The assembly of the table of values for the heats of formation in the section on Thermochemistry in the International Critical Tables was the first attempt ever made to collate all the published data involving heats of reaction and to prepare therefrom a self-consistent table of ''best'' values for the heats of formation of the chemical substances. The present book is a complete revision and extension of that original work, which was sponsored by the late Edward W. Washburn as Editor-in-Chief of the International Critical Tables and carried out by one of the present authors (F. R. B.).