94 THE AMERICAN MONTHLY [March 



ing from 92.8 per cent, to 98.8 per cent. As to tlie 

 mooted' dangers attending the use of alum in the applied 

 water and which is held up as a warning by the oppo- 

 nents of mechanical filtration, this much may be said in 

 reference to this series of experiments : 



While it was necessary to add half a grain of sulphate 

 of alumina per gallon of water filtered in order to obtain 

 the most satisfactory results, yet upon comparison by the 

 most careful chemical tests of the water applied to the 

 filter and that of the efiluent, there was found to be less 

 alum in the filtered water than in the river water itself. 



Inquiry from numerous manufacturers using alum as 

 precipitant in various quantities in excess of the amount 

 used in the experiments, revealed in no instance any in- 

 crustation or scaling in the boilers where such filtered 

 water had been used. Communications with various 

 boiler insurance companies elicited no report of scaling 

 where such water was used. There is no recorded in- 

 stance where alum-treated water as a drinking water has 

 produced any ill effects upon the consumers. 



This work was done by order of the City Council of 

 the city of Providence and under the direction of a com- 

 mission consisting of the Superintendent of Health, the 

 City Engineer and the Commissioner of Public Works. 

 The immediate supervision of the operation was under 

 the supervision of Dr. C. V. Chapin, the Superintendent 

 of Health and a member of this Association, while the 

 application of the various tests was made under the direc- 

 tion of Mr. Edmund B. Weston, C. E., from whose com- 

 pilations and reports these abstracts have been taken. 

 Most of the bacteriological work was done by the writer. 



Inasmuch as the writer, as well as every person con- 

 nected with the experiments, commenced the investiga- 

 tion with the firm belief that successful mechanical filtra- 

 tion was not possible from a bacteriologic view, it 



