[13] Samuelson’s translation of Kirkwood’s “Filtration of River-waters;” Lindley, Die Nutzbarmachung des Flusswassers, _Journal für Gas- u. Wasserversorgung_, 1890, 501; Kaiserlichen Gesundheitsamt, Grundsätze für die Reinigung von Oberflächenwasser durch Sandfiltration; _Journal für Gas- u. Wasserversorgung_, 1894, Appendix I. [14] Lindley, _Journal für Gas- u. Wasserversorgung_, 1890, 501; Grahn, _Journal für Gas- u. Wasserversorgung_, 1890, 511; Halbertsma, _Journal für Gas- u. Wasserversorgung_, 1892, 686; Piefke, _Zeitschrift für Hygiene_, 1894, 151; and others. [15] Appendix I. [16] The Water Supply of Towns. London, 1894. [17] A special species of bacteria artificially added to secure more precise information in regard to the passage of germs through the filter. [18] _Zeitschrift für Hygiene_, 1894, p. 173. [19] Report Mass. State Board of Health for 1891, p. 438; 1892, page 409. [20] Appendix IV. [21] Piefke, _Zeitschrift für Hygiene_, 1894, p, 177. [22] _Journal für Gas- und Wasserversorgung_, 1887, p. 595. [23] _Zeitschrift für Hygiene_, 1894, p. 172. [24] Appendix IV. [25] Appendix I. [26] _Glaser’s Annalen_, 1886, p. 48; _Zeit. f. Hygiene_, 1889, p. 128. [27] _Vierteljahresschrift für öffentliche Gesundheitspflege_, 1891, p. 59. [28] _Journal für Gas- und Wasserversorgung_, 1891, 108. [29] _Zeitschrift für Hygiene_, 1894, 182. [30] I am informed that several other filters upon the same principle have been more recently built. [31] Report on Water Purification at Cincinnati, page 378. [32] Translation in German in Dingler’s Polytechnical Journal, 1832, 386. [33] Water Purification at Louisville, page 378. [34] Special Report Mass. State Board of Health 1890, Purification of Sewage and Water, page 747. [35] Water Purification at Cincinnati, p. 485. [36] Jour. of the New England Water Works Assoc., Vol. VIII, page 183. [37] Report of the Pittsburg Filtration Commission, 1899, page 55. [38] Rhode Island State Board of Health Report for 1894. [39] Report of the Rhode Island State Board of Health for 1894. [40] Report on the Investigations into the Purification of the Ohio River Water at Louisville, Kentucky. D. Van Nostrand & Co., 1898. [41] Ohio State Board of Health Report, 1897, page 154. [42] Report of the Pittsburg Filtration Commission, City Document, 1899. [43] Fuller, Water Purification at Louisville, page 425. [44] Warren, Feb. 9; June 1; July 6. Jewell, July 1; Feb. 9, 16, 17. [45] “Removal of Iron from Ground Waters,” Journal of the New England Water Works Association, Vol. xi, 1897, page 277. [46] Journal of the New England Water Works Association, Vol. ii, page 294. Description of plant by Supt. Lewis M. Bancroft.