400 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS .line, followed by a second, less steep, section. We decided to call the steep .section of the curve the "super foam state". This super foam state is an •'over energised" form of the foam. The length and slope of the super foam curve of a detergent depends upon the amount of work put into the foam. It follows that if equal amounts of work are put into various deter- gent solutions, the longer the life of the super foam and the steeper the gradient of its slope, the easier it is to generate that particular foam. The super foam does not contribute to the cleansing or other useful properties of the foam, but the ability to produce a super foam may be essential to achieve the desired rapid collapse and easy rinsing out characteristics, which are expected from shampoo and toothpaste foams. The duration of the super foam state will be discussed further in our light transmission results. The change in loss factor with time of the four shampoo detergent solutions investigated are similar in character. The slopes of the light transmission curves vary in the same way as those of the viscosity differential and show the super foam state. The significance of these results is dis- cussed in connection with the toothpaste results. The highest loss factor for a foam is obtained after 4 minutes' beating, the 2 and 6 minute foams having about the same loss factor. Temperature of detergent solution has only a slight influence on the loss factor of the foam, the 40øC sample is the only one with a significantly lower loss factor. The loss factor results are used to obtain the specific surface of the foam in question by adapting Clark and Blackman's methods. We also measured the specific surface of the foam using photomicrography. The plot of specific surface with loss factor at a given time yielded straight lines (Graph 7) so for a shampoo foam the loss factor expresses the specific surface. Although the character of the four shampoo detergent foams vary considerably, the specific surfaces are similar. M has the highest specific surface, N a poor foamer, also has a surprisingly high specific surface. The variation of specific surface with the age of the foam is shown on Graph 4. The curve is similar to the loss factor curves and is relatively the same for all the four shampoo detergent foams. D and H have similar specific surfaces and C has the lowest, but the rate of the breakdown of the foam is slow. The growth and collapse of the individual bubbles have also been followed. The larger bubbles increase in size and the smaller ones decrease until they disappear altogether. Examples of these are given in the toothpaste section. The variation in the loss factor and in the specific surface of the foams is surprisingly small, but these differences are very significant. To achieve more diverse results, we would require either liquid with very little air

TECHNIQUES OF FOAM MEASUREMENT 401 present, which is not really a foam, or foams with very large bubbles, which are not encountered in shampoo practice. GRAPH 4 PLOT OF SPECIFIC SURFACE V/S AGEOF FOAM IN MINUTES 2 M H N C Time minutes 1 4 8 1 4 8 1 4 8 1 4 8 « 0.40 -- -- 0.85 -- -- 1-12 -- -- 1-15 -- -- 1 1.05 0.30 0.27 1.77 0.52 0.37 1-88 1.18 0.40 1.95 0.42 0.40 1« 1.36 -- -- 2-08 -- -- 2.10 -- -- 2.25 -- -- 2 1.51 0.68 0.60 2.28 1.00 0.87 2.17 1.62 0.88 2-40 0.95 0.85 2• -- __ __ 2.37 -- __ 2.25 __ __ 2.42 __ __ 3 1.70 0.86 0.88 2.42 1.27 1.20 2.30 1.78 1.10 2.50 1.20 1.02 4 1.76 1.04 1-05 2.48 1.48 1-37 2.38 1.88 1.35 2.55 1.35 1,18 5 1.81 1.12 1.22 2.55 1.58 1.50 2-40 1.98 1.45 2.60 1.48 1.30 6 1.86 1-22 1.30 2.58 1.68 1.60 2.43 2.05 1.55 2.65 1.52 1.38 8 -- 1-31 1.38 -- 1.78 1.72 -- 2.15 1.68 -- 1.68 1.48 10 -- 1.39 1.48 -- 1-85 1.78 -- 2.20 1.75 -- 1.75 1.62 70 • • I • AGE OF FOAM IN UlNUTE5 The rate of draining of the four shampoo detergent solutions was studied after 1, 4 and 8 minutes. All the 1 minute samples drained after 6 minutes, as is shown in Table 2. Table 2 Draining of Mother Liquor from Shampoo Foam.