arrels of 300 pounds each." (_Chapin, Mun. San. in U. S._)

=The Immediate Disposal of Sewage.=--The final disposition of sewage
is only one part of the problem of sewage disposal; the other part is
how to remove it from the house into the street, and from the street
into the places from which it is finally disposed.

The immediate disposal of sewage is accomplished by two methods--the
so-called _dry_, and the _water-carriage_ methods. By the _dry method_
we mean the removal of sewage without the aid of water, simply
collecting the dry and liquid portions of excreta, storing it for some
time, and then removing it for final disposal. By the _water-carriage
method_ is understood the system by which sewage, solid and liquid, is
flushed out by means of water, through pipes or conduits called
sewers, from the houses through the streets to the final destination.

=The Dry Methods.=--The dry or conservacy method of sewage disposal is
a primitive method used by all ancient peoples, in China at the
present time, and in all villages and sparsely populated districts; it
has for its basic principle the return to mother earth of all excreta,
to be used and worked over in its natural laboratory. The excreta are
simply left in the ground to undergo in the soil the various organic
changes, the difference in methods being only as regards the vessels
of collection and storage.

The methods are:

(1) Cesspool and privy vault.
(2) Pail system.
(3) Pneumatic system.

_The Privy Vault_ is the general mode of sewage disposal in villages,
some towns, and even in some large cities, wherever sewers are not
provided. In its primitive and unfortunately common form, the privy
vault is nothing but a hole dug in the ground near or at some distance
from the house; the hole is but a few feet deep, with a plank or rough
seat over it, and an improvised shed over all. The privy is filled
with the excreta; the liquids drain into the adjacent ground, which
becomes saturated, and contaminates the nearest wells and water
courses. The solid portion is left to accumulate until the hole is
filled or the stench becomes unbearable, when the hole is either
covered up and forgotten, or the excreta are removed and the hole used
over again. This is the common privy as we so often find it near the
cottages and mansions of our rural populace, and even in towns. A
better and improved form of privy is that built in the ground, and
made water-tight by b