PROPELLENT IN AEROSOL PRODUCTS 141 with high boiling compounds, such as alcohol, and still produce the desir- able spray pattern and particle size. It should be of interest to point out that the thermodynamic properties ofthe"Freon" compounds have been very thoroughly investigated. Quite comprehensive charts and tables of these properties have been published. For the development of aerosol products, it is more important to know the temperature-pressure relationships of solutions of these propellents than the pure compounds. These data have been published for all binary systems of interest to the aerosol industry (2). An example is the set of curves for "Freon-12"-"Freon-11" solutions shown in Fig. 3. In this S'T & TENpIrI•ATURIr- OEGRIrlr S •r HIrN T ( I Figure 3. chart a family of curves has been constructed relating pressure to tem- perature at 10 per cent intervals by weight of the "Freon" compounds. Thus it is possible to estimate the vapor pressure of any "Freon-12"- "Freon-11" solution with an accuracy of 1 psi. over quite a wide tempera- ture range.

142 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS LIQUID DENSITY Density is a further property of the fluorinated hydrocarbon propellents worthy of a few moments consideration. As one would expect, the liquid T•.SLE 4--LIqum DENSXTXES Propellent '' o Density, g./cc. --- 7O F. 130øF. "Freon-22" 1.209 1.063 "Freon-12" 1.323 1.193 "Freon-114" 1.470 1.360 "FreonAl" 1.485 1.404 densities are relatively high for organic compounds as indicated in Table 4. Densities are an important consideration in the laboratory development and commercial loading of aerosol formulations. As was the case with vapor pressures, it often is of more direct concern to know the densities of solutions of the "Freon" compounds. Curves describing the densities of "Freon-12"-"Freon-11" solutions and "Freon-12"-"Freon-114" solutions have been published (3). They are in a form similar to the vapor pressure curves. As an example, Fig. 4 shows the family of curves developed for the density of "Freon-12"-"Freon-114" solutions.