box is not placed in
contaminated soil or where it may become filled with stagnant or
polluted water.--EDITOR.

[17] See Chapter XI for practical notes on cost of installation of
these three conveyed systems--hot-air, hot-water, and steam.--EDITOR.

CHAPTER IV

=Disposal of Sewage=

=Waste Products.=--There is a large amount of waste products in human
and social economy. The products of combustion, such as ashes,
cinders, etc.; the products of street sweepings and waste from houses,
as dust, rubbish, paper, etc.; the waste from various trades; the
waste from kitchens, e. g., scraps of food, etc.; the waste water from
the cleansing processes of individuals, domestic animals, clothing,
etc.; and, finally, the excreta--urine and faeces--of man and animals;
all these are waste products that cannot be left undisposed of, more
especially in cities, and wherever a large number of people
congregate. All waste products are classified into three distinct
groups: (1) refuse, (2) garbage, and (3) sewage.

The amount of _refuse_ and _garbage_ in cities is quite considerable;
in Manhattan, alone, the dry refuse amounts to 1,000,000 tons a year,
and that of garbage to 175,000 tons per year. A large percentage of
the dry refuse and garbage is valuable from a commercial standpoint,
and could be utilized, with proper facilities for collection and
separation. The disposal of refuse and garbage has not as yet been
satisfactorily dealt with. The modes of waste disposal in the United
States are: (1) dumping into the sea; (2) filling in made land, or
plowing into lands; (3) cremation and (4) reduction by various
processes, and the products utilized.

=Sewage.=--By sewage we mean the waste and effete human matter and
excreta--the urine and faeces of human beings and the urine of domestic
animals (the faeces of horses, etc., has great commercial value, and is
usually collected separately and disposed of for fertilizing
purposes).

The amount of excreta per person has been estimated (Frankland) as 3
ounces of solid and 40 ounces of fluid per day, or about 30 tons of
solid and 100,000 gallons of fluid for each 1,000 persons per year.

In sparsely populated districts the removal and ultimate disposal of
sewage presents no difficulties; it is returned to the soil, which, as
we know, is capable of purifying, disintegrating, and assimilating
quite a large amount of organic matter. But when the number of
inhabitants to the square m