1200 lOOO 8OO 600 400 200 [19.2] 5% wt/wt 70øC --• 40øC 1.5 hours 10,000 rpm 6.2 ccJmin 0 : elasticity ß : viscosity [ ] : specific volume [9.3] I 3O 20 o lO 8 o deionized artificial water tap water Figure 8. Influence of a hardness of water on the viscoelasticity of the foam from toilet soap. The hardness of the water was 70 ppm (as CaCO•) 1200 1000 800 600 400 2OO 3O 20 •' lO • 0 : elasticity 5% wt/wt ß : viscosity 70 ppm 70øC --• 40øC [ ] : specific volume 1.5 hours 10,000 rpm 6.2 cc/min [•o.71 [9.3] I l 15 : 85 20 : 80 0 0 ratio of coconut oil to tallow Figure 9. Influence of soap composition on the viscoelasticity of the foam from toilet soap

246 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS namic viscosity was not much affected by the specific volume and was approximately 15 to 20 poise. The loss tangent for the foams, a parameter expressing energy dissipation, was calculated to be about 0.3. The interrelation between the viscoelasticity of the foam and the specific volume suggests that the viscoelasticity of soap foam is de- pendent on the diameter of bubble and film thickness. ACKNOWLEDGMENT We would like to acknowledge the continuing guidance and encouragement of Drs. S. Ohta, Director, and T. Mitsui, Associate Director of Shiseido Laboratories, throughout the course of this work. REFERENCES (1) B. Derjaguin, Die elastischen eigenschaften der sch2ume,Kolloid-Z., 64, 1 (1933). (2) B. Derjaguin and E. Obuchov, Untersuchungen tiber die mechanischen eigenschaften disperser systeme und oberfl•ichenschichten: II. die elastischen eigenschaften und dispersit•it der sch•iume, Kolloid-Z., 68, 243 (1934). (3) J. O. Sibree, The viscosity of froth, Trans. Faraday Soc., 30, 325 (1934). (4) G. V. Scott and W. E. Thompson, Measurement of foam consistency, J. Amer. Oil Chem. Soc., 29, 386 (1952). (5) J.J. Bikerman, "Foams," Springer-Verlag, New York (1973).