222 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS plates may be placed face downward on photographic printing paper and prints taken of the patterns, thus giving a permanent record. APPARATUS The apparatus required is simple and consists primarily of a shutter device for controlling the exposure of the plate to the spray. Two general views of this are shown in Figs. I and 2, and a close view of the coated plate in its holder is given in Fig. 3. The shutter is mounted in a grooved upright at the end of a wooden box 18" X 9•" high. Immediately on the far side of the shutter from the box is a holder for the plate (Fig. 3), the height of which may be adjusted to accommodate various sizes of dispensers. It has been found that photographic quarter plates, washed clean of the backing and emulsion, are satisfactory for most types of spray, but if the apparatus were to be re-designed, it would be advantageous to allow space for larger plates, so that a wider spray angle could be accommodated. •1,, with a square The shutter itself consists of a wooden board 18" X hole 5"X 5" cut centrally 6" from the bottom. This hole may be covered to any required extent by a board fixed by bolts running in slots in the main shutter. The shutter is suspended by means of a pin through an eye in its top, and a rod supported by a cross piece at the top of the upright, the lower solid portion of the shutter being between the dispenser and the plate. W•hen the pin is withdrawn the shutter falls under gravity for a distance of about 10" to land on a rubber pad. As the aperture passes through the spray the plate is exposed to it for a fraction of a second. it' is convenient to have an aiming mark on the shutter and to place a scale on the upper surface of the box, indicating the distance of the dispenser from the plate. METHOD (a) Coating the Plates The plates should be thoroughly cleansed before coating, and washing in chromic acid is occasionally advisable. When clean and dry, the plate is mounted horizontally in a clip and coated by the smoke from magnesium ribbon burning beneath it. The thickness of the oxide deposit should be varied to accommodate the type of spray expected, the larger the droplets the thicker the coating needed. Magnesium ribbon -•-" wide, supplied by British Drug Houses Ltd., has been employed, and it has been found that the lengths needed to give coatings on a quarter plate, that were satisfactory for most sprays, were between 12" and 36". The magnesium ribbon should be of good quality, because if any spluttering occurs as it is burning, the coating is liable to be spoilt. The magnesium ribbon is moved by hand,

METHOD FOR DETERMINING SPRAY PATTERNS FROM PRESSURIZED PACKS 223 •?• .....•.• :: ............ ...: Fig. 5. Spray pattern r•orded on coated slide. Figs. 6a and 6b. Two different patterns obtained from the same dispenser.