870 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 1. Assembled Cascade Impactor fitted with sampling chamber Fluorometric Method A fluorometric method was also used to determine quantitatively the amount of residue deposited on each slide. A Turner Fluorometer,* Model 111, was fitted with the proper primary and secondary filters, de- pending upon the nature of the fluorescent dye used as a tracer. Each of the slides from the Cascade Impactor was thoroughly washed with 5 ml of anhydrous ethanol in a 10-ml beaker in order to dissolve the residue. The sample was then transferred to a 5-ml Pyrex glass cuvette and its per cent fluorescence determined. This method was used throughout this study. Selection o[ Tracer Dye Several different fluorescent compounds were investigated. Prelim- inary studies indicated that Blancophor AW High Concn.* might be use- ful for this purpose. Chemically, this compound is 4-methyl-7-dimethyl aminocoumarin. * G. K. Turner Associates, Inc., Palo Alto, Calif. • GAF Corporation, Dyestuff and Chemical Division, New York.

PARTICLE SIZE DETERMINATION 871 OH3 CH3-- N••H:••0 Peak absorption occurs at approximately g66 m/• (long-wave UV range) while peak readmission o[ visible light occurs at between 465 and 470 m/x although there may be some variation depending' upon the sub- strate. Solutions of Blancophor were prepared in absolute ethanol.* A solution containing 0.50% by weight o[ Blancophor was diluted with ab- solute ethanol in order to produce concentrations in the range o[ 0 to 0.5% by weight. The fiuorometer was fitted with the filter combination shown in Table I. Five milliliters of each dilution was placed in a cu- vette and the per cent fluorescence was read. These results are shown in Table I and Fig. 2 and represent the average o[ three determinations. The above procedure was repeated using dilutions o[ Blancophor in the range o[ 0 to 0.05% by weight of solution using absolute ethanol as the solvent. These results are shown in Table II and Fig'. 2 and repre- sent the average o[ three determinations. * Similar dilutions were prepared using SDA 40 anhyd. and no change in fluorescence was noted using the filter combinations indicated. Table I Fluorescence of Blancophor AW High Concn. Solutions Blancophor Solution Fluorescence Readinga (wt %) (%) 0.50 76 0.45 75 0.40 74 0.35 70 0.30 68 O.25 65 0.20 61 0.15 54 0.10 47 0.05 36 0. 025 24 0.0125 15 0. 0063 12 0.0031 7 0.0016 4 0 0 ', Primary filter, (47B q- 2A) secondary filter, (2A -- 12 or 15 -b 1% neutral filter) range, 10X.