478 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS the pigment concentration, and F(R) a function of the reflectance. In the Kubelka Munk form of this equation F(R)- 2• and equals the ratio K/S where K is the coefficient of absorption and S is the coefficient of scatter, of the system being measured. I 000 O.lOO o,o1ø• io Control I Control 2 Moritz Popenmeier I'00 Pigre. concentration, % I0'00 Figure 6 Logarithmic plot of ]•/S4o0 v. pigment concentration% (l-R) 2 Thus AC-- 2• --K/S where R is measured at a specific wavelength. It follows that a logarithmic plot of concentration against K/S should give a straight line, with a slope of 45 ø. In practice, hoxvever, it is frequently found that the slope is 37 ø .

'rile DISPERSION OF PIGMENTS INTO DRY POWDER BASE 479 The data given in Tables II are plotted for the four trials at four wavelengths in Figs. 6-9, whilst Table IV shows the angles of the slopes obtained. 1,00• O.lO( 00lO0-10 1,00 IO.00 Pigm. concentration, % Figure 7 Logarithmic plot of I•/S500 v. pigment concentration Table IV Slopes of log I•/S vs. log concentration plots I 600 nm 700 nm Wavelength 400 nm 500 nm Control 1 39 ø 40.5 ø ] 39.5 ø 37 ø Control 2 42.5 ø 41.5 ø I 43.25 ø 43 ø Moritz 40.5 ø 41.25 ø [ 40.75 ø 40.5 Papenmeier 39.5 ø 39 ø I 40.25 ø 39 ø