THE RHEOLOGY OF PASTES, SUSPENSIONS AND EMULSIONS '191 the dilatant system, the suspension immediately became sticky. Does the lecturer know whether this change from non-sticky to sticky is associated directly with a change from di!atant to nomdilatant system and is there any suggestion that the degree of stickiness is related to the distance away from the di!atant state ? TI•E LECTURER: From my experience with a good many materials, I should think that this is very probably true. It is a most interesting sugges- tion but I cannot think of any theoretical explanation for it. MR. A. •)E WAEX, E: I should be interested to know the approximate volume ratio solid to liquid in the "dilatant" cornflour/water paste which formed the subject of the demonstration. The point I seek to know is whether the volume concentration corresponds to anything near the cubical or diagonal piling of Osborne Reynolds, i.e. about 50 per cent and 75 per cent respectively. A quasi-di!atant system is formed when highly hydrophilic powders such as ultramarine or the early varieties of titanic oxide pigment are dispersed in a non-polar mineral oil such as liquid paraffin B.P. These represent com- binations having very low physical affinities or degrees of wetting between the phases. At volume concentrations even as low as 5 per cent, marked dilatancy is shown. Such pastes defy consistent rheological measurements as they increase in consistence under shear and become crumbly. They also exhibit the "quicksand" effect of Osborne Reynolds [An Inversion of Ideas as to the Structure of the Universe, Rede lecture (1902) (Cambridge University Press).] when slowly sheared under a palette knife with a backwards and forwards motion. Thus in front of the advancing knife blade the material develops gloss, whilst in retreat of the blade it becomes dull and crumbly. This peculiar property gradually becomes lost on long storage, but can be immediately destroyed by addition of a small amount of dispersing agent. TI•E LECTURER: It appears that there are many cases of apparent dilatancy which occur at concentrations which could not possibly correspond to close packing. The mechanism is still quite a mystery, Ref. Metzher A. B. and Whit!ock M. Trans. Soc. Rheol. 2 239 (1958) and Jobling A. and Roberts J. E., Rheology of Disperse Systems. Ed. Mill, C. C. (1959) (Pergamon Press). MR. T. J. EX, X, IOTT: Does order of stickiness vary with different types of measuring material ? TI•E LECTURER: Yes, Claassens has found an almost exactly reversed order of stickiness to different materials for butter, using a normal pull and a tangential pull respectively. (S. African J. Agricultural Sci. 1 457 (1958): 2 89, 427 (1959) and further papers in press.) Long ago, Russian workers showed that the order of stickiness of different field soils depended on the material from which the mouldboard of the plough was made.

192 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS MODERN TRENDS IN COSMETIC FORMULATION W. W. MYDDLETON, D.Sc. A lecture delivered before the Society on 18th November 1959. Cosmetic chemists have been led to modifications in lormulation by a number o• different routes. Examples are given o• the successful masking or elimination o• undesirable characteristics in otherwise valuable cosmetic ß aw materials. Some commonly accepted ideas on •ormulation are shown to be o• limited validity. Work carried out in biological sciences has given ,an impetus to tissue extract therapy in some quarters with inconclusive results. THERE ARE tWO conventional approaches to a discussion on a topic con- .cerned with cosmetics. The first is to retire to a considerable distance as for example Babylon or Ancient Egypt and to work through the civilisations which have led to our own. The second is to handicap oneself with a number of restrictions in the form of definitions from a reputable dictionary. In the new and unconventional approach I have devised I shall present to you a verbal picture of the subject, Modern Trends in Cosmetic Formulation, as it appears to me. The Cosmetic Formulary appears to me as a flourishing tree with many spreading branches on these branches are to be found healthy developing buds some of which show promise of flowering and coming to fruition and some of becoming in turn new branches. These buds are to me the Modern Trends in Formulation, not all of them will fulfil their early promise some will wither and die and others will be removed by purposeful disbudding, or at a later period be pruned away in the interest of the general symmetry of the tree. My own interest lies not in knowing that So-and-So did Thus and Thus, or that So-and-So made This and That, but in knowing why on earth they did so. It is by understanding how modern trends have developed and taken shape that we shall appreciate and perhaps anticipate for ourselves how in the future newer trends may be planned. The prime mover is planning and it requires co-operative effort the producers and suppliers of raw materials no less than the chemists and technicians of the cosmetic industry are ,concerned in it. For fruitful planning it is essential that there should be a free interchange of ideas and information amongst all concerned, and any