344 
Sewage Disposal and Rivers Pollution. 
of people, had not a single acre experimented upon for sewage puri- 
fication, was corrected by the statement that Mr. Crimp (late of 
Wimbledon) has now under the London County Council just laid 
out one acre for the purpose ; we are also told that experiments 
on the filtering process of different materials are now being carried 
out for the London County Council. These are, at any rate, signs 
of awakening, and with a few lines stating the present position of 
the Metropolitan area we may pass on to review what is being 
done elsewhere. 
A partially successful though costly remedy for the filthy con- 
dition of the Thames, which had literally become intolerable, has 
been found by a rough clarification of the sewage at the outfalls at 
Barking and Crossness by chemical precipitation. To each gallon 
is added about 4 grains of lime and 1 grain of sulphate of iron, which 
produce a rapid settlement of the grosser suspended matters in the 
form of slime or sludge. From 2 to 2\ million tons of this sludge 
are scraped off the settling tanks, pumped into barges, and sent 
out to sea annually, and to that extent the effluent discharged into 
the river is of course purified. The quantity of chemicals used is 
the minimum that will produce anything like clarification when the 
sewage happens to be of the quality experimented on by those 
who prescribed the dose. Less would not clarify, more would 
mean more cost and more sludge. But, alas ! sewage is not 
always of this ideal quality, and so it is to be feared the clari- 
fication is often A r ery incomplete. To render the effluent more 
presentable it is therefore dosed with a little of what is practically 
Condy’s Disinfecting Fluid (manganate of soda and sulphuric acid 
are the materials actually used) before discharge into the river ; 
this, too, is a very costly business, and the success again very 
partial, a small fraction only of the putrefiable matter being 
destroyed by the disinfectant, and the disinfection, therefore, merely 
temporary. The net result is that there is some improvement 
in the condition of the river at the outfalls, though the mass of 
impure effluent discharged into it still pollutes to a very undesir- 
able extent, especially during such a season as the summer of 
last year. A significant remark was made by Mr. Cooper — 
“that the effluent of the London sewage into the river Thames 
should be much more largely diluted, he thought, was quite 
impossible. The water supply was, he thought, something like 
one-third of the amount of water coming down the river in dry 
seasons.” Unless, therefore, the metropolitan authorities can deal 
successfully with their enormous effluent from the sludge tanks by 
filtration through soil, sand, or prepared purifying material, there 
is much justification for those who hold that ultimately the sewage 
of London will have to be removed bodily .to the Mapplin Sands 
or some more suitable distant spot. 
Towards the possibility of purifying by filtration the partially 
clarified effluent on the scale required for the enormous output of 
London little attention has hitherto been directed, and until 
recently no experiments worthy of the name seem to have been made. 
