410 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS sweepings in the laboratory. I am afraid we have, as yet, not made foams from saliva because we do not have a sufficiently good synthetic saliva mixture. We hope to have one because we feel that by keeping our experi- ments as near as possible to user conditions and user requirements, we shall obtain very valuable results. The generation of the foam is the crux of the whole technique. If the generation is no good, then all these results and all the test results can be scrapped. If you care to think that when you shampoo your hair, you have your hand, which is a large area, and the hair, which is an even larger surface area. They rub past each other incorporating air. I feel that the beating of the Mixmaster is similar in character to that. And we have proved this, by taking foam from hair which was being shampooed and determining its viscosity, volume, and other properties. We found that our Mixmaster at 700 revs. per min. and after three minutes of beating, gives a foam with a similar viscosity to that obtained when hair is shampooed for 90 seconds. Having established beyond doubt that our Mixmaster produces a similar type and a similar class of foam although it is about half as slow as in practice, we have gone ahead. The techniques are extremely simple, and easy to use, and they give useful and accurate results. One point about the viscosity results, they are expressed in absolute units. At first we did not expect that we would be able to achieve this but numerous standardisations and cross-standardisations with known oils and other materials, supported it and we can assume that we are in fact getting absolute results. Since the paper was prepared, we have done a lot on shampoo soils, and we are doing two-stage shampooing in our laboratory by using salon sweep- ings. Our techniques are as follows: We are wetting the hair first with water, just as if you were washing your hair and we carry out a two-stage shampoo, and a rinse after each shampooing. We collect water from it, and check the amount of dirt and soil which we get out and it is very much the same or very nearly the same as for an average head. This emphasises that our work is always parallel with practical usage conditions. We found from our experi- ments that petrol-ether soluble soils, which includes the greases, do not affect the foam properties very much. This is rather surprising, and perhaps many people might disbelieve it. The material which affects the foaming power and the power to produce foam at all are the water solubles. We also have the insoluble grit and dirt which simply increases the time for the shampoo to reach its optimum state. In my paper there are these optimum states in viscosity and foam volume after four minutes or six minutes. The presence of grit makes this eight to ten minutes, depending on the amount present. In the paper I say that we do not possess a technique for foam breaking.

TECHNIQUES OF FOAM MEASUREMENT 411 In the meantime, we found a machine called Struers automatic dispenser. Its main use is for biological and biochemical work to dispense a known volume of liquid at a fairly strong pressure and we have put it to use in foam breaking. We generate our foam in the way described, and put a known volume into a glass cylinder which has drainage at the bottom. This is sprayed with water in units of 5 ml at about 3 seconds' intervals to allow the water to drain away. We count the number of sprays to break the foam and we find it gives very satisfactory results. Table 6 Number of injections to break foam Detergent applied to hair Detergent Unsoiled 1st Application 2nd Application M 19 16 20 H 22 18 17 N 23 8 20 C 27 25 23 I feel certain that you realise how important it is to know whether a shampoo will wash away quickly or whether it will take half an hour to wash it out. To achieve a figure of (1) no foam would be present at all even a figure of 8 is an extremely weak foam. With the unsoiled detergent we find that M is easiest to rinse and then H, N and C. If we used C as a shampoo we would be having quite a time to rinse it away. After we used a shampoo and wash in the laboratory we checked our foam again and there was quite a difference from N. The foam produced practically collapsed on the spot. This tells us that it is very easy to wash out, in fact it is dangerously easy and therefore not very good. The foam from C is no good either because it takes many injections and hence a lot of washing out but H and M are the best. The second shampooing in most cases is very nearly the same as the unsoiled, excepting M which shows that the second shampooing is in effect more difficult to wash out than the first one or the unsoiled shampoo. This technique is still in its infancy and we do not have very definite results, except these few on the effect of soil. We have made a film of foam breaking-down, and although this is not terribly exciting as far as movies go, we do learn a lot from it. Besides the obvious ones such as the particle size and the film thickness we also see the mechanism of the breakdown, the formation of the large bubbles, the bursting and in fact one can see the whole structure altering in front of one's eyes. The sequence of the events is illustrated by Figures 5-10.