This is made in several forms by the firm of John Matthews, New York. It is connected with the main at A, and with the distributing pipe at B. The case D is filled with a layer of sand and a layer of charcoal which are held in place by a wire sieve on top and bottom of D. This case is inserted into the body of the filter directly over the distributing pipe. The diameter of this case is smaller than that of the body of the filter; an annular space is therefore left between the two in which the impurities may settle. In the top of the filter is a semi-globular chamber containing a quantity of sponges. The object of these sponges is to arrest coarse matter such as gravel, sticks and straw, so that the water reaches the sand and charcoal layers in a comparatively clean state.

Fig. 14.   The Bigelow Curtis Filter

Fig. 14. - The Bigelow-Curtis Filter.

In order to clean the filter, turn off the supply cock A, unscrew the thumbscrews which hold the cover fast, take off the cover, remove the sponges and wash them out thoroughly; then reverse the sand and charcoal cup, replace the sponge and cover, shut off the cock B, open the waste cock C, and open the cock A. When the water discharged through C runs pure and clear, close the cock C and open the cock B.