HOUSE AND GARDEN 
January, 1912 
more easily, the rate can be in¬ 
creased. Thus', with an artificial 
bed made of gravel or broken 
stone whose particles are all about 
the size of peas, the sewage can 
be applied at nine times the rate 
given above, or, one square yard 
will serve for three persons. If 
the artificial soil is made up of 
stones as large as hickory nuts, 
two hundred gallons may be ap¬ 
plied daily to each square yard, 
or, one square yard will serve for 
six persons. 
The second requirement is se¬ 
cured by discharging the sewage 
onto the beds at intervals, the 
number of doses per day depend¬ 
ing on the size of the particles in the bed. Thus it is customary 
to run the proper dose onto a sand bed three times a day, making 
each dose one-third of the total daily amount. As the size of the 
constituent particles 
in the soil increases, 
the amount of the 
dose must be de¬ 
creased and the fre- 
ciuency of the doses 
increased, in order to 
keep the beds effective 
and in good order. 
Thus with pea-gravel 
one hour intervals 
and doses of an 
amount equal to one 
twenty-fourth of the 
daily volume are re¬ 
quired. With nut 
gravel the three in¬ 
tervals between doses 
is shortened to five 
minutes and the 
amount of the dose is 
decreased to corre¬ 
spond. 
The third requirement is met by providing an additional area 
over that theoretically required and by shifting the flow occa¬ 
sionally onto this extra area. 
This can be done most econom¬ 
ically by dividing the regular 
area into three beds and then 
each day shifting the flow from 
bed to bed in regular rotation 
with eight-hour periods of flow 
on each part. If the additional 
area is made equal to one of 
these parts, it is a simple matter 
to have three beds always work¬ 
ing and one always resting. By 
letting each quarter rest one 
day in four, the greatest possi¬ 
ble life is secured for the plant. 
A certain difficulty has been 
found in operating a plant as 
described from the fact that 
there is present in fresh sewage 
a certain amount of greasy, 
slimy matter which tends to 
clog the surface of the disposal 
beds, so that, even with intermit¬ 
tent treatment and alternate use 
the air cannot penetrate to the in¬ 
terior of the beds, and a treatment 
otherwise properly designed thus 
becomes a source of annoyance 
and the process a failure. In or¬ 
der to avoid such surface clog¬ 
ging. it is customary to run the 
sewage through a tank with a 
trapped inlet and outlet, thereby 
removing both the grease and a 
large part of the solids carried. 
Such a tank should hold from one 
to two days’ flow—that is, for a 
family of ten persons, using water 
at the rate of thirty gallons each 
per day, the tank should have a capacity of from three hundred 
to four hundred gallons. Three hundred gallons is forty cubic 
feet, so that a tank three feet wide, three feet deep and five feet 
long would fulfil the 
requirements. It has 
been thought that, since 
there has been found 
to be a certain disin¬ 
tegrating action going 
on in this tank, merely 
passing sewage through 
such a tank would con¬ 
stitute a purification 
process. Under the 
name of septic tank 
m any extravagant 
claims have been made 
for its usefulness, some 
writers even going so 
far as to say that by 
passing through such a 
tank the foulest sewage 
would be converted in¬ 
to the equivalent of 
spring water. But such 
claims cannot be sub¬ 
stantiated in practice, and the most that such a tank can do is to 
hold back grease and to diminish somewhat the quantity and to 
modify partially the character 
of the suspended solids, the lat¬ 
ter action being due to the bac¬ 
teria in the tank itself. It is de¬ 
sirable, in order to serve its ca¬ 
pacity, to clean out the tank 
once a year, although there are 
instances of tanks going five or 
six years untouched. In such 
cases it will usually be found 
that the tank has filled up to 
such an extent that no deposits 
take place as the sewage hur¬ 
ries through the tank in the 
small channel that the accumu¬ 
lated solids have left. During 
the first month of operation the 
tank may smell, so that it is 
desirable to put it underground 
and provide no ventilation. 
{Continued on page 62) 
In the filter bed the wooden troughs spread the liquid evenly 
over the sand. The walls slope so that the filtered liquid 
may be drained off from the bottom of the excavation 
At the extreme left of the drawing is the man-hole which can regulate the flow from 
one set of trenches to the other 
Where broken stone or gravel is used the inlet pipe is divided into 
two lines on the surface of the stone. The sewage is discharged 
from openings in the bottom of these pipes 
