seriously taking in hand the work of saving our rivers and streams from pollution, and the question is constantly being asked, "What is the best process of sewage purification to adopt?" The form of this question shows only too clearly that the real nature of the problem is not generally understood. It is, indeed, of the first importance that members and officers of the various bodies, upon whom devolves the duty of dealing with the problem of purification of sewage, should grasp the scientific principles of the question, and recognize the fact that the particular scheme to be adopted in any locality must depend upon a variety of local circumstances. It is with the view of giving some help in this direction that the following pages have been written.
During recent years, by means of numerous bacteriological and chemical investigations, both in this country and in America, great advances have been made in our knowledge of the changes which sewage undergoes in purification, and not a few conclusions of widereaching importance established; and it is hoped that the presentation in this little work of some of the results thus attained will be found useful by engineers and other officials who wish to avail themselves of the latest researches of chemists and biologists upon the question of Sewage Purification.