FORMULATING AEROSOLS TO OBTAIN SPRAY PATTERNS 289 (11) Ostwald, Wo., Kolloid-Z., 6, 103 (1910). (12) Cheesman, D. F., and King, A., Trans. Faraday Soc., 34, 594 (1938). (13) Dixon, H. H., and Bennet-Clark, T. A., Nature, 124, 650 (1939) Proc. Roy. Dublin Soc., 19, 422 (1930) Ibid., 20, 211 (1932). (14) Chem. Specialties Mfrs. ,4ssoc. Proc., 43rd /lnn. Meeting, Dec., 1956. (15) Boe, C. F., U.S. Patent No. 2,524,590. (16) Kirk, R. E., and Othmer, O. F., editors "Encyclopedia of Chemical Technology," Vol. 5, New York, Interscience Encyclopedia, Inc. (1950). (17) Propellents referred to in this paper are all the trade name Freons made by E. I. du Pont de Nemours and Co., Inc. HOW TO FORMULATE AEROSOLS TO OBTAIN THE DESIRED SPRAY PATTERN By MARIA V. WIENER* Presented September lB, 1957, New York City THE FORMATION of proper spray patterns often constitutes a prob- lem to aerosol chemists and producers. It is of the utmost importance to formulate each aerosol product with a spray pattern best suited for the intended application. Room deodorants, for example, require very fine atomization in order to keep the active ingredients air-borne for a long time for better effectiveness. On the other hand, the efficiency of colognes does not depend upon an extremely fine particle size as required for room deodorants. Moreover, the colognes require a directed spray, for the purpose of deposition only at the desired spots, and without formation of too small droplets that would not strike the target surface but would be dispersed in the air, and therefore, wasted. THE DRoP SIZE DXSTRIBUT•ON OF SPRAY The spray pattern of an aerosol is best described by the drop size distribu- tion. There are two ways of presentation of drop size distribution in a spray. The one recommended by the Chemical Specialties Manufacturers Association uses the cumulative weight per cent method which records the weight per cent of the spray, with a particle size smaller than or equal to a given diameter (in microns). The mass median diameter is the drop size which divides the spray, so that 50 per cent of it by weight falls below the median diameter and the balance consists of equal or larger particles. Particle size distribution in an aerosol spray often follows the normal logarithmic distribution curve if plotted on a probability graph paper it gives an almost straight line. In Fig. 1, which represents the drop size * Fluid Chemical Co., Inc., Newark, N.J.

FORMULATING AEROSOLS TO OBTAIN SPRAY PATTERNS 289 (11) Ostwald, Wo., Kolloid-Z., 6, 103 (1910). (12) Cheesman, D. F., and King, A., Trans. Faraday Soc., 34, 594 (1938). (13) Dixon, H. H., and Bennet-Clark, T. A., Nature, 124, 650 (1939) Proc. Roy. Dublin Soc., 19, 422 (1930) Ibid., 20, 211 (1932). (14) Chem. Specialties Mfrs. ,4ssoc. Proc., 43rd /lnn. Meeting, Dec., 1956. (15) Boe, C. F., U.S. Patent No. 2,524,590. (16) Kirk, R. E., and Othmer, O. F., editors "Encyclopedia of Chemical Technology," Vol. 5, New York, Interscience Encyclopedia, Inc. (1950). (17) Propellents referred to in this paper are all the trade name Freons made by E. I. du Pont de Nemours and Co., Inc. HOW TO FORMULATE AEROSOLS TO OBTAIN THE DESIRED SPRAY PATTERN By MARIA V. WIENER* Presented September lB, 1957, New York City THE FORMATION of proper spray patterns often constitutes a prob- lem to aerosol chemists and producers. It is of the utmost importance to formulate each aerosol product with a spray pattern best suited for the intended application. Room deodorants, for example, require very fine atomization in order to keep the active ingredients air-borne for a long time for better effectiveness. On the other hand, the efficiency of colognes does not depend upon an extremely fine particle size as required for room deodorants. Moreover, the colognes require a directed spray, for the purpose of deposition only at the desired spots, and without formation of too small droplets that would not strike the target surface but would be dispersed in the air, and therefore, wasted. THE DRoP SIZE DXSTRIBUT•ON OF SPRAY The spray pattern of an aerosol is best described by the drop size distribu- tion. There are two ways of presentation of drop size distribution in a spray. The one recommended by the Chemical Specialties Manufacturers Association uses the cumulative weight per cent method which records the weight per cent of the spray, with a particle size smaller than or equal to a given diameter (in microns). The mass median diameter is the drop size which divides the spray, so that 50 per cent of it by weight falls below the median diameter and the balance consists of equal or larger particles. Particle size distribution in an aerosol spray often follows the normal logarithmic distribution curve if plotted on a probability graph paper it gives an almost straight line. In Fig. 1, which represents the drop size * Fluid Chemical Co., Inc., Newark, N.J.