SENSORY FIRMNESS AND VISCOUSNESS ,491 Scott-Blair and Coppen (4, 5) reported that the firmness was considered to be easier to distinguish than viscousness. From our study it was rioted that two areas for the discrimination thresholds of cosmetic creams were present, one where firmness was easier to discriminate than viscousness in the range of high hardness and viscosity (which corresponded well to the 'result ob- tained by Scott-Blair and Coppen) and the other, where the relationship was vice versa in the range of low hardness and viscosity. In order to compare the hardness with the elasticity, the elasticity of the same samples used in this study was also measured •vith a parallel plate plas- tometer. The correlation coefficient bet•veen the hardness and the elasticity vas found to be very high (r = 0.997) as seen in Fig. 9. Therefore, it is con- sidered that the hardness of the samples used in this study did correspond to the elasticity. As indicated above, our discrimination thresholds •vere calculated from the data obtained by judging correctness or incorrectness for all possible combi- nations of the two obtained from the data of the ranking method, vhich dif- fered apparently from the ordinary differential threshold. Aceord:ngly. an analysis was carried out by applying the constant method for converting our data to ordinary differential threshold (6). The calculated data are sho•vn in 97 Y= 0.73x102X +0.06x104 i i i {g/crn2) x102 Hardness Figure 9. Relation between hardness and elasticity in the case of cream base substances

49g JOURNAL OF THE SOCIETY OF COSMETIC CItEMISTS ,,, ,,,40 lO Discrimination Threshold ........ Differential Threshold aP=80•o 101 102 103 10" (g/cm 2 ) Hardness Figure 10. Comparison between discrhnination threshold and differential threshold for firmness of cream base substances in relation to hardness • 40 ,-½5 30 :• •. 20 10 • Discrimination Threshold ..... Differential Threshold '4p=80• i 10 2 10 3 10 4 cps Viscosity Figure ii. Comparison between discrimination threshold and differential threshold for viscousness of cream base substances in relation to viscosity