2o6 SEWAGE AND ITS PURIFICATION 



as the total average amount of suspended matter present in the 

 tank at any instant when M is the weight of suspended organic 

 matter present in the volume of sewage dealt with per day. 

 The size of the tank required is, therefore, not so large as to be 

 impossible with ordinary sewages, but the fact that the effluent 

 from such a tank was not sufficiently purified without further 

 nitrification prevented the *' Automatic Scavenger " from being 

 more generally adopted. 



About 1880 E. S. Philbrick, of Boston, Mass., constructed in 

 a number of places in America sewage plants comprising " a 

 tank or tight cesspool in which the solid particles of the sewage 

 may become macerated and finely divided by fermentation 

 before entering the distribution pipes." ^ It was noticed that 

 the scum and deposit increased rapidly at first, and then 

 practically remained constant. In one case after four years 

 it was found that the surface accumulation was very small 

 (about I foot), and the bottom deposit less, showing that septic 

 action was going on, though it was then imperfectly known. 

 These tanks had the submerged inlet and outlet ; they were 

 circular, but in other respects were very similar to the Exeter 

 septic tank. Glover in 1882 took out patents in America for 

 liquefying tanks followed by aerating filters.^ 



At the time of the Royal Commission of 1882, owing to the 

 failure of most sewage farms to yield satisfactory results, pre- 

 cipitation and attempted disinfection or sterilization, as de- 

 scribed in the preceding chapters, were elaborately carried out. 

 In January, 1887, Mr. Dibdin observed at the Institution of 

 Civil Engineers that. 



*' One object claimed for the use of an excessive quantity of lime, 

 and also for some other substances, is that they destroy the living 

 organized bodies, such as bacteria, etc., which give rise to the 

 phenomena known as putrefaction. . . . As the very essence of 

 sewage purification is the ultimate destruction, or resolution into 

 other combinations, of the undesirable matters, it is evident that an 

 antiseptic process is the very reverse of the object to be aimed at. . . . 

 Very alkaline effluents, such as those produced by the use of lime in 

 excessive quantities are very liable to putrefy instead of becoming 

 purified by oxidizing organisms." 



Meanwhile, bacteriology had been advanced by a large 

 number of researches in various countries, at first directed 



^ Engineering Record, New York, May 10, 1883, p. 530. 



2 For further details see Metcalf's "Antecedents of the Septic Tank," Trans- 

 actions of the American Society of Civil Engineers, xlvi., No. 909, 1901. 



