FACTORS CONTROLLING THE ACTION OF HAIR SPRAYS--I 511 ß 5 •0 /7r (rnm) Figure 6. Variation of capillary rise with reservoir height for commercial hair spray resins in ethanol solution. +, Resin E X, Resin D O, Resin B A, ETCH O, Resin C. The capillary pores within a fibrous system such as a bundle of fibres differ markedly from the cylindrical tube considered above. The channels formed by the interfibre spaces are not cylindrical and often are not closed at the sides and hence link up with other channels. Minor et al have shown, however, that the channels may be considered analogous to a series of tubes, and their size can be expressed by an 'equiva- lent radius' (17). The capillary flow of various organic liquids in textiles

512 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS was shown by these authors to follow the relationship S"= kt, derivable from the Washburn equation (17, 18). Since T, r, 0 and •1 have fixed values for a given liquid/fibre system, equation (1) may be simplified to: dS k dt S (2) which can then be integrated to give: S •' = k't. (3) In the present study the spreading of hair spray resin solutions was compared with this equation in an attempt to define the factors which control the rate of spreading. Experimental A small bundle of about 80 blonde hair fibres was formed into a cylin- drical switch about 15 cm long. The ends of the switch were set with Araldite resin and the completed switch mounted in a frame as shown in Fig. 7. The frame held the fibres taut by means of a tensioning spring attached to one end of the switch. The fibres in the bundle were kept roughly parallel. The switch was not twisted as this was found to give a much tighter packing of the fibres with a consequent decrease in the rate of spreading this very slow rate made the experiments unnecessarily long and furthermore the looser and parallel fibre packing corresponded more closely to hair under natural conditions. The fibre bundle was supported vertically and the lower end immersed in the liquid under test to a depth of about 1 cm. Measurements of the height of rise at various times were made for a series of solutions of commercial hair spray resins in ethanol. The concentration of resin was 5•o w/w in each solution and these were coloured by the addition of 0.5•o of Sudan Black B. The dye facilitated observation of the liquid front within the fibre bundle. No precautions were taken to stop evaporation of the solvent from the rising solutions. It was important that the 'equivalent radius' of the switch was not altered from one experiment to the next. The sizes and distribution of the