242 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS •1 = SR = SM (287/Td) [8] = Sk (8•/2•r 2) (T2/Td) where T is the period of free oscillation and is given by T = 2•' %/•/k [9] M and k were determined from eq [9] by measuring T at various weights. The shape factor S was calculated from eq [8] by using the experimental values obtained on a stan- dard viscosity sample (Showa Petroleum Co., JS 2000). We should point out that such an indirect determination of S involves the risk of allow- ing an error in measurement. The. reason for having to adopt the indirect way to de- termine S can be summarized as follows. A large volume of foam sample was required for the measurement in order to satisfy the condition of the flow between parallel plates under which S is theoretically obtained, since foam is generally a coarse disperse system. On the other hand, if such a large volume of foam is used in measurement, it is unavoidable that the foam becomes more heterogeneous in film thickness because of drainage in the film. This problem is expected to be solved by devising an entirely new type foam-generator providing a homogeneous foam to a measuring vessel where the condition of the flow between parallel plates is taken into consideration it is an im- portant subject for further study. 1200 1000 800 600 400 200 o : elasticity 70 ppm 70øC --- 40øC ß : viscosity 1.5 hours ( ]: specific volume 6.2 cc/min ] 0•000 rpm (10.5] • [8.9] -.o.... (8.2) -30 -20 o_ ,,,i,- -10 u • I • • • 0 O0 1 2 3 4 5 soap concentration, % wt/wt Figure 5. Dependence of the viscoelasticity of the foam on the toilet soap concentration. The specific volume of the foam sample is designated in brackets

ViSCOELASTIC MEASUREMENT ON FOAM 243 1200 lOOO 800 600 400 200 o : elasticity 5 % wt/wt 70 ppm ß : viscosity 70Oc_•40oc [ ]: specific volume 1.5 hours 5.4 cc/min (24.4] 30 5000 7500 10000 12500 rotational frequency, rpm Figure 6. Effect of rotational frequency of the foam-generator on the viscoelasticity of the soap foam ob- tained from a 5 % (wt/wt) toilet soap aqueous solution. The specific volume of the foam sample is designated in brackets APPLICATION OF THE DEVELOPED SYSTEM TO THE MEASUREMENT ON THE FOAM FROM TOILET SOAP A commercial toilet soap was used. A toilet soap aqueous solution was prepared by dissolving the toilet soap at 70øC in the artificial tap water described above. After disso- lution, the solution was cooled to 40øC in a bath containing iced water. The solution was then allowed to stand for 1.5 hr at 40øC in the foam-generator before testing. Measurements were conducted at about 2.5 Hz on the foam at 40øC. The dependence of the viscoelastic toodull of foam on soap concentration is shown in Figure 5. The foams were prepared under such condition that a flow rate of solution to the foam-generator is 6.2 cma/min and a rotational frequency is 10,000 rpm. A specific volume (cma/g) of a foam sample is designated in brackets. The elasticity decreased with increasing soap concentration, whereas the viscosity was not much affected by the soap concentration. In Figures 6 and 7, the influence of a foaming condition on the viscoelastic moduli of the foam is shown. The soap concentration was 5% (wt/wt). The effect of a rotational frequency on the viscoelastic toodull of the foam is shown in Figure 6. The elasticity decreased from about 850 to 500 dynes/cm 2 as the rotational frequency increased, while the viscosity increased slightly. The effect of a flow rate of solution on the vis- coelastic moduli of the foam is shown in Figure 7. The elasticity increased from about