ø F., but, what is still worse, is that it might not redissolve until the solution is warmed to 70 or 75 ø F. These temperature values will vary with the concentration and composition of the shampoo' and must be-carefully checked. Milky or pearly liquid shampoos may settle or separate, and 'oven tests at 100 ø and 120 ø F., centrifuga- tion,-and exposing the shampoo to prolonged vibration, are all useful accelerated stabilit•r tests. One of the 'basic qualifications of.'a "good cream shampoo is that it should always have good texture and con- sistency, irrespective of the tempera- ture to which it has been exposed. Freezing, chilling to 350-45 ø F., 186 prolonged heating at 100 ø to 120 ø, are among the accelerated tests frequently used. ßAfter these tests the shampoo is permitted to reach room temperature and then carefully examined for any change. A very valuable tool in the examination of cream shampoos is the microscope. Shampoos of this type usually are a complex suspension and emulsion, •and changes in crystal structure and particle size after subjecting' the shampoo to accelerated stability tests is often an indication of impend- ing difficulty. Prolonged vibration is also a useful test. Egg shampoos, still enjoying con- siderable popularity in the United • States, contain either whole, frozen or dried eggs and should be tested for heat stability at 100 ø and 120 ø The protein is very-easily denatured .i7 by heat and may coagulate in the •.:( shampoo. White milky or cream shampoos ::iii have a tendency to become yellowish }• ß upon standing for several weeks months, especially if they containiiii unsaturated fatty acids or alkanol-:"?! amines. Discoloration should be!?! watched for in all the samples thati! i have been put through acceleratedl .:111 stability tests. It is good practice test unperfumed samples Of shampoo along with the perfumed!i !! samples,• If discoloration results, it?.i may be due to the perfume, •vhich.::•! can adversely affect the shampoo other ways as well. Many shampoos are subject t o ' bacterial contamination unless ade• quately preserved. Shelf-testing th':• ': product and waiting for micr6