94 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 1. Soap residues after washing as revealed by fluorescein fluorescence. Samples N and P demonstrated average rinsability, with all the other products tested showing slightly above or below average rinsability. DISCUSSION In comparing the two methods, the spectroscopic method is simpler, does not require special photographic equipment, and is substantially more quantitative than the photo-

SOAP AND DETERGENT RINSABILITY 95 Figure 2. Soap residues after washing as revealed by fluorescein fluorescence. graphic method. The photographic method exploits well the impact of direct visual comparison. The results of both methods are comparable as shown by a linear regression analysis of the two methods which yielded a correlation coefficient of 0.952, indicating an excellent correlation between the two methods. The spectroscopic method was designed to quantify the dye residue rather than simply visually ranking it. Since many soap and detergent bars contain antioxidants, bright-

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