SEPTIC TANK

a container for receiving and purifying sewage. The succe ful operation of the tank depends upon bacterial action. The tank, or that portion of it in which purification occurs, is kept perfectly dark and airtight. These conditions favor the growth of a bacterium known as the Anaerobiosis, which has the power of rendering sewage liquid and odorle . In practice, it is the custom to make use of a catch basin through which washing water is pa ed in order to catch soaps and greases. Water from the toilet, however, pa es directly into the tank. The latter is usually divided into two compartments the first being known as the liquefying chamber, the second as the effluent chamber. The greater part of the bacterial action occurs in the liquefying chamber, so that this is usually constructed at least four times as large as the effluent chamber. A crust or scum forms upon the top of the sewage in the first compartment, which serves to exclude air and so favors the growth of the anaerobic bacteria. This bacterial growth also produces sufficient heat to revent freezing in winter. When the iquid in the first compartment rises above a certain level, it flows into the second compartment where further bacterial action takes place. The effluent from this compartment is caused to travel through a loosely laid drain buried in cinders, sand, gravel, or other porous material. Where the system is installed, care should be taken to avoid the use of chloride of lime or other antiseptics or deodorants, as these tend to kill the bacteria and so check the purifying action. It is stated that a properly constructed system will function without attention for several years, the effluent being inoffensive and harmle . See also SHWAGE.