SYNTHETIC ESTER DISPERSING AGENTS 219 propylene gylcol monoisostearates. It can also be noted that little, ff any, dif- ference existed with regard to the usefulness of the isopropyl isostearate or propylene glycol monoisostearates as suspending agents for the other mate- rials studied. It is also interesting to note, that when comparing the settling rate of the solids used in this study in the presence of various dispersing agents, propyl- ene glycol dipleargonate was the least effective because the powders settled rapidly in the presence of th!s material. This material also showed the least solubility in the propellants. All of the samples showed a rather rapid rate of settling. In all cases, some settling occurred immediately with complete set- tling taking place in 4 to 5 min. Isopropyl myristate with aluminum chlorhy- droxide did not show settling for the first 15 sec, as is shown in Fig. 2. Very little difference was noted between the reading taken at the 5 min and 24- hour time intervals. The results shown should be considered to be relative and of help in comparing the usefulness of the various dispersing agents studied, but not as absolute values. Tables III and IV indicate the relative ease of redispersion of the solids using different esters. However, it is necessary to consider both rate of sedi- mentation and ease of redispersion when selecting a dispersing agent. It should be indicated that no anticaking agent, such at fumed silica was to be used in this part of the study. While the number of inversions required to effect redispersion would be different in the presence of an anticaking agent, it is believed that the relative order of usefulness of the esters would be the same. SVMM,•RY and Co•c•,vsIo•s A study was made to determine the effectiveness of various dispersing agents, when they were used as suspending agents in the presence of alumin- um chlorhydrate, starch, and talcum. The solubility of each of the dispersing agents in Propellants 11, 12, and 114 was also determined. A nonaerosol sys- tem, which was useful in screening various dispersing agents, was devised. Two methods of adding the dispersing agent to powder were studied and in- cluded addition of the dispersing agent directly to the propellant phase, as well as direct addition to the powder. Of all the dispersing a•ents studied. vropvlene glycol monoisostearate (and the 90 per cent monoester) were found to be the most effective suspending agents for aluminum chlorhydrate, starch, and talcum. Very little difference was noted among the other dispersing agents used in this study. (Received September 2, 1975) REFERENCES (1) A. Herska, Powder aerosols, I. Soc. Cosmet. Chem., 21, 553 (1970). (2) S.C. Elvin, Powder aerosols, Aerosol Age, 16, 26 (1971). (3) A.M. Rubino, Current Trends in aerosol antiperspirants, Amer. Per[urn. Cosmet., 86, 51 (1971).

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS (4) H. Mintzer, Powder aerosols, Aerosol Age, 13, 32 (1968). (5) J' J' Sciarra, "Pharmaceutical aerosols" in The Theory and Practice o[ Industrial Pharmacy," L. Lachman, H. A. Lleberman, and J. L. Kanig, Editors, 2nd Ed., Lea and Febiger, Philadelphia, Pa., 1976, •Pp. 278-80. ' ' (6) H. M. Lee and M. Coopersmith, Effect of cosmetic oils on aerosol antiperspirant formulations, Cosmetics and Perfumery, 88, 35 (1973).