Capacity of Filters 254 V. LONDON’S WATER-SUPPLY 255 VI. THE BERLIN WATER-WORKS 261 VII. ALTONA WATER-WORKS 265 VIII. HAMBURG WATER-WORKS 269 IX. NOTES ON SOME OTHER EUROPEAN WATER-SUPPLIES 272 The Use of Unfiltered Surface-waters. 275 The Use of Ground-water. 276 X. LITERATURE OF FILTRATION 277 XI. THE ALBANY WATER-FILTRATION PLANT 288 Description of Plant. 289 Capacity of Plant and Means of Regulation. 308 Results of Operation. 314 Cost of Construction. 314 INDEX 317 UNITS EMPLOYED. The units used in this work are uniformly those in common use in America, with the single exception of data in regard to sand-grain sizes, which are given in millimeters. The American units were not selected because the author prefers them or considers them particularly well suited to filtration, but because he feared that the use of the more convenient metric units in which the very comprehensive records of Continental filter plants are kept would add to the difficulty of a clear comprehension of the subject by those not familiar with those units, and so in a measure defeat the object of the book. TABLE OF EQUIVALENTS. Unit. Metric Equivalent. Reciprocal. Foot 0.3048 meter 3.2808 Mile 1609.34 meters 0.0006214 Acre 4047 square meters 0.0002471 Gallon[1] 3.785 liters 0.26417 1 million gallons 3785 cubic meters 0.00026417 Cubic yard 0.7645 cubic meters 1.308 1 million gallons per } { meter in depth } acre daily } 0.9354 { of water daily } 1.070 ACKNOWLEDGMENT. I wish to acknowledge my deep obligation to the large number of European engineers, directors, and superintendents of water-works, and to the health officers, chemists, bacteriologists, and other officials who have kindly aided me in studying the filtration-works in their respective cities, and who have repeatedly furnished me with valuable information, statistics, plans, and reports.