Elements of Fractional Distillation By CLARK SHOVE ROBINSON AND EDWIN RICHARD GLLLILAND. PREFACE TO THE FOURTH EDITION: This book and the early revisions were the result of the efforts of Professor Robinson, and he took an active part in guiding the revision of the previous edition. His death made it necessary to prepare this edition without his helpful guidance and counsel. The present revision differs extensively from the previous edition. The material has been modified to bring it more closely into line with the graduate instruction in distillation at Massachusetts Institute of Technology. Much greater emphasis has been placed on the measurement, prediction, and use of vapor-liquid equilibria because it is believed that this is one of the most serious limitations in design calculations. Greater emphasis has also been placed upon the use of enthalpy balances, and the treatment of batch distillation has been considerably expanded. Unfortunately, the design calculations for this type of operation are still in an unsatisfactory status. Azeotropic and extractive distillation are considered as an extension of conventional multicomponent problems. The sections on column design and column performance have been completely rewritten and increased in scope. In all cases quantitative examples have been given because it has been found that this greatly aids the student in understanding descriptive material. During the last 15 years a large number of design methods have been proposed for multicomponent mixtures, some of which are reviewed in Chapter 12. Most of these do not appear to offer any great advantage over the conventional Sorel method, and it is believed that the law of diminishing returns has been applying in this field for some time. It is hoped that the present edition will stimulate some of these investigators to transfer their efforts to more critical problems, such as vapor-liquid equilibria, batch distillation, transient conditions within the distillation system, and column performance.