This filter consists of an external metal case, inside of which is a perforated metal pan resting on a circular flange, at a sufficient height above the bottom of the filter to leave reservoir space for the filtered water. On this pan, which is shaped like an inverted cone, is a layer of gravel reaching about four inches above the edge of the pan. Then come alternate layers of charcoal and gravel, about six inches deep, to within about ten inches of the top of the filter, with a thin layer of sand over the last layer. A float valve attached to the inlet pipe regulates the supply of water. This filter should be cleaned, and the charcoal renewed, whenever it fails to do its work thoroughly. It is manufactured by the firm of John Matthews, New York.

Fig. 14.   The Tank Filter

Fig. 14. - The Tank Filter.