PURIFICATION OF WATER FOR DRINKING PURPOSES 203 



are generally much less striking. On the other hand, 

 in experimenting with the soluble chemical precipitant 

 lime, we carefully confined our attention to its use in 

 such proportions as are employed in the actual treat- 

 ment of water by Clark's Process, whilst Krtiger has 

 employed larger doses, in which bactericidal effect is 

 superimposed on mere precipitation, with the result 

 that, of course, much greater reductions in the number 

 of micro-organisms were obtained. 



Some further experiments on the subject of sedi- 

 mentation have more recently been made by Messrs. 

 Y. and A. Babes ; J but as their investigations are for 

 the most part a repetition of those already made by 

 other authors, it will not be necessary to deal with 

 them in detail. It has long been known that alum has 

 a remarkable purifying action upon water, and it is em- 

 ployed in various systems for water purification, such 

 as the Hyatt, the American, &c. ; it has also been shown 

 by Leeds 2 to be very efficacious in the removal of bac- 

 teria. This investigator found that by the addition of 

 one half-grain of alum to a gallon ('007 grm. per litre) of 

 water the number of micro-organisms was reduced 

 from 8,100 in 1 c.c. of untreated water to 80. 



In the experiments by Y. and A. Babes much larger 

 quantities of material were used, as will be seen by 

 reference to the following table : 



Bacterial Purification of Water by means of Alum 

 (V. and A. Babes) 



Microbes in 1 c.c. 

 Untreated water contained 1,200 



Powdered alum 



To 1 litre was added 0*25 g. contained after standing 12 hours 



0-2 



0-15 



,, ,, 0-1 ,, ,, ,, a few micro-organisms. 



1 ' Ueber ein Verfahren, keimfreies Wasser zu gewinnen,' by V. and 

 A. Babes, Centralblatt f. BaJcteriologie, vol. xii., p. 132, 1892. 

 - Potable Water, Floyd Davis, Boston, 1891, p. 86. 



