Cholera infantum from impure water, 226. Cholera, in Hamburg from water, 230. caused by water, 214. Clarification, definition of, 113. Clark, H. W., 24, 190. Clark’s process for softening water, 92, 145. Clay particles, size of, 123. Cleaning filters, 68. Coagulant, absorption of, by suspended matters, 154. successive applications of, 154. Coagulants used in practice, 150. Coagulation of waters, 144. Cologne, water-supply of, from wells, 276. Color, 113. amount of coagulant required to remove, 153. amount of, in various waters, 115. measurement of, 114. Color, removal of, 117. Continuous filters, 5. filtration, nature of, 83, 92. Cost of filters and filtration, 4, 48, 102, 200, 314. Covered filters, efficiency of, 17. Covers for filters, 12, 15. at Albany, 295. in the United States, 17. omitted at Lawrence, 101. Crenothrix, 105, 186. Diarrhœa from impure water, 226. Dibden, W. J., 129. Disease from water, 210. Double filtration at Schiedam, 273. Drainage areas of a number of rivers, 133. Dresden, water-supply of, from filter-gallery, 276. Drown, Dr. Thomas M., 150, 191. Effective size of sand, 21, 238. European sands, 25. Efficiency of filtration, 83, 88, 91. effect of rate upon, 50. effect of size of sand-grain upon, 30. effect of thickness of sand layer upon, 34. at Lawrence, 106. European filters, 91, 260. Effluents, wasting after scraping, 74. Fæces, number of bacteria in, 215. Far Rockaway, L. I., filters at, 193, 253. Filling sand with water from below, 68, 307. Filter beds, bottoms of, must be water-tight, 12. covers for, 12. form of, 11. size of, 10. Filters, aggregate capacity of, 254. depths of waters on, 45. list of cities using, 244. reserve area required, 47. first constructed at London, 83. for household use, 183. general arrangement of, 6. Filters, statistics of, at various cities, 241. Filtration, cost of, 200. degree of purification required, 5. general nature of, 92. Fischer tile system, 181. FitzGerald, Desmond, 73, 111, 196. Flood flows not taken for supply, 10. Fränkel and Piefke, experiments on removal of disease germs, 86. Frankfort on Main, water supply of, from springs, 276. Frankland, Dr. Percy, 84. Friction of filtered water in pipes, 264. water in gravel, 37. water in sand, 22. water in underdrains, 40. Frost, effect of, upon filters, 12, 229, 266. Frühling, on the heating of water by sunshine, 16. underdraining at Königsberg, 39.