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b i 10 7i 2b is 30 35P. Welmans, Pharmaz. Ztg. 45, 959 [1900].

In order to confirm and extend earlier work on the colorimetric evaluation of whiteness, different series of white textiles, each of constant reflectance, varying from Y = 96 to Y = 70, are studied. A study of the Ciba-Geigy white scale is also included.Earlier predictions about the shape of the equi-whiteness surfaces in the x, y, Y colour space are confirmed and refined. As a result it is established that our original method used as such (using a diagram in the x, y chromaticity chart) or as adapted jbr numerical computation by Ganz, is applicable to nearly all white textiles, with or without FWAs. Only if shading dyes are used can the colour point trnnsgress the optimum whiteness point corresponding to the reflectance of the material. In such cases it is necessary to use equi-whiteness ellipses around the optimum point, whose position in the chromaticity diagram varies nearly linearly with reflectance. it is also found that catastrophe theory applies to whiteness perception in the vicinity of the optimum whiteness axis in colour space. This means that the whiteness of a given colour in this domain can have a high and a low value, according to circumstances.

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International organisations are studying the standardisation of unsoiled cotton test pieces and methods of using them for the determination of chemical damage and mechanical wear in laundering. Of particular importance is the relation between chemical attack, as measured by viscosity or fluidity changes, and the corresponding strength loss. Study of the literature reveals that the available experimental data are far from complete and that published curves differ. In order to clarify the position, loads of test pieces of two different plain–weave cotton fabrics were laundered up to 35 times, without and with hypochlorite bleach, under different conditions, and an attempt was made to find the breaking strength loss corresponding to a given fluidity increase under identical mechanical conditions.It is concluded that, up to a 20 % strength loss, the relation between strength loss and fluidity increase is a linear one, provided that the severity of the chemical attack remains constant; above this value a curve similar to that of Clibbens and Ridge is found. In practice, however, test pieces are examined after a constant number of launderings, usually 25; consequently, low fluidity values correspond to a slow chemical attack, and high values to a rapid chemical attack. Under these conditions a curve is found that is similar to the Delft curve now under consideration for international standardisation, up toa 20% strength loss; above this value it remains similar to the curve of Clibbens and R idge.