530 



The only chemical tests at this place were made August 2, 191 1, 

 and July 11 and November 15, 1912. August 2, the oxygen ratios 

 opposite Peru varied from 3.17 to 3.51 parts per million (35.8 to 

 39.6 percentages of saturation), according to the place in the river 

 from which the samples were taken. A carbon dioxide test of water 

 taken from near the south side of the stream under the bridge gave 

 6.6 parts per million. 



July II, 1912, the oxygen in the river at Peru was lower than in 

 the preceding August — 2.7 parts per million, equivalent to 32.2 per 

 cent, of saturation at the temperature of the time. November 15, 

 on the other hand, the oxygen ratio was 8.9 parts per million — 71.3 

 per cent, of saturation. As the old Illinois-AIichigan Canal opens 

 into the Illinois River at La Salle, it was a point of interest to 

 know the character of the water which it was adding to the stream 

 at that place. July 11, 1912, the oxygen ratio within the mouth of 

 the canal was 4.31, and November 15 it was 9.7 — the former 51 

 and the latter 75 per cent, of saturation. Local contaminations by 

 sewage, gas wastes, and wastes of the zinc works were disturbing 

 elements at La Salle, the situation being further complicated by the 

 inflow of uncontaminated water through the Vermilion, a short dis- 

 tance above on the opposite side of the Illinois, and the station was 

 consequently dropped in 1912. 



Spring Vallky 



July II, 1912, there was decidedly less oxygen in the water at 

 Spring Valley than at Peru — 1.95 parts per million, as compared 

 with 2.7 parts, the water temperatures being yy^ F. at both points. 



