187 



and bottom waters, but determinations of these dissolved gases 

 made by Professor Palmer immediately upon collection in the 

 field, yielded results which throw some doubt upon the value of 

 those made on samples which were shipped for analysis at the 

 laboratory of the Chemical Survey. Twenty-four to forty-eight 

 hours elapsed between the time of collection and that of anal- 

 ysis, and during this time changes no doubt took place in the 

 gases dissolved in the samples, so that the results of the analy- 

 ses give no trustworthy basis for a statement of the amount 

 of dissolved oxygen and carbon dioxid in the water at the time 

 of collection. 



I am indebted to Professor Palmer not only for the data of 

 the chemical analyses which he has furnished me from the 

 records of the Chemical Survey, but also for many other cour- 

 tesies in connection with this subject. 



COMPARISON OF CHEMICAL CONDITIONS AND PLANKTON AT THE DIF- 

 FERENT STATIONS. 



In Tables X.-XIII. will be found data from the chemical 

 analyses of the waters of Illinois and Spoon rivers and Quiver 

 and Thompson's lakes, together with plankton data of the same 

 or contiguous dates. The most important of the determinations, 

 those of chlorine, oxygen consumed, free and albuminoid am- 

 monia, organic nitrogen, nitrates and nitrites, as well as the 

 plankton, are graphically shown in Plates XLIII.-L. 



CHEMICAL ANALYSES OF WATER FROM PLANKTON STATIONS. 



PARTS PER MILLION. 



AVERAGES OF ALL ANALYSES. 



* Plankton and silt averages are for collections coincident with or contig-uous to collections of 

 water samples. 



The foregoing table gives the number of samples analyzed 

 from each locality and the averages of the different substances 



