46 



The Water of the Mississippi river — Dodge. 



eminent authorifeies on the subject hold that when the foul mtiiters 

 have been introduced into the water of a river, though a part of 

 them is oxidized and destroyed during the onward flow of the 

 stream, yet the process of self-purification is never so complete as 

 to render the dietetic use of the water free from risk. 



In starting upon the analysis of a number of samples of water 

 from properly chosen points along the stream, T had an expecta- 

 tion of finding the above mentioned proposition confirmed more 

 or less decidedly. To proceed at once to a statement of my results, 

 I will present the accompanying table. 



In order that the comparison of a series of water analyses 

 should be perfectly jast, it is of course necessary that they be made 

 throughout under the same conditions. In collecting the samples 

 from the river, they should be taken simultaneously. It was im- 

 possible to conform strictly to this condition; but the samples 

 whose analyses are presented were taken during a period of two 

 weeks at the latter part of February and the early part of March. 

 Those from Hastings and Winona were kindly procured for me by 

 Professor C. W. Hall. In all other respects the samples of water 

 were examined under the same conditions. 



It seemed to me, considering the purpose in view, — namely the 

 purpose of ascertaining if the results of my analyses would support 

 the proposition that the river purifies itself as it flows onward, that 

 the stretch of river between St. Paul and Hastings offered a favor- 

 able example. For, between St. Paul and Hastings there are no 

 considerable streams flowing into the Mississippi and thereby com- 



