1905.] with reference to the Purification of Sewage. 243 



Filters. — In this procedure the liquor trickles continuously through the filter- 

 bed, being uniformly distributed by sprinklers, while as perfect aeration as 

 possible of the bed is maintained. 



The objects of the present research were mainly the following : — 



1. The detailed chemical study of the course of the nitrification occurring 

 during the filtration of sewage, especially during the maturing period of the 

 filter, and the comparison of the " contact " and "continuous" methods 

 (Section I). 



2. The isolation and study of the organisms concerned, and comparison 

 with those isolated from the soil by Winogradsky. The amount of organic 

 matter accumulated in a sewage filter is comparatively great, and it seemed 

 most unlikely that nitrification should here also be the work of bacteria so 

 extremely sensitive to the presence of organic matter. One seemed com- 

 pelled to believe that other and different bacteria must be here engaged 

 (Section II). 



3. The study of the question of absorption of ammonia upon the surface 

 of filtering material previous to nitrification (Section III). 



These researches were begun in Vienna in 1901, and were resumed in 

 Munich in 190:!, after a break of two years. I am very happy to have this 

 opportunity of thanking Professor Max Gruber for his kind hospitality 

 extended to me in the hygienic institutes of both cities, as w r ell as for the 

 valuable advice and kind assistance he constantly gave me in the course of 

 the work. My thanks are also due to the Royal Commission on Sewage Dis- 

 posal for granting me leave of absence in 1903 to continue the research 

 in Munich. I should also add that part of the expense of the work was 

 defrayed by a grant from the Koyal Society. 



Section I. — Chemical Study of Nitrification in Experimental Filters. 



Description of Apparatus and Methods of Analysis. — Small experimental 

 filters were erected, consisting of glass cylinders 50 cm. high and 12 cm. in 

 diameter ; these were placed one above the other, fitted well together by 

 means of specially ground rims, and covered on the outside with black 

 glazed paper. There were altogether three filters, differing only in height — 

 200 cm., 100 cm., and 50 cm. respectively. Fig. 1 is a diagram of the filter 

 of medium height, showing the arrangements made to allow of samples being 

 drawn off, and of the temperatures being measured at different depths ; the 

 tall filter, consisting of four cylinders, had the three upper ones similarly 

 constructed. The filters were filled with small coke, carefully sifted and of 

 a uniform size (mean diameter 3 - 5 mm.). By volumetric measurements with 



