64 KANSAS ACADEMY OF SCIENCE. 
clog the interstices of the sand and prevent the passage of water and the intro- 
duction of the needed air. But the method has found successful application on 
a practical scale for both sewage and water treatment. 
Stimulated by the necessities of their environment, the English people have 
been developing a line of treatment that perhaps more closely follows nature. In 
1896 the town of Sutton abandoned chemical precipitation, and installed Mr. 
Dibdin’s scheme of ‘‘contact beds.’’ In this the sewage, after a mechanical 
straining to take out the coarser solids, is run onto a bed of coarse burnt ballast, 
where it is held for a time, that it may deposit the suspended matter and be 
worked upon by the anaerobics, thus forming what is called the ‘‘contact.’’ The 
effluent from this ‘‘bacteria tank’’ is then run onto a bed of fine coke-breeze 
which is operated intermittently, with the intention of getting the action of the 
aerobics. 
The two tanks form a ‘‘double-contact’’ system. They are arranged in du- 
plicate, so that each pair has a period of rest and aeration. From this it seems 
that reliance is placed on aerobic filters and organisms for combined liquefaction 
and nitrification in the same bed. While the results are generally good, they are 
somewhat variable, the reason for which appears to be as follows: The two 
classes of organisms are mutually antagonistic; an excessive development of one 
excludes the other, so the true anaerobics do not have opportunity to become 
well established in the first tank because of its ‘‘resting empty’’ period, while 
those forms that can adapt themselves are under the necessity of changing their 
habits every few hours. A further result is that some organic matter is carried 
over to the second bed without undergoing the stage of change, thus forcing upon 
that bed some of the work that should have been done in the first. The whole 
bacterial process is thus frequently disturbed. There is also the screened sludge 
first taken out to be separately dealt with. 
In 1895 Mr. Cameron introduced at Exeter the ‘‘septic tank.”’ In this sys- 
tem the raw sewage as it comes from the mains is passed into an underground 
air- and light-tight tank of such capacity as to hold the flow of twenty-four hours. 
Both inlet and outlet are below the surface of the water, so that the gases formed 
do not escape and floating solids are retained. During the twenty-four hours 
that the sewage has to pass through it is attacked by the anaerobics, which find 
the conditions very favorable, with the result that all solids of whatever organic 
nature are broken up and largely dissolved. The heavier mineral matter is in- 
tercepted in a grit chamber adjacent to the tank before the admission of sewage. 
The surface of the tank is covered by a thick, tough scum, which catches and 
holds the lighter floating solids until they are broken up. On the bottom, there 
very slowly accumulates a deposit of mineral nature and organic matter that de- 
composes but slowly. After four years of use this deposit was only four feet 
thick, representing the total residue of the sewage of a population of 1500 people. 
The gases formed are inflammable and may be utilized, the pressure being ob- 
tained by raising the surface of the contents of the tank by changing the eleva- 
tion of its outlet, and confining the gas between this and the arched roof. 
The effluent from this ‘‘septic tank’’ is run over a weir in a thin sheet to 
aerate it and then discharged onto filter-beds of coke-breeze, where the nitrify- 
ing organisms do their work. Here, then, is a true separation of the two classes 
of bacteria, and the requirement of regular and continuous action is at Joast met 
in the first part of the process. 
You will remember, however, that there are three stages of action and three 
classes of bacteria at work before nitrates are reached. Triple-contact beds, or 
the addition of a third filter to the septic system, have been suggested as adapted 
