88 



tliere has beeu in the different seasons of the year considerable variation iu 

 the quantities of organic matters contained, but it is to be noted that the 

 quantities of oig-anic matters in the water of the Illinois river and iu the 

 lakes adjacent thereto are ordinarily ver^ high even for surface waters. 

 Duriujj: tiie last twelve months the average in the river and also in the lakes 

 shows that the quantity of sewage contained has been considerably less than 

 it was during the preceding twelve months, due of course to the fact that 

 there have been repeated periods of high water and a more generally dis- 

 tributed rainfall during the year of '97-"98 than was the case during '96-'y7. 



Attempts have also been made during the last year to determine the quan- 

 tity of dissolved oxygen and of dissolved or free carbonic acid gas in the 

 waters of the Illinois river and the lakes at Havana. We have met with 

 considerable difficulty in making these determinations because of the necessity 

 of doing most of the work here at Champaign. The conditions ai-e pai-ticu- 

 larly unfavorable for work at a distance because of the large quantities of 

 organic matters contained in the water, and, further, because these matters 

 are in a state of putrefactive change, that is, are undergoing somewhat rapid 

 decomposition. The determinations of dissolved oxygen, consequently, 

 commonly give us figures somewhat too low. Tests made on the spot at the 

 time of collection show that the quantity of dissolved oxygen is ordinarily 

 diminished very quickly on standing a few hours, particularly when the 

 vessels containing the water are exposed to the light. Our results, however, 

 have been obtained under practically similar conditions throughout the season 

 and they show considerable variation, at times the quantity of dissolved 

 oxygen being exceedingly low, while at other times the quantity reached the 

 approximate maximum figure. This is true not only of water contained in the 

 river, but also of the water of the lakes. The data which we have in hand 

 has not yet been digested and can not be until the work has beeu carried on 

 somewhat more extensively. The free carbonic acid, — that is the carbonic 

 acid which exists not in combination with the bases in the water, but 

 as gas merelj- dissolved in the water — varies yet more greatly than does 

 the dissolved oxygen. At times there seems to be none present; at 

 other times the quantity present is quite considerable; but these deter- 

 minations are even more greatlj' influenced by permitting the samples to 

 stand, or by the time which elapses during their transportation to the labora- 

 tory, and we can not at present attach very great importance to the results 

 which have hitherto been obtained. 



We expect soon to be able to extract gases from water by means of an air 

 pump, and then we shall be in a position to obtain results which will not be 

 influenced by the conditions mentioned above, and, provided we shall be 

 able to have collections carefullj' made at Havana, the work can very easilj' 

 be continued and completed here at the University. 



Since early iu the summer of 1897 we have made regular determinations of 

 dissolved oxygen and of carbon dioxide in samples taken from the Illinois 

 river and from Thompson and Quiver lakes, but the earlier results are less 

 reliable than those obtained during the last six months, and these later re- 

 sults are themselves not sufiicieutly reliable to be made at present the basis 

 of any general conclusions. 



Yours very respectfully, 



Arthur W. Palmer, 



Professor of Chemistry. 



REPORT OF THE ENTOMOLOtJICAL ASSISTANT. 



To the Director of the Laboratory. 



Sir: — During the season of 1897 I was iu the field, primarily for entomolo- 

 gical observation and collection, from June 29 to August 13, giving attention 

 particularly to the gathering of information and material for use in complet- 

 ing our work on Odonata and MoJhtsca. In 1898 two visits to the field were 

 madt' for work on Odonata, Ephemerida and Mollusca; a week in spring, from 

 April 19 to 25. and two weeks in midsummer, from June 21 to July 7. 



