Transcriber’s Notes: The spelling, hyphenation, punctuation and accentuation are as the original, except for apparent typographical errors which have been corrected. Italic text is denoted _thus_. Bold text is denoted =thus=. See further notes at the end of the book. [Illustration: GENERAL VIEW OF FILTERS AT HAMBURG. [_Frontispiece._] ] THE FILTRATION OF PUBLIC WATER-SUPPLIES. BY ALLEN HAZEN, MEMBER OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS, THE BOSTON SOCIETY OF CIVIL ENGINEERS, THE AMERICAN WATER-WORKS ASSOCIATION, THE NEW ENGLAND WATER-WORKS ASSOCIATION, THE AMERICAN CHEMICAL SOCIETY, THE AMERICAN PUBLIC HEALTH ASSOCIATION, ETC. _THIRD EDITION, REVISED AND ENLARGED._ SECOND THOUSAND. NEW YORK: JOHN WILEY & SONS. LONDON: CHAPMAN & HALL, LIMITED. 1905. Copyright, 1900, BY ALLEN HAZEN. ROBERT DRUMMOND, ELECTROTYPER AND PRINTER, NEW YORK. PREFACE TO FIRST EDITION. The subject of water-filtration is commencing to receive a great deal of attention in the United States. The more densely populated European countries were forced to adopt filtration many years ago, to prevent the evils arising from the unavoidable contaminations of the rivers and lakes which were the only available sources for their public water-supplies; and it has been found to answer its purpose so well that at the present time cities in Europe nearly if not quite equal in population to all the cities of the United States are supplied with filtered water. Many years ago, when the whole subject of water-supply was still comparatively new in this country, filtration was considered as a means for rendering the waters of our rivers suitable for the purpose of domestic water-supply. St. Louis investigated this subject in 1866, and the engineer of the St. Louis Water Board, the late Mr. J. P. Kirkwood, made an investigation and report upon European methods of filtration which was published in 1869, and was such a model of full and accurate statement combined with clearly-drawn conclusions that, up to the present time, it has remained the only treatise upon the subject in English, notwithstanding the great advances which have been made, particularly in the last ten years, with the aid of knowledge of the bacteria and the germs of certain diseases in water.