COMPRESSED GASES AS PROPELLANTS FOR COSMETIC PRODUCTS 229 the product residues when the dispenser is nearly empty can be determined experimentally and is also related to the product viscosity. The initial pressure is usually dictated by the strength of the dispenser, and by employ- ing Boyle's Law it is possible to calculate the ullage necessary. It may, however, be found that the ullage is of such magnitude that it could be preferable, particularly if the product viscosity cannot be adjusted, to incur somewhat larger product residues in order to decrease the ullage to reasonable proportions. So far as one can judge, it would appear to be United States practice to pack toothpastes into 6 oz. dispensers with an ullage of 30-33« per cent and an initial pressure, at 70 ø F, of 95-105 p.s.i.g. The pressure characteristics of nitrogen and similar gases are such that for every 10 ø F increase in temperature the pressure increases by only 2 p.s.i.g. It is therefore possible to utilize the conventional low-pressure dispensers, though at the moment only seamless containers* are employed. By reference to the gas laws it will be realized that only a very small quantity of gas is present in a 6 oz., or even a 20 oz., dispenser. Together with the low cost of propellants, such as nitrogen, this is obviously of great economic importance, but at the same time it creates almost the greatest danger. Accidental discharge of the propellant, or loss of the propellant due to mechanical faults, will lead to partial and possibly total inactivation of the pack. In order to avoid the former, the viscosity of the product must be right and it is necessary to ensure that the directions for use are followed by the consumer. Choice of the right container and valve together with proper quality control in the course of the filling operation can usually overcome loss of the propellant due to mechanical faults. Nitrogen and argon do not induce increased corrosion in the presence of water, as is the case with certain chlorofluorohydrocarbons. The chilling effect on the skin is also avoided. Oxygen, on the other hand, is almost certain to be present even if only in traces, and may well have an adverse effect on the perfume or flavour. Care must also be taken to ensure that the product viscosity does not alter with time and that there is no significant increase in the solubility of the propellant in the product on prolonged storage, which could affect the emission characteristics. These are but a few of the factors which will indicate that all pressurized packs, whatever the nature of the propellant, need careful pre-marketing storage tests. [Received: 14th October 111581 *Seamless Container •: One-piece body formed by pressing or drawing.

230 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS REFERENCES • •lerosol •Ige. 2 (October 1957). 102a. 2 Root. M. J. Package t•ngineering. 3 (May 1958). 28. 2 U.S. Pat.: 31,894. 4 U.S. Pat.: 3,723,200. 5 Glass Packer. 3õ (July 1956). 43. 6 Drug • Cosmetic Ind. 79 (1956). 101 7 -packaging -parade. 2!t (July 1956). 59. 6 Shepherd, H.R. Food _Processing. 19 (February 1958). 30. 9 Briston, J. H. _Packaging. •t0 (June 1958). 80. •o Modern _Packaging. 28 (August 1955). 91. n _Packaging _Parade. 2!t (May 1956). 25. t2 Chem. Ind. $•1 (1949). 205. xa Herzka, A. J. Soc. Cosmetic Chemists. 7 (1956). 350, 352. • Aerosol News (Fall 1957) 1. (E.I. du Pont de Nemours & Co. Inc., Wilmington, Del. U.S.A.) t5 G_P-- 1. (Ohio Chemical & Surgical Equipment Co., Madison, Wisc., U.S.A.) • •lerosol •Ige. 3 (July 1958). 18. •? Herzka, A., and Pickthall, J. _Pressurized _Packaging (•1erosols) (1958). 344. (Butter- worths Scientific Publications, London.) DISCUSSION MR. R. M. MUMFORD: What is the pressure in the hair lacquer pack demonstrated, (a) initially, (b) finally, and (c) is the final performance satis- factory ? THE LECTURER: (a) 90 p.s.i.g., (b) approx. 10 p.s.i.g., just prior to the final spray. A Precision break-up spray valve is used and the final spray appears satisfactory to me. DR. W. MITCHELL: Would it be possible to use a silicone resin as an internal lubricant ? THE LECTURER: An internal coating of this type would increase the cost of the container. There are reputed to be some U.S. Patents on such internal coatings •. It is, however, far easier and more satisfactory to tackle this problem via the viscosity of the product. MR. A. G. MCGEE: I have noticed from your demonstration that the spray cone from the break-up spray valve is far wider than from a conven- tional valve. Is this an inherent feature of this type of valve ? THE LECTURER: The spray cone varies with the formulation. But for any given formulation the spray cone from the break-up spray actuator will be wider than from an ordinary actuator' Some of the pictures shown to-night by Mr. Dixon indicated this very clearly. DR. H. W. HIBBOTT: Would it be possible to arrange for the dip tube to move with the liquid ? THE LECTURER: There is a U.S. Patent on such a valve modification, but it is only of use when the viscosity of the liquid is very low.