742 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS This expression would be simpler if h2 could be neglected and if the ratio h/R is very small this is possible. Table I shows the percentage errors which would arise in the estimation of a2 and a3 if the original data are values of h, and h2 is neglected. Table I Percentage errors in the square and cube of the radius of the circle of contact, a, (neglecting h 2 in Equation 3) as a function of P, the ratio of htoR. P Percentage error in a 2 0.01 -0.503 0.05 -2.56 O. 10 I -5.26 Percentage error in a 3 -0.713 -3.84 -7.97 The proposed method has two slight disadvantages- (i) Dependence of the creep function on a3 makes the method more insensitive at long times than more conventional creep methods. (ii) Creep recovery is difficult to carry out. The method is, however, very simple in practice and would probably give plenty of information for quality control. The great convenience of being able to test the material in the container is an attractive feature of the method. (Received: 27th May 1968) REFERENCES (1) Barry, B. W. and Shotton, E. J. Pharm. Pharmacol 19, 110S (1967). (2) McKennell, R. Proc. 2rid Int. Cong. Rheol., 350 (1954). (3) McKennell, R. Analyt. Chem., 9.8, 1710 (1956). (4) McKennell, R. The Instrument Manual, 3rd edn. 318. (1960). (United Trade Press, London.) (5) Van Wazer, J. R., Lyons, J. W., Kim, I(. Y. and Colwell, R. E. Viscosity and Flow Measurement. A Laboratory Handbook of Rheology, 122 (1963). (Interscience, New York.) (6) Barry, B. W. and Shotton, E. J. Pharm. Pharmacol 9.0, 167 (1968). (7) Barry, B. W. Ph.D. thesis. 117 (1967). (University of London). (8) Burgess, J. M. and Scott Blair, G. W. Proc. Intern. Rheol. Cong. V, 1-65 (1948). (9) Van Wazer, J. R., Lyons, J. \V., Kim, K. Y. and Colwell, R. E. Viscosity and Flow Measurements. 21 Laboratory Handbook of Rheology, 77 (1963). (Interscience, New York). (10) Scott Blair, G. x•V. 21 Survey of General and Applied Rheology 2nd edn. 76 (1949). (Pitman and Sons Ltd., London). (11) Axon, A. J. Pharm. Pharmacol. O, 830 (1954). (12) Ober, S.S., Vincent, H. C., Simon, D. E. and Frederick, I(. J. J. A•n. Pharm. 21ssoc. Sci. Ed. 47, 667 (1958). {13) Boylan, J. C..[. Pharm. Sci. 55, 710 (1966).

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