Rating -- 1 2 3 PI, ARLESCENT STRUCTURI'•S Xo pearleseence or iridescence Possible pearlescenee, but very slight if present Definite pearlescence•these concentrates were white or silvery in appearance Very high pearlescence-•many of these concentrates are iridescent with it predominately bluish cast The products with a rating of 3 are of most interest and two of these are illustrated in Fig. la and b. All of the systems with a 3 rating were reeheeked. Some of those with a 2 rating were also cheeked but none with a 1 rating. Figure 1. .\queous pearlescent systems a POE (10) cetyl ether lauryl alcohol b. POE (20) stearyl ether myristyl alcohol

•582 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The solubility characteristics of the polyoxyethylene fatty ethers in water and their HLB values (4) are also listed in Table I. The HLB values indicate the relationship between the hydrophilic and lipophilic properties of the surfactants (5). The data show that only surfactants with a certain degree of water solubility or dispersibility give pearlescent products. Polyoxyethylene fatty ether surfactants that were insoluble in water or had HLB values below 12 did not give pearlescent systems. Myristyl and cetyl alcohols were the most consistent of the alcohols in producing pearlescent systems. In the previous study of these complexes it was also noted that myristyl and cetyl alcohols were generally the most effective in improving the properties of the foams (2). Polyoxyethylene Fatty •Ether/Fatty Acid Combinations--The optical properties of aqueous concentrates prepared with combinations of the 11 polyoxyethylene fatty ether surfactants with lauric, myristic, palmitic, and stearic acids were also determined. Forty-four combinations were evaluated, but only one was of any real interest, and that was the mixture of polyoxyethylene (4) lauryl ether and lauric acid. This combination gave the most iridescent concentrates that were obtained. Examples of these are illustrated in Fig. 2 (see p. 584). The colors of the samples varied, depending upon such factors as the temperature, the extent of shaking, the type of light used for illumination, etc. One sample showed no iridescence immediately after preparation and consisted of white, fluffy clouds of the components suspended in the aqueous medium. When the sample was shaken, it immediately became brilliantly irides- cent. Unfortunately, the iridescence of this system is destroyed by the addition of propellant. Polyoxyethylene Fatty t•ther/Cetyl Alcohol/Palmitic Acid Combina- tions-The optical properties of mixtures of the polyoxyethylene fatty ethers with a combination of cetyl alcohol and palmitic acid were also investigated. Only the four polyoxyethylene fatty ethers with the high- est HLB values gave peadescent systems and all of these had a pearles- cent rating of 3. The polyoxyethylene fatty ethers were POE (23) lauryl ether, POE (20) cetyl ether, POE (20) stearyl ether, and POE (20) oleyl ether. The relationship between the water solubility of the polyoxyethylene fatty ethers and the pearlescence of the resulting con- centrates was quite apparent in this series. Polyoxyethylene Fatty Ether Combinations--The only combination of two polyoxyethylene fatty ethers that gave a pearlescent concentrate