The Water of the Mississippi river — Dodge. 45 



[Paper D.^ 



Written for the rtgiilar meeting of April yd, 1S83. 



Mr. Chairman and Members of the Academy: 



By way of contributing something in the nature of a report 

 of the section of Chemistry at the present meeting, as appointed 

 for that section, I have thought it proper to present some results 

 of recent analyses of the water of the Mississippi river from dif- 

 ferent points in this State. It should be premised however, that 

 the winter or early spring season cannot be regarded as a very 

 satisfactory time for making analyses of the water of the river, 

 with a view to comparison of the purity, or impurity, of the water 

 at different points. The river has been closed over, for the most 

 part, by a thick covering of ice, excluding to a considerable extent 

 the action of the air: while the frozen and snow-covered condition 

 of the banks has prevented the inflow of surface drainage and thus 

 greatly diminished the amount of contamination derived from 

 these sources. Actual sewers have continued to send down their 

 impurities into the river during the cold weather, very much as at 

 other seasons. 



The plan of the investigation Avas to secure samples of water 

 from a number of points along the course of the river, and subr 

 mit these waters to analysis. The results of the analyses were 

 thought likely to have an interest as bearing on the question of 

 the self purification of river waters by processes in the regular 

 course of nature. It is now a commonly known and generally ac- 

 cepted proposition that flowing water, — and water otherwise mov- 

 ing — purifies itself from organic matters of a foul or objectionable 

 nature, chiefly through the action of the oxygen of the air, the 

 movement of the water being regarded as promoting this action by 

 increasing the admixture of the air w^th the water and thus giving 

 greater opportunity for the contact of the oxygen with the or- 

 ganic matters. This I have mentioned as a generally accepted 

 proposition. And it rests upon abundant proof. The only points 

 of difference in connection with the subject are in regard to the 

 extent or completeness of the process of self-purification. It has 

 appeared from occasional paragraphs and communications which 

 I have noticed in the daily papers, that people express quite com- 

 monly a belief in the complete^ or almost complete, removal of the 

 foul matters in question, and that within a very limited distance 

 from the point of influx of these matters. On the other hand, 



