412 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS aerosol, the product being in one container and the propellant in a separate container ? THE LECTURER: I have not handled these personally. There are some perfume dispensers of this type in France. These have very complicated valves which increase the cost of the pack considerably. An alternative is the "Jet Pack", which has been licensed to one of the contract fillers in this country. A plastic handle incorporates a nozzle and a container of propellant 12 is utilized. A refillable product container is fitted, and oa operation the propellant passes towards the nozzle, and simultaneously draws up product from the reservoir in fact similar to the old-fashioned perfume atomizer. This type of pack is used mainly for paints. The U.S. Nebu-Halent pack for asthma sufferers is very similar in action. MR. W. A. WOODWARD i In pressurized packs of toilet powders, the particle size must be very important. Could you give us details of the range required for successful formulation ? THE LECTURER: Approximately 325 mesh. It all depends on the valve, and the amount of powder in the container. 8 per cent is the maximum with the majority of valves. I would also refer you to the work of Geary and West [Aerosol Age 6 25 (August 1961)_]. LETTER TO THE EDITOR Sir,--I refer to J. S. Jellinek's paper "Evaporation and the Odor Quality of Perfumes", in page 168 of the April 1961 issue of the Journal. I would like to comment that all these experiments show is that the rate of evaporation is influenced by the composition of the bulk. They do not indicate any reason for this, a/though conjecture is permissible, but fixation is not necessarily a result of molecular association as is advanced in this article. A substance completely inert to one of the smells covering say, -• of the surface of the perfume would decrease the odour concentration or balance of odour to approximately • due to the reduction of the uncovered surface under the conditions of the described experiment and thereby act as a "fixative". The relative factors in fixation are the extent of the surface available to the bulk molecules for their evaporation, the energy of their evaporation and the molecular reflexion properties of the surface, although this latter will not apply to the experiments described. [J. Soc. Cosmetic Chemists 7 69 (1956)5. Yours faithfully, Chesebrough-Pond's Ltd., A.W. MIDDLETON. Victoria Road, London, N.W. 10.

BOOK REVIEWS 413 BOOK REVIEWS INVESTIGATION OF RATES AND MECHANISMS OF REACTIONS. Second Edition. Editors: S. L. Friess, E. S. Lewis and A. Weissberger. (Series: Technique of Organic Chemistry, VIII, Part I). Pp. xii + 702 + Ill. (1961). Ltd., oeondon, 177s. There has been considerable revision of this book in the second edition and new chapters have been added on "Time measurement and recording of kinetic data", "Interpretation of rate data", "Use of computers", "Kinetic isotope effects" and "Hetergeneous reactions and catalysis". Other chapters include information on homogeneous gas phase reaction, homogeneous solutions, reactions and catalysis. Chapter II on the general theory of rate processes and a comparison of the collision and transition state theories is particularly clearly and concisely written. Much practical advice is given throughout the book and many warnings are issued concerning the danger of jumping to conclusions in kinetic work without sufficient evidence or the elimination of all other possible reaction paths. The formulation chemist would be interested in chemical kinetics from the point of view of deterioration and accelerated shelf life testing-the value of which is frequently horley debated. The systems usually under examination are much more complex than the simple ones studied in this book the simplest being dye fading and emulsion separation neither of which is discussed here. I feel that undoubtedly this book would be of great value to the kinetic chemist since it is very well documented (1,400 references) but it would be a luxury rather than a necessity for the cosmetic chemist. N.J. VAN ABBOT. TELOMERIZATION AND NEW SYNTHETIC MATERIALS. R. Kh. Freidlina and Sh. A. Karapetyan. Translation edited by B. P. Mullins. Pp. x + 102. (1961) Pergamon Press, Ltd., London. 25s. This book is a translation from a Russian edition published in 1959 and written by authors who have contributed to the considerable Russian research in this field. The Telomerization Reaction will already be well-known to many, but it may be explained that basically it consists of a reaction between a saturated compound and a polymerisable materiM, e.g. carbon tetrachloride and ethylene. The product from such a reaction is a mixture of "telomers", which are in effect low molecular weight vinyl polymers-in this particular case tetrachloroalkanes. CCI4-½n(CH2=CH2) --• CI(CH2--CH•)nCCIa The process is dependent upon the liberation of a free radical