390 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS make varifiable or refutable predictions. The techniques discussed assist in predicting short-term emulsion stability, but the practical cosmetic chemist is vitally interested in long-term stability, not minutes or hours, but weeks or months. At present he cannot find out empirically if prophetic judg- ment can be made this would be most valuable. It is appreciated, of course, that such long-term stability may be affected in complex systems by migra- tion of trace impurities to the interface, but could these techniques be of assistance ? THE LECTURER: The techniques I have described could give you the information you require provided the change taking place occurs at the interface. It is my experience that there is no substitute for time and one must therefore be prepared to set up the experiment to last for the required period. It may be that surface chemical techniques will detect changes much earlier than those detected by storage tests on the product. For instance, migration of divalent ions to a surface stabilised by a sodium soap will be manifest as a change in rigidity of fhe interface. TECHNIQUES OF FOAM MEASUREMENT G. E. NEU, B.Sc.* Delivered at the Summer Confere•ce of the Society on 25th August 1960. The physical properties of shampoo and toothpaste foams are character- ised using seven different measurements. These measurements are easy to perform and yield reproducible results. A subjective assessment of the foam is correlated with the measurements described. INTRODUCTION FOAMINC IS of major importance in shampoos and toothpastes, and the nature of the foam may be critical in determining the acceptability of these products. With toothpaste, the volume must be sufficient but controlled, and one of the chief qualities required is easy rinsing away the foam is also important to the flavour which it disperses throughout the mouth to allow maximum contact with the taste buds. The actual requirements of these two products are very different. A shampoo is normally expected to give a thick, creamy, voluminous foam, which is associated by the user with cleansing power and emolliency. Even if a shampoo has excellent cleansing properties and leaves the hair in very good condition afterwards but only provides a small amount of a thick, *Unilever Ltd., Isleworth, Middlesex.

390 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS make varifiable or refutable predictions. The techniques discussed assist in predicting short-term emulsion stability, but the practical cosmetic chemist is vitally interested in long-term stability, not minutes or hours, but weeks or months. At present he cannot find out empirically if prophetic judg- ment can be made this would be most valuable. It is appreciated, of course, that such long-term stability may be affected in complex systems by migra- tion of trace impurities to the interface, but could these techniques be of assistance ? THE LECTURER: The techniques I have described could give you the information you require provided the change taking place occurs at the interface. It is my experience that there is no substitute for time and one must therefore be prepared to set up the experiment to last for the required period. It may be that surface chemical techniques will detect changes much earlier than those detected by storage tests on the product. For instance, migration of divalent ions to a surface stabilised by a sodium soap will be manifest as a change in rigidity of fhe interface. TECHNIQUES OF FOAM MEASUREMENT G. E. NEU, B.Sc.* Delivered at the Summer Confere•ce of the Society on 25th August 1960. The physical properties of shampoo and toothpaste foams are character- ised using seven different measurements. These measurements are easy to perform and yield reproducible results. A subjective assessment of the foam is correlated with the measurements described. INTRODUCTION FOAMINC IS of major importance in shampoos and toothpastes, and the nature of the foam may be critical in determining the acceptability of these products. With toothpaste, the volume must be sufficient but controlled, and one of the chief qualities required is easy rinsing away the foam is also important to the flavour which it disperses throughout the mouth to allow maximum contact with the taste buds. The actual requirements of these two products are very different. A shampoo is normally expected to give a thick, creamy, voluminous foam, which is associated by the user with cleansing power and emolliency. Even if a shampoo has excellent cleansing properties and leaves the hair in very good condition afterwards but only provides a small amount of a thick, *Unilever Ltd., Isleworth, Middlesex.