It is possible to err in both directions. A university professor, lecturing on higher Mathematics, is reported to have told his audience that it was a source of great satisfaction to him that the theorem which he was demonstrating could never be applied to anything “useful.” On the other hand, we have the well-authenticated story of the man who took his son to the Royal School of Mines to “learn copper,” and not to waste his time over other parts of Chemistry, because “they would be of no use to him.” For narrowness of outlook, there is nothing to choose between the pedant and the “practical” man. National education would deteriorate if its control should ever pass into the hands of extremists of either type, for nothing worthy of the name of education could ever be given or received in such an irrational spirit. In dealing with the subject of “Acids, Alkalis, and Salts,” I have endeavoured to give prominence to the commercial and domestic importance of the substances dealt with. I thereby hope to gain the interest of the reader, since interest stands in the same relation to education that petrol does to the motor-car. It is not education itself, but it is the source of its motive power. I have also included some considerations of a theoretical nature which may well be taken as a first step towards the continuation of the study of Chemistry. My sincere thanks are offered to my colleagues, F. W. G. Foat, M.A., D.Litt., and Mr. I. S. Scarf, F.I.C., for much valuable help and advice; to Sir Edward Thorpe, C.B., F.R.S., and Messrs. William Collins & Sons for permission to reproduce Figures 3, 11, and 14; to Messrs. Longmans & Co. for Figures 4, 5, 9, 12, 13, 16; Messrs. Macmillan & Co., for Figures 8, 10 and 15. I have also availed myself of the assistance of several standard works on Chemistry. My acknowledgments in this direction take the practical form of the short bibliography which follows— Lunge, Dr. G. _The Manufacture of Sulphuric Acid and Alkali._ Vols. I, II, and III. Roscoe & Schorlemmer _Treatise on Chemistry._ Vol. I. The Non-metallic Elements (1911). Vol. II. The Metals (1913). Brannt, W. T. _The Manufacture of Vinegar and Acetates._ Thorp, F. H. _Outlines of Industrial Chemistry_ (1913). Thorpe, T. E. _A Manual of Inorganic Chemistry._ Newth, G. S. _A Text-book of Inorganic Chemistry._ Mellor, J. W. _Modern Inorganic Chemistry._ Cohen, J. B. _Theoretical Organic Chemistry._ G. H. J. A. City of London School, E.C. CONTENTS