Laboratory Preparation of Cold Cream to Show saponification and Emulsification GEORGE W. HUNTER Hampton Institute, Hampton, Virginia
wax and the alkali, sodium hydroxide, forms a soap, sodium cerotate. Hauser states that gasoline and water form a stable emulsion with soap as the emul~ifier.~ It is felt, therefore, that mineral oil and water will form a stable emulsion with sodium cerotate as the emulsifying agent. To make a simple cold cream, place 16 g. of white beeswax and 50 cc. of mineral oil into a 250-cc. beaker. Place this beaker in a water bath and heat until the wax melts. Obtain the temperature of the melted mixture. Whie the wax is melting, place 1 g. of borax and 33 cc. of water into a 100-cc, beaker. Heat over a wire gauze until the temperature of this solution is withim two to five degrees centigrade of that of the oily solution. Slowly pour the borax solution into the melted oils, stirring constantly. The mixture will turn milky due to the saponification of cerotic acid in the beeswax, forming first a soap and then a "water-in-oil" emulsion when cool. After the cold cream is made and while it is still hot, pour 5 cc. into each of four test tubes and immerse in cold water to allow them to set. Measure into four test tubes 5 cc. of the following: water, melted beeswax, mineral oil, and 1 per cent borax solution, respectively, and heat to 70°C. in a water bath. Pour the contents on top of the respective test tubes of cold cream and remelt in the water bath the four test tubes of cold cream containing d'ierent ingredients. On removal from the bath and recooling in iced water, it is found that both mineral oil and beeswax dilute the cold cream emulsion but water and borax are immiscible in the tubes containing cold cream. It is felt, therefore, that the simple cold cream made is a "water-in-oil" emulsion. This experiment may be repeated with the remaining cold cream left in the 250-cc. beaker. , The preparation of the simple cold cream embodies an explanation of the saponification of fatty acid with an alkali and the emulsilication of the oil and water to form a stable emulsion. Thii emulsion was proved to be one of the water-in-oil type as addition of further ' A D A M ~AND JOHNSON, "Elementary Laboratory Experi- water caused the latter to separate, whereas the addiments in Organic Chemistry," The Macmillan Company, New tion of oil increased the oily layer of the "water-in-oil" York, 1940. p. 161: FUSON.CONNOR, PRICE.AND SNYDER. "Brief Course in Organic Chemistry," John Wiley and Sons, emulsion. Oil can be added to a perfectly balanced Inc., New York, 1941, p. 213. "water-in-oil" emulsion but water cannot. WALL. "A fertile field for chemical research," J. CHEM. Eouc., 17, 79 (1940). HnusEn. "Colloids in your daily life." J. C ~ MEDUC., . 18,
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NUMBER of experiments have been tried in the laboratory for the preparation of soap with varying degrees of success.' Included in these experiments is the study of fats, waxes which contain fatty acids, and emulsifying power of soap. It has been found helpful for the large number of home economic students taking organic chemistry to make a simple cold cream and illustrate from this both saponification and emulsification. Accord'mg t o Wall,=too many amateurs are flooding the market with kitchen-made products which compete unfairly with those of legitimate manufacturers. This experiment is not one to compound a cosmetic formula but to serve as a basis for the scientific study of one small problem of this vast and valuable industry. A given volume of an inorganic or organic acid will require a definite volume of a base for its neutralizalion. If a fatty acid is used the process is called saponification and the product, a soap. A perfectly balanced "oil-inwater" emulsion cannot be diluted with additional oil. Adding oil to increase viscosity of such an emulsion will cause i t to separate. Similarly water cannot be added to a perfectly balanced "water-in-oil" emulsion. A simple cold cream may consist of four ingredients: white beeswax, mineral oil (light liquid petrolatum), water, and borax, which may be purchased a t any reliable chemical house. Beeswax consists chiefly of free cerotic acid and myricyl palmitate with small quantities of other higher fatty acids and alcohols, and about 10 per cent of hydrocarbo~s.~It may be bleached white by exposing the wax in the form of thin films to the action of moist air and sunlight. Mineral oil is a colorless, oily mixture of liquid hydrocarbons insoluble in water and obtained from petroleum. Borax in water solutions hydrolyzes to form sodium hydroxide and boric acid. Although there are secondary reactions, the reaction of cerotic acid from bees-
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Encyclopedia Britannica, Vol. 3. 14th ed., p. 316.
593, (1941).
