290 JOURNAL OF THE SOCIETY O17 COSMETIC CHEMISTS person is used as the subject for the two compounds being compared. Thus, it is more time-consuming as it requires the technician, equipped with sterile rubber gloves, to wash each hand of the subject individu- ally. As advantages, however, by using the same skin for the two materials, it tends to eliminate what might be an error due to two individuals possessing different types of skin which would react in a different manner to the two materials being compared and to the degerming process. The re- mainder of the test as to plating of the wash water for bacterial counts, interpreting the data, etc., remains the same. S LrMMA RY An in vivo method for determining the skin-degerming efficacy of the product hexachlorophene when in- corporated in soap has been pre- sented here in detail, together with a brief discussion of some of its variables and reasons for certain phases of the technique. BIBLIOGRAPHY (1) Price, P. B., "New Studies in Surgical Bacteriology and Surgical Technique with Special Reference to Disinfection of Skin," •t../lm. Meal../lssoc., 111, 1993- 1996 (1938). Price, P. B., "The Bacteriology of Nor- mal Skin a New Quantitative Test Applied to a Study of the Bacterial Flora and the Disinfectant Action of Mechanical Cleansing," y. Infect. Dis., 63, 301-318 (1938). (2) Traub, E. F., Newhall, C. A., and Fuller, R. J., "Studies on the Value of a New Compound Used in Soap to Reduce the Bacterial Flora of the Human Skin," Surg. Gynecol. Obstet., 79, 205-216 (1944). (3) Unpublished data, personal communica- tion. SPECTROPHOTOMETRY IN THE ANALYSIS OF COS- METIC PRODUCTS* By G. ROB•.RT CLARK Chief, Division of Cosmetics, Food and Drug •ldministration, Federal Security •lgency, tl7ashington, D.C. THE PAST ten or twelve ' years have seen a rapid growth in the industries producing instru- ments for scientific investigation. A considerable portion of the ex- pansion has been in production of spectrophotometric devices. Ac- * Presented at the May 18, 1951, Meeting, New York City. curate automatic recording spectro- photometers have been produced as standard items, some of these are, or were until recently, available from stock. The literature describing appli- cations of these instruments has been increasing at a tremendous rate. It appears that another dec- ade or so will see the spectro-

SPECTROPHOTOMETRY IN ANALYSIS OF COSMETIC PRODUCTS 291 photometers classed along with chemical balances as fundamental laboratory equipmen t. It is customary to regard spectro- photometry as divided into three parts, according to the wavelength of the light used. These are the ultraviolet, visible, and infrared regions of the spectrum. More or less arbitrarily, the divisions are for practical purposes set at below 400 m• for ultraviolet, 400-750 m• for the visible, and 750 mu on up for the infrared. VISIBLE REGION 400--750 MU The visible region of the spectrum is of limited usefulness in that only colored substances have absorption in this range. In the cosmetic industry the principal interest would be in color matching, either by transmitted or reflected light, and in the analysis and standardization of dyes and pigments. I shall not spend much time discussing these applications, except to point out that for such purposes the spectro- photometer is invaluable. UL.R^vIOLE. REGIO• BELOW 400 MU In the ultraviolet region, all aro- matic compounds show character- istic absorption. When the entire absorption spectrum is obtained and plotted in the usual manner, i.e., absorbency vx. wavelength, the curve obtained will be char- acteristic of the particular com- pound. An exception is stereo- isomers, in which case both com- pounds show the same absorption. Beside aromatic compounds, mole- cules with two or more conjugated double bonds absorb ultraviolet radiation above 230 mu. Examples are fatty acids with conjugated double bonds, aldehydes or ketones with double bond conjugated with carbonyl, such as aceto acetic esters or ascorbic acid. A considerable number of in- organic salts also absorb ultra- violet above 210 mu. Below 210 mu--out of the range of most commercial instruments-- isolated double bonds, isolated C=O groups, and some other groups show specific absorption. Since practically all compounds absorbing in this region follow Beer's Law over wide ranges of con- centrations, ultraviolet absorption spectra can be used for quantitative as well as qualitative analyses. All that is necessary is to determine the absorption spectrum of a sample of known identity and purity and to compare this with the spectrum of the unknown. INFRARED REGION ABOVE 0.75 In the infrared, 0.75 to 2 u, the so-called "overtone" region, almost all organic compounds show ab- sorption. While this region is of interest to theoretical chemists in investigating fundamental frequen- cies, bond energies, etc., the quali- tative and quantitative applications are quite few. The H20 absorption at about 1.5 u is sometimes used to detect traces of H,.O in refrigerating gases, alcohol, etc. In the region 2 to 40 u, all com- pounds except strictly non-polar