MEASUREMENTS ON HUMAN HAIR 395 UPTAKE [ M•"a I G HAIR) Figure 5. Per cent reduction in wet PCL as function of uptake of dodecy]trimethy]- ammonium chloride on bleached hair duced by immersing the bleached hair in 1.0 and .05 g/100 g aqueous solu- tions of the quaternaries for 5 min at room temperature and then rinsing 20 sec as was previously done. The data showed that only very small amounts of these compounds are needed on the hair in order to produce significant effects on combability, and that increasing the uptake beyond these values does not result in additional benefits. It should be kept in mind that the uptake of these compounds by hair is going to be affected by the pH of the medium, the presence of other compounds in solution (especially anionics), and the type of hair. Table VII Effect of Uptake of Quarternary Ammonium Compounds on the Combability of Wet Bleached Hair 1.0 g/100 g solution 5 min .05 g/100 g solution 5 min Uptake Per cent reduc- Uptake Per cent reduc- Compound mg/g Hair tion in PCF mg/g Hair tion in PCF Tetradecyltrimethyl- ammonium chloride 5.9 94. per cent .2 92. per cent Decyltrimethy]- ammonium chloride 9.0 83. per cent 1.5 78. per cent Stearyl dimethylbenzyl- ammonium chloride 2.5 90. per cent .8 90. per cent Benzyltrimethy]- ammonium chloride 4.0 54. per cent .25 50. per cent Distearyl dimethyl- ammonium chloride 3.6 92. per cent .2 9'2. per cent

396 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS DISCUSSION In principle, combability measurements are very simple. In practice, unless great care is taken in the preparation treatment, handling of the swatches, and statistical analysis of the data, the results can lose significance. This is es- pecially true when establishing small differences between products. The main problem arises from the fact that it is difficult to produce a reproducible de- gree of tangling of the swatches prior to the measurements. In our experience, if the method is followed carefully, changes in combability of the order of + 20 per cent can be accurately established without having to measure an im- practically large number of swatches. Changes of this order appear to be close to the lower limit of what can be subjectively noticed by combing swatches by hand. In this method, the before treatment measurements are done on hair which has been cleaned using a detergent solution. This is perfectly justified in test- ing most products because, in reality, shampooing usually precedes the use of most hair care preparations. In the cases where the effects of shampoos are being measured, it could be argued that the starting point should be unclean hair which, in many cases, has better combability than clean hair. This ap- proach, however, will introduce the unnecessary complication of having to ar- bitrarily define and reproducibly simulate dirty hair in the laboratory. Al- though this could be done, we consider that it is justified to start with clean hair and define any effect that a shampoo can have on combability as those effects that can be measured in addition, and beyond the effect produced by shampoos by virtue of just cleaning the hair. In our method, we chose to quantify combability in terms of PCL and ACL. In particular, PCLs are relevant in terms of what is experienced subjectively while combing hair. This is not only because they correspond to the highest forces, but also because, as shown by the combing curves, they occur abruptly. This characteristic of combing forces has been used by Wedderburn and Prall (3) as the basis for developing a method for measuring combability. It is likely, as pointed out by theso authors, that fast short-term fluctuations in the combing forces, i.e., "tangle noise" or "raspiness" (2), are a factor contri- buting to the subjective perception of combing resistance. The inclusion of this effect in the evaluation of combability would be most critical in cases where the effect of two products which produce combing curves of similar PCL, but dissimilar "raspiness" were being compared. This situation, how- ever, has not yet arisen in our experience, and we find that qualitatively PCLs increase or decrease simultaneously with the noise level in the combing curves, i.e., smooth curves give small PCLs, while scratchy curves give large ones. Short-term variations in combing forces thus appear to give similar in- formation to that given by PCL. In the absence of a detailed description of the Wedderburn-Prall method, it is not presently possible to do a fair corn-