64 A Solution of the Sewage Problem. [January, 



may nevertheless be coloured. These residual impurities 

 are attacked by the charcoal : the powerful affinity of animal 

 charcoal for organic colouring matter corrects the one evil, 

 whilst the well-known absorptive action exerted by vegetable 

 charcoal on the gaseous products of putrefaction corrects 

 the other. In the way of purification little more remains 

 to be done. 



These reactions, by a modification in the order in which 

 the purifying ingredients are added, are effected at once, 

 with a certainty of uniform results, and, by a simple me- 

 chanical arrangement, variation in the dose of each con- 

 stituent required by a variation in the strength of the sewage 

 can be readily controlled. 



The method of applying the ingredients is extremely 

 simple. The clay and charcoal are incorporated in a 

 grinding mill with the aid of sufficient water to form a 

 thin paste. This paste flows into a tank, and is constantly 

 agitated until it is required to be mixed with the 

 sewage. By the side of the mixing-room is a smaller room, 

 through which passes a channel or trough. At one end of 

 this channel there rushes in the London sewage, and with 

 it an unmistakable odour. The B C mixture or thin 

 water-paste of clay and charcoal is admitted to the trough 

 by a pipe from the store-tank ; the sewage in its passage 

 past this pipe carries with it the mixture, and the two after 

 well mixing proceed on their way past a second pipe con- 

 nected with a tank containing a supply of sulphate of 

 alumina dissolved in water. All that is now requisite is to 

 allow the sewage, B C mixture, and alum to flow in inodorous 

 company to the settling tanks. The channel leading to the 

 tanks has its course interrupted by numerous ledges, which 

 serve to cause the more perfect intermixture of the sewage 

 and the disinfectants. The first tank in which the sludge 

 is allowed to settle contains the principal portion of the 

 precipitate. The clear water is allowed to flow off con- 

 tinuously from the first tank into a second tank ; and the 

 remainder of the mud is deposited in this and in the other- 

 tanks into which it flows. From the last tank the water is 

 conducted to the river, appearing as a clear, inodorous, and 

 tasteless effluent. When sufficient sludge has been collected 

 in the first tank, the treated sewage is shut off from this, 

 and permitted to flow into another tank, which then forms 

 the first of the series. As much of the water as possible 

 is then run off from the mud, and the latter is drawn into 

 the acidifying tanks, where a small quantity of sulphuric 

 acid is added to prevent the loss of any ammonia. From 



