496 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (21} Shalita, A., Genesis of free fatty acids. I. invest. Demi. 62, 332-333 (1974). {22) Swmlbeck, G., A new principle for the treatment of ache. Acta derm.-venereol. (Stockh.) 32, 406-410 11972). {23} Voss, ]. G., A microbial etiology of acne. Cutis 17, 487-496 (1976}. [24) Wolf, W., Ober die Beeinflussung der anaeroben Baktenenfk)ra im Talgdrtisen- aus-t45hrungsgang dutch eine athyllactat- und iithanolhaltlge Filmmaske trod eine anti- mikrobielle Tensidl•')sung. Inauguraldissertation Heidelberg 1978. Wir danken der Deutschen Forschungsgemeinschaft ftir die Untersttitzung der Unter- suchungen. Wir danken Herin Dr. K. T. Holland [Department of Microbiology, University of Leeds} und Herin Dr. G. Scheurlen (Institut ftir Medizinische Dokumentation, Statistik trod Daten- verarbeitung der Universitiit Heidelberg} ftir ihre Untersttitzung bei der Durch 'kthrung der Untersuchungen.

J. Soc. Cosmet. Chem., 29, 497-521 (August 1978) Cosmetic properties and structure of fine-particle synthetic precipitated silicas S. K. WASON J. M. Huber Corporation, Chemicals Division, P.O. Box 310,Havre de Grace, MD 21078. Received September 3 O, 1977. Presented at Annual Scientific Meeting, Society of Cosmetic Chemists, December 1977, New York, New York. Synopsis Submicron-fine particle, synthetic silicas are of three types: fumed silicas, silica gels and precipitated silicas. Recent research has led to the synthesis of a wide variety of new controlled-structure, functional-precipitated silicas which exhibit unique cosmetic and dentifrice properties. The end-use api•lications of the precipitated silicas can be controlled by controlling their structure. It is now possible to make predictions regarding the thickening, viscosity building, humectant demand index, dentifrice abrasive and polishing characteristics of the new class of synthetic, precipitated products. The methods of preparation, the chemistry, the structure and the new cosmetic applications of the precipitated products are discussed. I. INTRODUCTION Fine-particle, synthetic silicas are amorphous, submicron size, white powders. In the literature, these products have often been referred to interchangeably as silicas, hydrated silicas, silicon dioxide, silicic acid, fillers, silica pigments, xerogels, aerogels, amorphous silicas, etc. The discussions which will be presented here will hopefully clarify and distinguish between the various types of silicas. Silicas can be categorized into two major classes: natural silicas and synthetic silicas. Since the natural silicas are mined from the ground and are quite different in structure, properties and functions than the synthetic silicas, we have excluded these products from our discussion here. Synthetic silicas are of three types: fumed silicas, silica gels and precipitated silicas-- and are prepared either by a vapor phase process or by a liquid phase process. Products which are synthesized by the vapor process are called fumed silicas. The products which are derived from the liquid process or wet process are further categorized as silica gels or precipitated silicas. In the CTFA (Cosmetic, Toiletry and Fragrance Association) cosmetic ingredient dictionary (1) the adopted name for the precipitated silicas and silica gels is hydrated silica the fumed silicas are referred to as silicas. For the present discussion we will first review the key properties of the three types of silicas. Then we will discuss the results of our recent research investigation in which we 497