JOURNAL OF THE SOCIETY absorption bases. Polyvalent salts (magnesium sulphate, for instance) actually tend to improve the emul- sion made from wool wax absorption bases. In cases where the wool wax possesses a fairly high acid value, there may be a danger of phase in- version when alkali is added, owing to the fortnation of an interfacial complex between the resulting soap and the woo] Wax alcohols. One of the most serious factors affecting the stability of cosmetic creams made from absorption bases is the nature of the added perfume. Many per- fumery ingredients, notably the ter- pene alcohols and in particular ter- pineol, have a strongly adverse affect upon water-in-oil emulsions stabil- ised by wool wax. An emulsion pro- duced by adding 50 parts of water to 50 parts of a really efficient absorption base will tolerate up to 2• parts of terpineol. It is surpris-. ing how little of this alcohol can be incorporated in creams made from most of the bases now offered to the industry. In fact, the technique of assessing the amount of terpineol which a cream of this type will toler- ate may be used as a yard-stick whereby the stability of the emulsion can be measured. The answer lies in the use of the correct type of jelly, but very great care must be exercised in choosing a perfume for the cream the chemist intends plac- ing on the market. It is misleading to read that soaps of polyvalent metals are water in- soluble but oil-soluble. Metallic soaps such as calcium and mag- nesium, stearates are practically in- 152 OF COSInETIC CHEMISTS soluble in mineral oil when in the anhydrous state. Aluminium stear- ate, although soluble in mineral oil at elevated temperatures, is not a trne soap but rather an absorption compound. Traces of water no doubt aid the dispersion of metallic soaps, but it is really necessary to prepare w/o emulsions employing polyvalent metal stearates by either an inversion process or by the use of a water-soluble polyvalent ion. An example of this is the common combination of mineral oil, beeswax, and lime water, which produces emulsions far more efficiently than is possible directly from a calcium •oap. Certain non-ionic bodies are most efficient w/o emulsifiers, and special mention should be made of the pro- prietary Sorbitan Sesquioleate. The use of oil-soluble non-ionic agents in conjunction with the water-soluble type to produce w/o emulsions i.q of interest. A study of the oleates of the poly glycols is strongly recommended. These esters are available in several types, graded according to the mole- cular weight of the poly glycol. The reference number given to these oleates usually reveals their nature. Thus, a figure of 400 would suggest that the ester has been made from a poly glycol with an average molecu- lar weight of approximately 400. (The condensation of 9 molecules of ethylene glycol would give a product possessing a molecular weight of 414, while 4 molecules of diethylene gly- col would condense to yield a pro- duct with a molecular weight of

]E3 IULS•[ON• ANB Tile COSMETIC CltEMI$i 370.) Above "300" the poly glycol oleates tend to become too water- soluble to be of interest as w/o emulsifiers, but diethylene glycyl mono oleate is a very good w/o emulisfier. The grade described as "200" which approximates to tetra ethylene glycyl oleate is a truly amazing substance. When five parts of this material are dissolved in 95 parts of petroleum jelly, it is possible to stir in 100 parts of water with ease, to produce an attractive and stable w/o cream. It is of grea• interest that the grade of petroleum jelly used does not affect the subse- quent emulsion in the same way as it does when used in conjunction with wool wax. If petroleum jelly is re- placed by mineral oil, then the addition of 100 parts of water results in a thin stable o/w emulsion. Quite apart from the interest that this par- ticular emulsifier arouses, this experi- ment demonstrates the importance of the petroleum products used in cos- metical preparations. SUMMARY Many chemists will undoubtedly call to mind examples of emulsions which are not completely explained by the theories so far outlined. Nevertheless, it can be said that with these theories before them it is pos- sible to approach the formulation of new emulsified products with a better understanding of the funda- mental requirements of the emulsi- fier. The theories may also assist the chemist to overcome certain of his existing difficulties. These theories offer a reasonable explana- tion of the mode of action of certain established emulsifiers and open the way to further research. BATH ESSENCES AND PREPARATIONS OF THE "MISCIBLE OIL" TYPE The preparations to be discussed under this heading are those in which mixtures of oil and water are presented in clear dispersed form. They are sold in the form of attrac- tive transparent liquids which, when poured into water, disperse in an emulsified state with the liberation of fragrant odours. It is possible to produce similar preparations which remain clear when diluted with water, but the cloudy dispersions are more popular in the bath and for sprays and disinfectants, and fit more neatly into the subject of this paper. The "miscible oil" will consist of a four component system: water, oil, emulsifying agent and an auxili- ary solvent. Water is a necessary and desirable constituent of the system and for reasons of economy should be present in as high a con- centration as safety limits permit. It is generally essential to use dis- tilled water. The oil will consist of a mixture of essential oils, synthetic and natural chemicals blended into the form of a compound perfume, and the amount present in the pre- paration will be determined by the consideration of 'strength of odour and price. The proportions of emul- sifier and "auxiliary solvent" should be kept as low as is consist- ent with the clear dispersal of the 153