IN the second edition, the general plan of this book lias been retained, but several chapters have been rearranged and partly rewritten. This revision has improved the utility of tho book. About fifty pages of new material have also been added. These include a discussion of heterogeneous solid gas equilibria, dealing with the carbon-oxygen reaction and its participation in the blast furnace; the methods of electrometric hydrogen ion determination and poten-tiometric titrations, which are very briefly dealt with; oxidation-reduction indicators, which are briefly but clearly explained; and a section on electrolysis which includes a discussion of over-voltage from the modern point of view.