94 ILLINOIS ACADEMY OF SCIENCE 



The general conclusions to be derived from this work are : 



1. Levy values are higher than Winkler in practically all 

 cases, except where high nitrites are present. 



2. Winkler values are much too high in the presence of 

 high nitrites. Either the Hale-Melia or the Rideal-Stewart 

 modification will give correct results up to 1.0 p.p.m. N as ni- 

 trite and 10 per cent sewage. The procedure of the Hale- 

 Melia is so much simpler than that of the Rideal-Stewart that 

 it is much preferable for field work. 



It is of interest to note that in a large number of comparative 

 determinations of dissolved oxygen on the Illinois State Water 

 Survey 1 were, on the average, 1.0 parts per million higher 

 than results by the Winkler method used by the Sanitary Dis- 

 trict of Chicago. 



The Levy method was used by the New York Metropolitan 

 Sewerage Commission 2 in its work on New York Harbor. 

 The Winkler method was used by Birge and Juday" in their 

 extensive work on Wisconsin lakes. Phelps* has used the 

 Rideal-Stewart method in his work on the Ohio River. Led- 

 erer 5 uses the Hale-Melia method at the Chicago Sanitary 

 District; it is also used by Hale and Melia' at the Mt. Pros- 

 pect Laboratory, Brooklyn, N. Y. Thus it is seen that a stan- 

 dard method is desirable in order that all results may be com- 

 parable. To this end the experiments indicate the advisability 

 of discarding the Levy method, and of officially adopting the 

 Winkler method, with the Hale-Melia modification in the 

 presence of high nitrites. 



The experimental work reported in this paper was done in 

 the laboratories of the Illinois State Water Survey in July, 

 1914. 



1. Unpublished work, 111. St. Water Survey. 



2. Report, N. Y. Met. Sewerage Comm., 1914. 



3. Wisconsin Survey Bull. XXII, page 11. 



4. Jour. Ind. and Eng. Chem., Aug. 1914, pp. 682. 



5. Jour. Ind. and Eng. Chem., Nov. 1914, pp. 884. 



6. Jour. Ind. and Eng. Chem., Dec. 1913, pp. 976. 



