LIQUEFIED HALOCARBON AEROSOL SYSTEMS 559 propellants may be used, provided that the surfactants are soluble in one and less soluble in the other (titrating) propellant. Description of ntpparatus: The plexiglass safety tube fbr a three-ounce Fischer and Porter aerosol compatibility tube was modified to convert it into a constant temperature jacket for the apparatus (Fig. 6). The jacket was fitted with inlet and outlet tubes to permit the circulation of water which maintained a constant temperature in the apparatus. The circu- lating water was maintained at 25øC and was pumped into the jacket at in- let tube (K) and back into the constant temperature bath from the outlet tube (C). To minimize subjective errors in arriving at a sharp and reproducible endpoint, a photoelectric cell and a light beam were positioned on both sides of the tube so as to permit the fixed beam of light to pass through the contents of the tube and then register on the photoelectric ceil at the oppo- site side. The light beam was generated by a small but powerful spotlight (G) mounted on an adjustable base. The Plexiglass jacket was completely covered with black Velcro* fastener tape (E) to prevent any incident or re- flected light from entering the tube and thus interfering with the reading of the light beam intensity. Velcro tape was selected as the lightproof cover since it could be removed and reapplied to the apparatus many times with- out losing its ability to adhere. A strip of the female portion of the tape was cut away to permit reading of the millimeter reference scale on the glass tube. During each determination this was covered with a corresponding male strip. Small holes were also cut into the Velcro tape to permit the beam of light to enter the tube and to emerge at a point on the opposite wall where it registered on the photoelectric cell. A view of the contents at right angles to the beam of light was provided by another small opening in the tape (F). The photoelectric cell utilized in this apparatus was a Model S Brockway Exposure Meter** (J). The light scale on the photometer permitted reading of the endpoint directly in each cloud point determination. The intensity of the light beam passing through the clear solution of surfactant at the start of each determination was adjusted to produce a reading of 250 footcandles on the photometer scale. The endpoint was read when a cloud was produced which scattered the beam of light sufficiently to register only $ footcandles on the scale. A cloud point determination was carried out by first accurately weighing 4.0 g. of the surface-active agent in the glass tube (D). A magnetic ball stirrer (H) was placed in the tube. The tube was sealed with a stainless steel adaptor to which was fitted a toggle valve (A). The adaptor was * Velcro Corporation, 681 Fifth Avenue, New York, N.Y. 10022. ** Brockway Camera Corp., New York, N.Y. 10038.

560 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS secured in place by means of the nylon packing and aluminum packing nut (B) normally used to hold a standard 1 in. aerosol can valve in the mouth of the compatibility tube. As an additional measure against leakage of pro- pellants, the adaptor was constructed with an "O" ring and a rubber gasket. This assembly was then placed on a magnetic stir plate (I) and connected by means of a flexible pressure hose attached to the valve (A) to a Foresman Liquid Gas Manipulator* which in turn was connected to a propellant supply tank. The propellant mixture under investigation was then pres- sure-filled into the apparatus. A quantity of propellant just short of the calculated amount was introduced into the tube. This was permitted to reach a temperature of 25øC, and then the volume was carefully adjusted by adding more propellant. The millimeter reference scale on the glass compatibility tube had been calibrated so as to enable the conversion of propellant volume to weight. The final adjustment was made in the vol- ume of the contents to produce a total of 20 g. of solution. Thus, every determination was carried out on a 20% (w/w) solution of a surfactant in a propellant mixture. With the light shield (E), spot light (G) and photometer (J) in position, the valve (A) was then regulated to admit Propellant 114 into the tube. When the vapor pressure of the propellant mixtures in the tube was higher than the vapor pressure of Propellant 114, the Foresman apparatus was used to provide a positive pressure to Propellant 114, and this permitted the addition of the propellant in controlled quantities. As Propellant 114 was slowly added to the surfactant solution in the tube, the rotation of the magnetic stirrer was adjusted to provide thorough mixing and to maintain the precipitate which ultimately formed in a state of moderate agitation. Titration with Propellant 114 was continued until the first appearance of a precipitate of the surfactant. Simultaneously, the indicating needle in the photometer registered a decrease in the light intensity. At this point the addition of Propellant 114 was discontinued, and in most instances the initial precipitate slowly redissolved while the photometer reading again approached 250 footcandles. The contents of the tube were permitted to reach 25øC, and then Propellant 114 was added slowly until the photometer reading was decreased to 5. A reading was made again after a short interval to insure temperature equilibration, and akiustments were made when necessary. A constant photometer value of $ was construed to indicate that none of the precipitate had redissolved and that the endpoint had been reached. The male Velcro strip was then removed to permit a reading of the final volume of the con- tents of the tube on the reference scale. The difference between the orig- inal and final volumes was used to calculate the weight of the Propellant 114 which had been required to produce the cloud point. * Robert A. Foresman, Jr., 1690 Margaret St., Philadelphia 24, Pa.