256 Prof. Hosking on Ventilation. 
from the matters which go with, or have gone before, the hot 
water ;. and with these gases house-drains almost always, and 
sewers commonly, stand charged. They are light fluids and do 
not go down with the heavy liquid matters from which they 
have been evolved, but they seek to rise, and constantly do rise 
in almost every house through imperfections or derangements of 
‘the flaps and traps which are intended to keep them down, but 
which only, when they do act, compel some of the foul air to 
enter the sewers, and there to seek outlet to the upper air which 
they find by the gulley gratings in the streets. 
It can hardly be said perhaps that too much attention has been 
given of late to the scour of sewers by water; but it is most cer- 
tain that too little attention has been given to the considerations 
last stated, for nothing has been done to relieve the drains and 
sewers of their worst offence. 'The evolution of foul and nox- 
10us gases in the drains is certainly not prevented by scouring 
the sewers. In the meantime the poison exists under foot, a 
exudes at every pregnable point within and about our houses, 
and it rises at every grating in our streets, though the senses may 
of mines, and particularly of coal mines. An up-cast shaft con 
powiie a common chimney flue carried up at the back of every 
sewers would carry with it much soot and fine dust, which ruin 
settle upon the liquid current and pass off with it, and so — 
_the tangible as well as the intangible impurities, befi 
this aur age streets and about 8 gent in 
way might be effected by the aid of ca 
constant ion: a : were 
also a dition but if the up-cast shaft to every house 
rains fi ini : a] air would be 
thrown off into Wiecgenien foul air, but the foul air wot 
innocuously and witho ‘ng as it now 
does from the se out offence instead of steaming as 
Wers into the air where it cannot be avo 
