370 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS and the temperature then regulated to around 45-55øC. The aqueous ingredients are placed in solution and heated to around $' o •-60 C., or in any event, 5 ø more than the oil phase. The aqueous solution is then slowly stirred into the oil phase. To avoid phase inversion, each succeeding portion is added only after the previous portion has been emulsified. The resulting emulsion is stirred with relatively slow agitation until completely cooled. It is widespread custom to homogenize water-in-oil emul- sions by running them through a colloid mill or similar device for re- ducing particle size. This proce- dure is also used, in some instances, for oil-in-water emulsions, but it is not the general practice. It is seen that emulsions of this category are not too difficult to formulate and that some general rules may be laid down as a guide. The following, although admitting of exceptions, have served the writer for a number of years: 1. The volume (or weight) of the disperse phase should be greater than that of the dis- persed phase. 2. All of the ingredients of either phase must be miscible with the other ingredients of that phase. 3. If the stability of an emul- sion is dependent on homo- genizing or similar specialized mechanical handling, it should be reformulated because it is basically unstable. 4. When other factors permit, it is preferable to formulate an oil-in-water rather than a water-in-oil emulsion. The vehicle-type preparations do not admit of the generalizations re- garding formulation or manufactur- ing procedure noted for the non- vehicle types, as the emulsifiers used are more complex .and highly spe- cialized. In addition, the additive which gives the desired effect is a stranger to the emulsion scheme and the question of compatibility there- fore arises. The task of incorporat- ing the additive in the emulsion is the essence of successful formulation in vehicle-type preparations of this category. We will take the astrin- gent deodorant cream as an example of this type of preparation, and of the difficulties to be encountered. The function of an astringent de- odorant cream is to act as a vehicle for the astringent material--usually an aluminum salt. The aluminum salt is said to react with the skin protein and form an aluminum al- buminate, the resulting coagulant closing the openings on the skin surface and acting as a bar to epi- dermal excretions at the site of ap- plication. The vanishing cream type of deodorant has gained in popularity and seems to be the most acceptable from the consumer's point of view. Even at this time, cosmetic for- mulators new to the problem ask if it is possible to simply add the re- quired amount of an aluminum salt to a standard vanishing cream. Of course, when the ingredients of this type of cream are examined we know

PRACTICAL ASPECTS OF that this is not possible. A concen- trated solution of highly acidic salt, such as aluminum sulfate, will break the conventional type of vanishing cream formulated with potassium, or sodium stearates or other sapo- naceous emulsifiers. Nor will the various glycol or glycerol esters of stearic or other fatty acid do the trick, inasmuch as their emulsifying properties are dependent upon the presence of soap. However, acid stabilized emulsifiers have been de- veloped, some specifically for this particular application. These may be broadly classified into three main groupings: the sulfated, the amide, and the non-ionic types. In some cases, these emulsifiers are used in conjunction with glycerol or glycol stearates, etc., or even in combina- tion with each other. Representa- tive astringent cream formulas are shown in Fig. 2. With these highly Figure 2.--Typical Astringent Deodorant Creams 1 2 3 Emulsifier 18' 5 •- 11 { Stearic Acid' 15 Cetyl Alcohol i15 3 4' Petrolatum 1 3 Glycol Stearate .. •' Mineral Oil •15 .... Carbamide 5 Humectant 3 '3' ' ' Water 53 52 5•' Aluminum Salt 15 18 15 Titanium Oxide 1 1 1 * Sulfated. t Amide. $ Non-ionic. specialized emulsifiers it is possible to formulate stable creams contain- ing sufficient quantities of aluminum or other astringent salts to ade- quately inhibit the flow of perspira- tion. EMULSION FORMULATION 371 However, there are other aspects of the problem of deodorant cream formulation. All of the commonly used astringent salts, to a greater or lesser extent, have a destructive ef- fect upon fabric, particularly cot- ton so that when the user's gar- ment is laundered it is often found that the fabric is completely de- stroyed near the site of application. It is, therefore, desirable to have a deodorant cream formula contain an inhibitor, which will lessen the tendency of the astringent material to attack fabric. Carbamide, or urea as it is commonly known, which has lately been the subject of some prolonged patent litigation, is widely used as an inhibitor. There are other materials which exert a simi- lar effect. Some of the more complex amides, for instance, do a good job in very much lower percentages than car- bamide. For this reason, it has been suggested that the amide-type emulsifiers are particularly suitable for use in deodorant creams. In some instances, they are used in conjunction with emulsifiers be- longing to the other two types as emulsion stabilizers as well as in- hibitors. However, it should be noted that while these materials tend to inhibit the fabric-destroying properties of the aluminum salts, there is much evidence to indicate that they also inhibit the astrin- gent properties almost proportion- ately. It is therefore necessary for the formulator to strike a balance between the inhibiting properties in relation to fabric destruction and