RHEOI.OGICAL MEASUREMENTS IN THE COSMETIC INDUSTRY 89 REFERENCES (1) Walshe, F. M. R., Brain, 65, 48 (1942). (2) Weddell, G., "Cutaneous Sensibility," in "Modern Trends in Dermatology," by R. M. B. Mackenna, 2nd Series, New York, Paul B. Hoeher, Inc. (1954), pp. 48-56. (3) Weddell, G.., Pallie, W., and Palmer, Elizabeth, •uart. •. Microbial. Sci., 95, 483 (1954). (4) Weddell, G., Palmer, Elizabeth, and Pallie, W., Biol. Revs. Cambridge Phil. Soc., 30, 159 (1955). (5) Winkelmann, R. K., "Nerve Endings in Normal and Pathologic Skin," Springfield, Ill., Charles C Thomas (1960). (6) Winkelmann, R. K., Proc. Staff Meetings Mayo Clinic, 34, (Jan. 21), 39 (1959). (7) Winkelmann, R. K., y. Comp. Neurol., 109, 221 (1958). (8) Weddell, G., y. Atnat., 77, 49 (1942). (9) Winkelmann, R. K., •inn. N.Y. Atcad. Sci., 83, 400 (1959). (10) Winkelmann, R. K., and Schmit, R. W., •i.M..4. •irch. Dermatol., 80, 543 (1959). (11) Montagna, William, and Ellis, R. A., y. Invest. Dermatol., 29, 151 (1957). (12) Winkelmann, R. K., •i.M.•i. •irch. Dermatol., 76, 225 (1957). (13) Winkelmann, R. K., "Similarities in Sensory End-Organs," read at the Providence Seminar on the Skin, Providence, R. I., January 30, 1959, in press. (14) Winkelmann, R. K., y. Invest. Dermatol., 29, 347 (1957). (15) Bishop, G. H., Physiol. Revs., 26, 77 (1946). (16) Wall, P. D., and Cronly-Dillon, J. R., •i.M.•i. •irch. Neurol., 2, 365 (1960). (17) Weddell, G., Sinclair, D.C., and Feindel, W. H., y. Neurophysiol., 11, 99 (1948). (18) Shelley, W. B., and Arthur, R. P., •i.M.•i. •irch. Dermatol., 76, 296 (1957). (19) Hurley, H. J., and Koelle, G. B., y. Invest. Dermatol., 31, 243 (1958). (20) Winkelmann, R. K., Ibid., 27, 273 (1956). (21) Winkelmann, R. K., Cancer, 13, 626 (1960). RHEOLOGICAL MEASUREMENTS IN THE COSMETIC INDUSTRY By R. H. MARRIOTT, D.Sc.* Presented September ZS-Z6, Z960, Seminar, Chicago, Ill. IT IS AS NEAP. a truth as does not matter to say that the usefulness of products and their appreciation by people involves the physical-chemical properties of matter. In the hands of the user the differentiation is made through the senses of touch, sight, hearing, taste and smell, all of which, singly or together, are involved when cosmetics are used. The cream in the pot is looked at, smelled, touched and often tasted. Hearing is not normally employed but this sense can be of value under dynamic conditions. The scroop of well-washed wet hair is an example of a physical test of the efficiency of a shampoo which can be detected by the ear. In use, cosmetic products are evaluated generally by touch. A stroke of the finger tells of rigidity, thixotropy, viscosity, smoothness and texture in general. Coupled with a seeing eye, simply spreading the preparation on the skin can cause the brain to appreciate uniformity, coherence, absorption and many of the features of a thin film--it may be shiny, be dull, or matt, * Consulting Chemist, London N. 20, England.

90 JOURNAL O17 THE SOCIETY OF COSMETIC CHEMISTS or have a pearly lustre. Such a procedure involves some motion or flow and falls within the ambit of rheology. The assessment so obtained is qualitative and lacking the precision of scientific measurement, the con- clusions are generally ambiguous. It is not the purpose of this lecture to disserrate on theology in the aca- demic fashion. Reference may be made to de Waele (1) who gave a practical exposition and described various instruments, penetrometer, plastometer, flow meter and thixometer. He rightly stressed that such mechanical de- vices give comparative values and that the properties measured depend on the quantitative as well as the structural composition. [See also the paper by J. pryce-Jones (2).] Scarbrough.(3) paid particular attention to pastes and showed that yield value was reduced by surface tension-reducing substances and vice versa. Meyer and Cohen (4), using the Brookfield viscometer, related the meas- urements to the suspending power of a variety of hydrophilic colloids. It should be noted that these authors employed low concentrations of solids. Adler (5) gave a simple and clear outline of the rheology of NewtonJan plastic and pseudo-plastic systems, such as arise in the cosmetic industry. More recently, Heinrich and Clements (6), having been fortunate in possessing a self-recording Ferranti-Shirley instrument, give a comprehen- sive series of graphs and claim that the instrument will enable novel formu- lations to be made with new and hitherto unsuspected cosmetic properties. What is important is that the graphs are in terms of instrument readings and not calculated to C.G.S. units. It would seem that for industrial usage, and bearing in mind that rhe- ological measurements are essentially dynamic, the experimental condi- tions should be such that the results are simply figures which can be used comparatively. The reason for this is because the appreciation of these properties is through the human mind and no mechanical device has yet been found which can assay the properties of matter in terms which can be applied to the reactions of the human mind. This aspect of rheology is well covered by Scott Blair (7) in his book "Survey of General and Applied Rheology." Additionally, much valuable information will be found in the report of the Symposium on "Texture in Foods" (8). It is not, of course, denied that academic experimental theology is of great value. Such work is necessary if genuine progress is to be made. One has, however, to differentiate between rheology in pure research and theology as a means of controlling a practical operation. I think everyone appreciates that if every rheological problem in our industry were to be tackled on academic lines, not only would it call for a huge staff and a mas- sive investment in apparatus but it would seriously delay the rate of produc- tion of a product. It is the aim, therefore, of this paper to indicate how to make quick