1896.] MICROSCOPICAL JOURNAL. 89 



Bacteriologic Results From Mechanical Filtration. 



BY GARDNER T. SWAJR.TS, M. D. 

 Secretary of the State Board of Health. 



PROVIDKNCB, R. I. 



At the last meeting of this association* at Montreal 

 the statement was made in the report of the committee 

 on water supplies that no data had been available to show 

 that filtration by the so-called mechanical methods was 

 successful in removing bacteria. The writer at that time 

 referred to experiments which had been made in the city 

 of Providence, R. I. in order to determine this question 

 for the purpose of establishing a plant capable of filtering 

 15,000,000 gallons daily if the experiments were success- 

 ful. 



The figures showing these results were not at that time 

 available, and as they never have been published and as 

 no experiments of a similar character have been made, it 

 seems desirable to place these facts before the Associa- 

 tion, inasmuch as many municipalities are agitated over 

 the advisability of introducing the so-called natural or 

 sand-bed filtration or mechanical filtration. 



The mechanical form of filter used in the experiments 

 was of the type in which quartz or sand is used as a sup- 

 porting bed to a film of precipitated coagulant or fixative 

 of organic matter, produced by the introduction into the 

 water, before filtering, of some chemical such as iron or 

 alum ; a filter which is also cleansed by means of a re- 

 versed current of the water passed through the filter as- 

 sisted by the use of a rake made to revolve in the bed of 

 the quartz while the washing is being done. 



The filters used in this line of experiments were two of 

 the natural sand-bed form imitating the usual filter bed. 



*The American Public Health Association, meeting held in 1895 at 

 Denver, Colo. 



