----+--------------------------+----------------------+---- |Internal diameter of pipe.|Thickness of material.| +--------------------------+----------------------+ | in. | in. | | 3 | ¹⁄₂ | | 4 | ⁵⁄₈ | | 6 | ³⁄₄ | | 9 | 1 | | 12 | 1¹⁄₈ | | 15 | 1¹⁄₄ | | 18 | 1³⁄₈ | ----+--------------------------+----------------------+---- The thickness of fire clay or earthenware pipes should be slightly in excess of those given for stoneware. [185] The patent automatic flushing arrangement by Mr. Rogers Field, C.E., is an excellent apparatus for lessening the chances of a sewer becoming choked from this cause. [186] It is necessary in many towns where the combined system is in force, and the sewage has to be pumped when heavy rains commence, to put temporary clay dams round the street gratings to prevent the surface water from entering the sewers, thus at once showing the inability of the system to deal with flood waters. CHAPTER XXI. SEWAGE DISPOSAL. The magnitude of the question of “sewage disposal” almost decided me to refrain from making any remarks upon it, but on reconsideration I thought a few might be serviceable. Sewage disposal means the getting rid of the foul water contained in the sewerage system of any community. Where a dry method is in force for the collection of the excrementitious matters it is called “interception”; the following are some of the systems which effect it:-- Privies, ashpits, middens, cesspools, pails, troughs, the “Rochdale,” the “Eureka,” the “Goux,” Fosses Permanentes, Fosses Mobiles, and Moule’s, Taylor’s, and Phillip’s earth closets. The collection and disposal of the mass of excrement under these dry systems is found to be a very troublesome matter, and they are at their best but inferior substitutes for water carriage, nor must it be forgotten that sewers and drains are necessary even if a good interception process is in force. I shall therefore confine my remarks to the disposal of water-carried sewage. Many books have been written, many valuable reports have been prepared and issued, lengthy papers and discussions have been frequent at the meetings of scientific societies, and almost innumerable pamphlets have been published upon this important sanitary subject. Some millions of money have also been spent in trying to deal satisfactorily with this question, not only with a view to the purification of the effluent of the sewage, but also to endeavour to make a profit out of the residuals.[187] The result of this literature, discussion, and experiment has led to the following conclusions: