386 The Composition of Sewage, [July* 
understood many futile processes would never have been 
proposed, and if proposed would never have been enter- 
1 9 .insci • 
I will take first the simplest case, that of a “residential ” 
town. By this term sanitarians mean a town where few, if 
any, manufacturing operations are carried on, and where 
the liquid refuse is chiefly of domestic origin. As examples 
may be mentioned Oxford, Bury St. Edmunds, Leamington, 
Keswick, &c. The sewage of such towns is generally of a 
concentrated character, and the matters which it holds in 
suspension and solution are for the most part of an organic 
and a readily putrescible character. It contains the solid 
and liquid excretions of the inhabitants, the urine of horses 
and cattle discharged in the streets, the drainage of stables, 
piggeries, &c., the blood (more or less) of the cattle killed 
in the town, and the washings of slaughter-houses. Another 
important constituent is the water which has been used for 
washing the persons of the inhabitants, their clothing, their 
cooking utensils, &c. These slops, as they are called, are 
very offensive ; they hold in suspension and solution soap, 
fatty acids, the juices of meat and vegetables, and the 
exudations from the human skin. Almost everyone must 
have observed that if a bowl of suds from “ washing day 
has been allowed to stand, it gives off in a very few hours a 
most unpleasant odour. There are also certain organic sub- 
stances not offensive, nor readily capable of putrefaction, 
but which nevertheless play a very important part as far as 
the treatment of sewage is concerned. Thus a very large 
quantity of waste paper finds its way into the sewers, and 
is there subdivided into particles which quite escape the 
notice of an inexperienced observer. To these are a.dded 
fine filaments derived from washing linen and cotton articles, 
and to a less extent from woollens. I say to a less extent, 
not because woollens when washed give off a smaller quan- 
tity of fibre, but because the total amount of woollens 
washed in a residential town is much smaller than that of 
cotton and linen fabrics. These filaments of textile mate- 
rials and of paper are scarcely perceptible on a hasty 
examination. A glass of sewage, held up to the light, if 
not rendered turbid by suspended clay, road-silt, &c., appears 
almost as limpid as ordinary river- or pond-water. But if 
we attempt to filter it through the filter-paper used by che- 
mists we find that the flow, though tolerably rapid at first, 
is quickly retarded, and before long comes practically to an 
end. If the liquid is then carefully poured away from the 
filter-paper, and a small portion of the latter is examined 
