372 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS inhibiting factor as affecting the astringent properties of the alumi- num salts. Thus, we see the prin- ciple of balance or compromise being applied to cosmetic formula- tion. It is an important principle and is widely applied. Many cosmetic preparations are classic examples of the combination of opposing forces. The measure of the skill and "know how" of a cosmetic technician is often his abil- ity to achieve this balance. We can carry this concept a bit further in the same type of preparation. The higher the percentage of active in- gredient, i.e., astringent material, a deodorant cream contains, the greater its astringent properties, and the more effective will it be as a deodorant preparation. However, we have already noted that we can- not employ any desired percentage of aluminum salt: first, because of emulsion stability second, because of its effect upon fabrics. A third factor to be considered is the limit of solubility of the aluminum salts. Aluminum sulfate, for example,' is quite soluble in water but it is insoluble in most of the other com- monly used ingredients. Since it is necessary for these other ingredi- ents, emulsifiers, etc., to be present in order to form an emulsion, we have available only about 60-65 per cent of water, and in many in- stances the solubility of the alumi- num salts is decreased by the pres- ence of the o,ther ingredients. In any event, we end up with a prepa- ration containing a fairly concen- trated solution of aluminum salt: in many instances, a saturated solu- tion. Deodorant creams must last for some time, both on the shelves where they are sold and in the hands of the ultimate consumer. During its shelf life and while it is in use, there is bound to be a certain amount of evaporation of the water content from' the surface of the cream, resulting in crystallization of the aluminum or other astringent salt. This development makes the product objectionable in appearance and unsuitable for use. It has been demonstrated that it is necessary to have a sufficient amount of active ingredient (as- tringent) to exercise the primary function of a deodorant preparation, i.e., inhibit the flow of perspiration. The greater the amount of astrin- gent salt, the larger the percentage of emulsifier, stabilizer, or inhibitor required. But, the greater the amount required of the last three mentioned ingredients, the smaller the amount of water available as a solvent for the astringent salt. Hence, the need for balance or com- promise. So far, only the formulation dif- ficulties inherent in a typical vehicle emulsion, such as a deodorant cream, have been dealt with. Using the same example, the astringent deodorant cream, it may be of in- terest to note a few of the manufac- turing problems incurred. Employ- ing again, as we must, a general procedure, we note that the fats and oils are often heated together at around 75-80øC., and then stirred until an emulsion is formed. This

751. emulsion is stirred continuously :? until cooled, when it resembles a • rather stiff vanishing cream. The !?':.11 aluminum salts and other inorganic ili•:i': materials are then added very : slowly until dissolved or dispersed. : This procedure is critical and some- what tricky, inasmuch as the addL tion of the astringent salt results in a rise in temperature, which must be controlled by the introduction • of water in the cooling jacket of the "•':.mixing vessel or other suitable means. This, together with other factors, might result in an immedi- ate breaking of the emulsion and the spoilage of the particular batch. After the salts are added, the cream is ready for the introduction of per- fume, which is added rather slowly in order to insure complete mixing. Titanium oxide is usually included' in formulations of this type. For this, and other reasons, it is often considered advisable to mill the entire cream in order to insure dis• tribution of the inorganic material. Here again a note of caution is ad- vised the peculiar nature of the materials tends to dull the surface of the milling machinery, even after only one run, particularly when colloid mills are employed, EMULSION FORMULATION 373 where clearances are rather close. In view of the foregoing, it would seem that hardly any of the broad generalizations which were applied to .the preparation of emulsions of the non-vehicle type can be applied to those of the vehicle variety. Each product in this category has to be considered as an individual prob- lem. The trend, if anything, is for preparations of this sort to become more and more complex. Fortu- nately, there is an ever-growing num- ber of materials available to which the cosmetic technician may look as a means for solving his problems. These materials are not only in- creasing in number and variety they have become more uniform and standardized than they were only a few years ago. By becoming acquainted with the properties and limitations of the latest develop- ments in the field of synthetic emul- sifiers and other surface-active ma- terials, the cosmetic chemist will find that he has available a vast potential storehouse of highly spe- cialized tools to assist him in meet- ing the varied and intricate prob- lems presented in the equally highly specialized realm of cosmetic emul- sion technology.