PREFACE TO THE THIRD EDITION.

The lamented death of the talented Author of the ‘Treatise on Coal-Gas’ rendered itnecessary to appoint an Editor to prepare for the Press the new edition, which had beenfor some time demanded; and the numerous improvements in gas-engineering, and ingas-apparatus generally, since the appearance of the last edition, made the task of adaptingthe Work to the present advanced state of knowledge one of no ordinary difficulty.

Though the fundamental portions of the Second Edition have been retained, they havebeen enlarged and adapted to existing circumstances, and several new Chapters have beenadded to give fuller development to processes that were imperfectly understood when theformer editions were published. Among the subjects that have been greatly extended, theapplication of clay retorts is the most important; and for the further illustration of thatimprovement in the manufacture of coal-gas, numerous additional plates and woodcutshave been introduced. The employment of exhausters, rendered necessary by the use ofclay retorts, the new processes of purification, the improvements in gas-holders, in con-sumers’ meters, in burners, and in the measurement of the illuminating power of gas, havealso required that the portions of the Second Edition relating to those matters should berewritten, and considerably increased. The new Chapters are those on the Analysis ofCoal, on Clay and Brick Retorts, Exhausters, Purification, Consumers’ Meters, Regulators,Photometry, and on Residual Products. By these additions the Work has been enlargedabout one-third, and the number of plates and woodcuts has nearly been doubled.

E. C. B.

Hampstead , September. 1859 .