Sewage Disposal and River Pollution. 71 



objectionable, untouched. The lecturer proceeded — We now 

 come to what is termed the scientific or chemical treatment of 

 sewage. It may be stated briefly that natural laws, applicable 

 to liquid purification, are— First, subsidence ; second, natural 

 oxidation ; third, the general laws of chemical affinity — with 

 the latter is combined filtration. No matter how carried out, 

 chemical treatment aims at accomplishing one or other of the 

 effects natural to these laws. In precipitation or forced subsi- 

 dence, the agent used is generally lime. In the oxidation of 

 organic matter, permanganic acid, or salts of iron, we often used, 

 either with sulphate of alumina, or with lime. The A B C, or 

 alum, blood, and clay process, has been keenly fought over, 

 and is yet in controversy. The new process at Southampton 

 by which three grains of " very porous carbon " are added to 

 each gallon of sewage, probably effects little more than a partial 

 deodorisation of the liquid. Some other chemicals would seem 

 to operate quite as much by bleaching, as by really purifying 

 the sewage. But the bulk of these systems all aggravate the 

 difficulty of the "sludge" or solid deposit from the sewage by 

 adding, in the form of lime, alumina, or other ingredients, 

 immensely to its bulk, and none of them are carried out except 

 at great cost. The Birmingham Drainage Board, for instance, 

 has ^400,000 invested in works (not sewers), and the sewage 

 treatment of London, in the manner proposed by Mr. Dibden, 

 is estimated to cost annually -£\ 18,000; another system 

 proposed, but not adopted there, contemplated an outlay of 

 3^ millions and an annual expenditure of ^198,000; whilst a 

 third proposal went as far as 3| millions, and ^"219,000 of an 

 annual expenditure. In attempting to describe the possible 

 future aspect of sewage disposal I may be allowed a little lati- 

 tude, but will avoid as far as possible merely theoretical con- 

 clusions. The main question depends on obtaining a system of 

 purification that shall be of universal application. If in so 

 doing we can minimise the cost, and so reduce the ratal burdens, 

 we shall have accomplished something ; if we can obtain a cheap 

 manure, we shall have benefited the largest industry in the 

 country. I am not going to tell you that i( Peruvian guano" 



