3-i 
BULLETIN 5' 
DEPAET3IEXT OF AGRICULTURE. 
,%^e-Cfesef 
hours gives the best results and the least annoyance. The solid 
matter settles out in such a tank and, according to the theory at 
present accepted, it is partially liquefied, deodorized, and destroyed 
by countless numbers 
of bacteria, which 
thrive in filth and live 
without air. Some 
authorities assert that 
these bacteria also 
slightly affect the dis- 
solved organic matter 
in raw liquid sewage. 
In such a tank a 
thick scum forms on 
the surface of the sew- 
age, which prot 
the bacteria from the 
incoming air and is 
evidence of good bac- 
terial action. The 
breaking up or dis- 
turbance of this scum 
will destroy the bac- 
terial acti n : r the 
time being and is 
likely to cause con- 
siderable annoyance 
by bad odors. 
FINAL TREATMENT. 
It is found that the 
septic tank effects 
only about 40 pel 
purih cation. The 
liquefying action in 
the tank, however, 
makes it possible to 
subject the sewage to 
a final treatment by 
nitration or distribu- 
tion in a natural soil, 
liiis final purification 
is effected by means of bacteria which work in the air. Therefore it is 
necessary the sewage be applied to the final disposal system in 
intermittent doses so that the system may have a chance to air out. 
To S e ,-r-S 
