SEWAGE DISPOSAL 347 
inch gas pipe as shown in Fig. 73. The liquid is with- 
drawn from a point near the middle of the tank as in-- 
dicated by the discharge pipes. The eight-inch space 
above the discharge permits the accumulation of organic 
matter. The discharge from 'B into C, is the same as 
that from A into B; but the discharge pipes are of neces- 
sity lower by an amount indicated by the dotted lines. 
Compartment C discharges intermittently by means of 
an automatic syphon. 
The sewage becomes gradually purified in its passage 
through the tank, and as it flows from the last section 
it is nearly as clear as water, but has a slightly sour odor, 
which it seems to retain and which is in no way objection- 
able. The purified sewage has been kept for weeks with 
no sign of the development of putrefactive odors. 
The discharges should be arranged as shown in Fig. 
65. This arrangement will cause the least mixing of old 
and new sewage. There is no discharge from A into B 
until the second day’s sewage flows into A. Similarly 
there is no discharge from B into C until the second 
discharge into B, etc. The sewage, therefore, requires 
from three to four days in its passage through the tank. 
Cost of Septic Tank. A double partition tank, 12 
feet square and 4% feet deep, constructed of concrete 
consisting of one part cement, two parts sand and four 
parts gravel, will cost approximately $50.00 when the 
walls are five inches thick. 
SEWAGE DISPOSAL FROM DWELLING. 
The open privy and the cesspooi of kitchen slops are 
objectionable not only in so far as they affect the dairy 
house, but also in that they constitute a source of danger 
to the members of the family in ways entirely discon- 
nected with the milk supply. With the dairy house 
