646 R. W. Pengilly and J. A. Keiner The effective range of the light scattering system was 1.7-14 gm and two measure- ment ranges of the optical array system were employed (3-3-50 and 20-300 gin). Each range was subdivided into fifteen separate size channels, from which number/size channel information was obtained. The particle size distributions were recorded by spraying the aerosol for five seconds into the appropriate probes. With the actuator orifice and the axis of the laser beam in one horizontal plane, distances were selected at 28 and 48 cm from the actuator orifice to the laser beam axis. This was because of experimental convenience and because the distributions could be expected to exhibit significant differences due to evaporation of the volatile components of the particles. The prevailing conditions of measurement were 20øC and 50 •o Relative Humidity. Two model aerosol formulations were selected for this work, based on 15/85 and 35/65 product/propellant ratios. The formulations are detailed in Table II. The valve/ actuator systems selected are listed in Table III these were selected to include a range of valve/actuator variables used in aerosol formulation studies. These variables included the size of the valve housing orifice and the presence or absence of a vapour phase tap in the valve. The actuators employed were a mechanical break-up (four-channel swirl chamber) system and a standard 0.015-inch spray orifice button. The particle sizing systems were calibrated with monodisperse polystyrene latices (0.5-2 gm diameter) and with glass beads (50-300 gm diameter). Table II. Aerosol formulations (a) 35/65 Product/Propellant System •o w/w 'Resyn' 28-2930 * 1'10 Amino-methyl propanediol '[' 0'11 Ethanol 33'79 Fluorotrichloromethane (3) :l: 42.20 Dichlorodifluoromethane (3) :l: 22.80 lOO.OO (b) 15/85 Product/Propellant System •oW/W 'Resyn' 28-2930 * 1.10 Amino-methyl propanediol •' 0.11 Ethanol 13.79 Fluorotrichloromethane :[: 55.25 Dichlorodifluoromethane/ 29.75 100.00 * National Starch and Resin Corporation Inc. '1' British Drug Houses Laboratory Reagent. :l: Imperial Chemical Industries (Mond Division).

Figure 3. The complete measuring system. Facing page 646