For a long outfall sewer with no connections this method has many advantages, notably so in the large furnace and shaft erected on the Brighton outfall sewer by the borough surveyor, Mr. Lockwood. But in a general system of sewerage, it was found by experiments made by Sir Joseph Bazalgette, C.B. that the effect of trying to reduce the gases by the action of furnaces was but very small, and that the area over which the effect extended was but very limited: in fact, a sewer may be compared to a perforated tube, the house drains, gully drains, &c., representing the perforations; the effect of an exhaustion by the action of the furnace is simply to suck fresh air into the sewer at all these points instead of removing the foul air for any distance. High shafts at different points effect a partial clearance of sewer gases, but they are very costly, and the reasons I have previously given against the system of open shafts are practically the same in this and all other modifications of the principle. Many other methods have been tried from time to time, either to prevent the formation of gases in the sewers, or neutralize or destroy them, some of which are as follows: By giving a quick velocity of discharge in a sewer; by placing materials within sewers which would absorb the gases as fast as they were generated; by passing deodorants or disinfectants into sewers; by deodorizing or disinfecting all materials before they are allowed to enter a drain or sewer; by placing chemical agents within sewers to give off certain gases which would then, it was conjectured, destroy the noxious properties of the sewer gases; by introducing charcoal into sewers to absorb the foul gases; by laying pipes within the sewers for the purpose of discharging chlorine into the sewer; by employing galvanic agency to disengage or to produce ozone from the sewer gas; by passing the foul air through shafts into which water was constantly injected, and by endeavouring to extract the foul air by fans driven by machinery. I have myself patented a plan for “annihilating sewer gases” by allowing them to be absorbed into dry earth, and have tried the system with some very marked and successful results.[195] Having thus far considered all the known methods for dealing with the noxious emanations which proceed from sewers, the next point to consider is what these noxious emanations are, and whether they exist in all sewers.