Septic Tanks 115 



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Mouras "Automatic Scavenger," bacteriological purifi- 

 cation of sewage saw notable progress in other directions. 

 The fact that sewage may be partly purified by filtra- 

 tion through sand or other finely divided material, was 

 a matter of common observation. Yet it was believed 

 in the third quarter of the last century that the purifying 

 effect of such filtration was entirely mechanical and due 

 to the retention of the suspended matter by the filter. 

 Chemical analyses soon showed, however, that the 

 filtration process led to marked changes in the compo- 

 sition of the sewage. The opinion was expressed that 

 the finely divided material of the filter facilitated the 

 union of atmospheric oxygen with the constituents of 

 the sewage. 



At the beginning of the seventies, the study of micro- 

 organisms had made sufficient progress, and the work of 

 Pasteur had made an impression deep enough, to raise 

 the question in the minds of some as to the relation of 

 bacteria to the purification of water and sewage. In 

 1877, the French chemists, Schlosing and Miintz, 

 demonstrated that nitrification is a biological process, 

 thus confirming the opinion expressed some years 

 previously by Alexander Miiller in Germany. Other 

 investigators demonstrated that the putrefaction of 

 nitrogenous materials is brought about by microogan- 

 isms. The ground was thus prepared for a better under- 

 standing of the changes that take place in sewage. 



Intermittent sewage - filtration. — Practical experience 

 with the land treatment of sewage demonstrated that 

 the greater purifying effect, as well as the best plant 

 growth, was secured on rather porous soils properly 



