97 

 1891.] ** 4 [Bache. 



drink. That this has heretofore not been attempted is all the 

 more remarkable, because it is believed by many persons that 

 some of the worst forms of pathogenic germs reach us through 

 the medium of drinking water. Inasmuch, therefore, as success 

 in sterilizing the drinking water of a large city might be of un- 

 told benefit to it, it would be well that certain experiments were 

 tried to that intent, upon the assumption that, be the pathogenic 

 germs in a particular water many or few, they become, when re- 

 ceived into the alimentary canal, whether or not large numbers 

 of them are successfully dealt with by the stomach, injurious to 

 the human economy. 



Inherent in the Anderson iron process for the purification of 

 water is a danger which, therefore, cannot be eliminated. In all 

 processes there is a danger line which human foresight seeks to 

 avoid by a safety-margin, which, in the long run, and in the na- 

 ture of things, is a substantial guarantee against harm. But 

 there are processes such, from their character, combined with the 

 chapter of exigencies and the chapter of accidents, that they 

 have but a small margin of safety. I place the Anderson process 

 in this category, as an experience at Berlin, showing the danger 

 that may result from the overworking and freezing, or both, of 

 open filter beds, even if so acted upon and cleansed as they are 

 intended to be by the Anderson process, fully warrants me in 

 doing. Moreover, it should be incidentally mentioned that the 

 process is not applicable to the constitution of all waters, or 

 adapted to climates that have always, or are liable to, severe 

 winter cold. It is said, however, upon excellent authority, 

 based upon the indisputable evidence of microscopic examina- 

 tion, that by the process micro-organisms have, under the limit- 

 ing conditions hereby implied, been neutralized in the proportion 

 of 50,000 to about 20, virtually in the proportion of 50,000 to 0. 

 But, coincidently with this result, which must obtain under 

 favoring circumstances, there also always exists danger in the 

 process through carelessness and neglect in filter cleansing, and 

 necessity without law of overworking the capacity of a filter. 

 As a finality in the process the ferric hydrate generated, blended 

 with organic matter, is precipitated in a flaky, coagulated condi- 

 tion to the bottom of the water, the sand filter-bed of the settling 

 reservoir, where, resting chiefly on the surface, the filter is there- 

 fore more readily than usual cleansed. The process therefore 



