548 



data, consequently, for the interesting section of the river above 

 Marseilles. As this trip extended to the mouth of the Illinois, it 

 can be used from Chillicothe downward as an extension of the 

 midsummer trips of the preceding year, which stopped at that point, 

 to give us an idea of midsunmier conditions for the whole stream. 

 It is mainly interesting as showing an irregular but gradual rise in 

 oxygen ratios from Chillicothe to the Mississippi, from 2 parts per 

 million at the former place to 4.7 at Twelve-mile island, thirteen miles 

 above the junction of the Illinois with the Mississippi. A cross- 

 section of the latter river at Grafton, below the junction, gave 4.85 

 parts per million on the Illinois shore below the mouth of the Illi- 

 nois River, of 7.15 at the middle of the Mississippi, and of 7.65 on 

 the Missouri side beyond the reach of Illinois River water. Other- 

 wise stated, while the oxygen of the water of the Illinois near its 

 mouth lacked in July 39.5 per cent, of saturation, that of the un- 

 diluted Mississippi lacked only 1.5 per cent. The residual effect of 

 the contamination of the former stream was thus a final loss of 38 

 per cent, of its oxygen. 



August to October, ipi2. — Our chemist made in August, Septem- 

 ber, and October, 191 2, only short visits to the river to determine 

 the oxygen ratios where biological collections were in progress, and 

 his data are consequently in fragmentary series only. Four tests 

 made August 21 and 22 at Marseilles, Ottawa, and Starv^ed Rock 

 are of interest for comparison wath those made at Marseilles and 

 Starved Rock August 24 to 26, 191 1, as shown by the following 

 table. 



Marseilles (above dam) 

 " (below dam) 



Ottawa 

 Starved Rock 



1911 191: 



.44 



2.26 



3.43 



1.90 

 2.90 

 3.65 

 4.05 



The mean of the water temperatures for the 1911 period was 

 70.5° F., and that for August, 191 2, was 6° lower; and the river 

 levels at Morris stood some six feet higher in August, 1912, than in 

 August, 1911. These differences of conditions are fairly reflected 

 in the virtual doubling up of the oxygen ratios in 19 12 at the con- 

 trasted points. 



November, IQ12. — For November, 19 12, we have two trips, a 

 fortnight apart, made the entire distance from Lockport to the 



