This edition has again been written with the object of giving an account of the subject of laboratory distillat)ion including recent views and developments. The literature has been reviewed up to the year 1979. The author has adopted the course of dealing only with generally accepted facts ; there are still numerous problems in simple and countercurrent distillation which have not yet been completely clarified and in which there exist differences of opinion among various investigators. Distinct trends in development have nevertheless been mentioned, in order to give an incentive for further work. Owing to the large mass of material, a critical selection has been necessary. An attempt has been made to introduce the mathematical deductions and formulae required in laboratory work in a readily understandable form. Readers with a mathematical turn of mind and those interested in particular problems will find extensive references to the literature for further study.