In preparing an English edition of Prof. Fierz-David's well-known work on the practical side of dye chemistry, advantage has been taken of the opportunity to correct one or two slight errors that had crept into the original Swiss edition, and to make an alteration to Plate XV. For the rest, the book remains practically unaltered.

In most cases the original weights and prices have been retained (in francs per kilo.), instead of trying to convert them into shillings per pound. It was felt that, as the figures referred usually to prewar conditions in Switzerland, and having regard to the present unsettled state of the exchanges and of production costs, no good purpose would be served by attempting to give the English equivalents which, in any case, would in all probability only be misleading.

I wish to acknowledge, with much gratitude, the assistance rendered by my wife during the translation; and to Mr. C. Hollins my best thanks are due for his kindness in giving much valuable help in revising the manuscript and the proofs.

F. A. Mason.