COSMETIC KNOWLEDGE THROUGH INSTRUMENTAL TECHNIQUES 133 I I I I I I I I I I I I 2 3 4 5 6 7 8 9 10 11 12 13 14 15 MICRONS Figure &--Spectra of O-2162 and Tween 80 run differentially. ,4 = base line Tween 80 versus Tween 80, B = 0.25% G-2162 in Tween 80 versus Tween 80, C = 0.5% G-2162 in Tween 80 versus Tween 80. All solutions were 5% by weight in chloroform. The spectra were obtained on a double-beam spectrophotometer. graphic column, can be characterized by their resolving powers for a stand- ard mixture. Needless to say, there are much more direct ways of analyzing detergents and surfactants, but it serves as a useful illustration of how man should direct the machine, and not the reverse. INFRARED SPECTROMETER If you looked through the last ten years Of THE JOUR•r^L OF THE SOCIETY or COSMETIC CHEMISTS and of the PROCEEDINGS OF THE SCIENTIFIC SECTION OF THE TOILET GOODS ASSOCIATION, you would find that papers on the use of the infrared spectrometer outnumbered those on any other instrumental technique, even though the first reported use of this instrument in these journals does not appear until December, 1952 (5). It would seem, there- fore, that the cosmetic industry was about ten years behind the chemical industry in its acceptance of and use of this machine (6). The inability of the machine to measure directly those properties of a cosmetic product, which can be tied to consumer acceptance of the product, may have been a factor in this delay. However, the enormous benefits to be derived in control work, both of raw material and of finished product and in analysis of competitive products are surely appreciated today. Figure 5 shows the infrared spectra of G-2162 (Atlas Powder Company's polyoxyethylene propylene glycol monostearate) and Tween 80 (Atlas Powder Company's polyoxyethylene sorbitan monooleate). There are some differences, in spite of the over-all similarity of the spectra, which might be used to look for a small percentage of one in the other. For the

134 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS best chance of detecting minor traces of one in the other, the unknown is run differentially against the pure known. (A double-beam machine is needed for this.) If they are identical, the absorptions in both beams cancel out and a straight line is obtained. If not, the difference is readily seen. Fig- ure 6 shows the differences which can be obtained when run differentially. CONSTANT RATE or ELONGATION TESTER A machine which has been of tremendous use in the research program on hair and other fibers is the Constant Rate of Elongation Tester--called the C. E. Tester for short. The instrument was made by G. F. Bush As- sociates (Princeton, N.J.) to meet the requirements of Evans Research and Development Corporation. An important feature is the arrangement for complete immersion of the sample under test. The fibers can be stretched anywhere between 50 per cent per minute and 1.25 per cent per minute, by varying the sample size and elevator speed. The strain gauge can be one giving 0.5 gin. full scale or bigger ones, up to 2.5 kg. full scale, can be used. Usually tensile forces are measured, but the machine is easily adapted to a variety of techniques, such as cycling, cutting or compression. One of the most useful of the results given by this machine is the 20 per cent Index. A 12-hair strand is stretched 20 per cent in water. It is then 200 150 lOO 50 PermanenHairWaved I I , I lO 15 20 EXTENSION (%) Figure 7.--Typical hysteresis curves for untreated human hair and permanently waved human hair.