SEPTIC TANK EXPERIMENTS. _Rate of Flow and Deposition of Suspended Matters._ -----+------------+-----------------------+ | | Rate of Flow. | | +-----------------------+ | | | | No. | Name of | Length of | Velocity | | Town. | Sojourn | of Flow | | | of Sewage | per | | | in Tank. | minute. | | | | | -----+------------+-----------+-----------+ | | | | | | days. | inches. | 1 | Exeter | 1·0 | 0·52 | | | | | 2 | Manchester | 0·44 | 5·58 | | | | | 3 | “ | 0·56 | 4·44 | | | | | 4 | Leeds | 0·5 | 1·68 } | | | | | 5 | “ | 1·0 | 0·84 } | | | | | 6 | “ | 2·0 | 0·42 } | -----+------------+-----------+-----------+ -----+----------------------------------------------- | Suspended Matters in Sewage. |-----------+-----------+------------+---------- | | | | No. | Remaining | Destroyed | Leaving | | in | and | Tank | Total. | Tank. | Liquefied | in | | | in Tank. | Effluents. | | | | | -----+-----------+-----------+------------+---------- | | | | | per cent. | per cent. | per cent. | 1 | 17 | 39 | 44 | 100 | | | | 2 | 41 | 22 | 37 | 100 | | | | 3 | 23 | 33 | 44 | 100 | | | | 4 | .. | .. | .. | .. | | | | 5 | average | 28 | .. | .. | say | | | 6 | | .. | .. | .. -----+-----------+-----------+------------+---------- [Sidenote: Septic tanks reduce the sludge difficulty to some extent, but do not altogether remove it.] (_e_) _Destruction and Liquefaction of Sludge in Septic Tanks._—It was formerly maintained that the employment of a septic tank did away with all sludge difficulties, and one sees even now advertisements to that effect, that there is “no sludge” with a septic tank; but experience everywhere does not bear out this contention. On the contrary, there must be sludge with a septic tank, and the only question one has to consider is, to what extent does a septic tank reduce the quantity of sludge?