Hydrogenation of the olefinic constituents of catalytically cracked aviation gasolines to the corresponding paraffins without hydrogenation of aromatic constituents to naphthenes results in a gasoline of improved stability and lean-mixture octane number after addition of lead, with no

signed. The charts and diagrams are good, and it is only occasionally with the color photographs, which are liberally used, that visual rather than illustrative values appear to have influenced the choice of a picture.The encyclopedia's machinery is serviceable. Indexing is adequate, crossreferencing is not irksome, topics usually are found where the reader expects them, and a 16-page bibliography points the way for those whose appetite has been whetted for more information.An encyclopedia must ultimately be judged on the basis of its usefulness, and the experience of using the Harper encyclopedia for several months has led this nonspecialist to expect to find what he needs. The Theory of Recycle Processes in Chemical Engineering. M. F. Nagiev. Translated from the Russian edition (Moscow, 1958) by R. Hardbottle. R. M. Nedderman, Ed. Pergamon, London; Macmillan, New York, 1964. xiv + 278 pp. Illus. $15.Fundamental concepts of the recycle processes used in chemical engineering are discussed in this book. In the petroleum and chemical industries it is common practice to separate the reaction products from the unconverted fresh feed by distillation, extraction, and crystallization when equilibrium limits the degree of conversion or prolonged exposure of the products in the reactor causes undesirable side reactions. These basic principles are developed in considerable detail in the text.Apparently the author is more mathematician than chemist because many of the minor but important interactions that occur in recycle processes are not mentioned, but when he deals with a single straightforward reaction, such as light hydrocarbon isomerization, where no by-products are formed, the mathematical derivations signed. The charts and diagrams are good, and it is only occasionally with the color photographs, which are liberally used, that visual rather than illustrative values appear to have influenced the choice of a picture.The encyclopedia's machinery is serviceable. Indexing is adequate, crossreferencing is not irksome, topics usually are found where the reader expects them, and a 16-page bibliography points the way for those whose appetite has been whetted for more information.An encyclopedia must ultimately be judged on the basis of its usefulness, and the experience of using the Harper encyclopedia for several months has led this nonspecialist to expect to find what he needs.

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