552 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table II. Summary of actuators and products examined in penetration experiments Orifice diameter Pressures Actuator Type (cm) (kN m -a) Precision 2-piece Swirl chamber 0.045 145-372 PKN-38 Swirl chamber 0.040 152-372 Mechanical break-up 0.075 165-359 The results of the penetration experiments were analysed in the following way. Consider that in time t a total of (No)g of spray approaches the first filter. A fraction Ax of the particles will be removed by the fibres in the first filter, so that the weight collected will be (No)AX, and the total weight passing to the second stage will be (No)(1 -Ax). Assuming that a further fraction Ax is removed at each subsequent stage, the weight penetrating the second filter is: No(1 - Ax) - NoAx(1 - Ax) = No(1 - Ax) • (3) and the weight penetrating filter number y is: N = No(1 - Ax) y. (4) The initial weight, No, is obtained by summing all the weights captured on the individual filters together with that on the back plate, assuming that no material escapes through the gap between the final filter and the back plate. From equation (4) we obtain the penetration at any stage y: N penetration - - (1 - Ax) • (5) No N .'. log - y log (1 - Ax). (6) No N Thus a plot of log •oo against filter number y should be linear and the slope will be a measure of the overall penetration of the spray into the filter.

FACTORS CONTROLLING THE ACTION OF HAIR SPRAYS--Ill 553 RESULTS AND DISCUSSION Velocity measurements Figure 3 shows that the velocity of an aerosol spray varies with the distance from the actuator and with the pressure of the aerosol pack. The results shown are for pack pressures of 152, 221,290 and 359 kN m -• and for a Precision Standard RTBU type actuator. The hair spray formulation consisted of 5.6• crotonic acid/vinyl acetate copolymer in IMS with a product/propellant ratio of 40/60, the propellant being the particular mix- ture of Freon 11 and Freon 12 required to give the desired pressure. 6000 - 4500 3000 1500 o I I © I I o. 5 I0 15 20 25 Distance from actuator (cm) Figure 3. Variation of velocity of aerosol sprays with distance from the actuator. Experimental points: O, 359 kN m-U A, 290 kN m-U X, 221 kN O, 152 kN m -2. Figure 4 shows the velocity profile across the spray cone for the same aerosol packs. These measurements were taken at a distance of 50 mm from the actuator by placing the can on a turntable calibrated in degrees. In each case the aerosol button was initially lined up with the Pitot tube by eye, and the position was taken to be zero degrees. Velocity measurements were then taken on each side of this zero.