92 



ILLINOIS ACADEMY OF SCIENCE 



The Levy values do not increase with nitrite but remain 

 about the same as with distilled water — uniformly higher 

 than the Winkler. The Winkler is .36 p.p.m. high with .2 

 p.p.m. N as nitrite, .60 p.p.m. high with .5 p.p.m. in N as 

 nitrite Rideal-Stewart and Hale-Melia values are practically 

 the same and check fairly well with the standard Winkler value 

 on the same water, nitrite-free 



The same procedure was followed with a second batch of 

 samples with the exception that .5 and 1.0 p.p.m. N as nitrite 

 were added. The results are shown in Table II. 



TABLE II. 



.5 p.p.m. 1.0 p.p.m. 



Aerated, N N 



distilled, H,0 as nitrite as nitrite 



Levy 8.35 7.95 7.95 



Winkler 7.58 7.97 8.79 



Rideal-Stewart 7.48 7.56 



Hale-Melia 7.84 7.61 



Levy values are uniformly higher than the Winkler standard 

 on distilled water. The Winkler is .39 p.p.m. high with .5 

 p.p.m. N as nitrite, 1.21 p.p.m. high with 1.0 p.p.m. N as 

 nitrite. Rideal-Stewart and Hale-Melia values are approxi- 

 mately the same as the Winkler value on aerated distilled 

 water. 



In the next series of experiments 5 per cent and 10 per cent 

 of sewage were added. The results are given in Table III. It 

 must be remembered that the addition of fresh sewage to 

 aerated distilled water reduces the dissolved oxygen content 

 due to oxygen consumption by micro organisms, hence these 

 results are comparable only in each dilution. 



TABLE III. 



Aerated, 5 pet. 10 pet. 



distilled, H 2 sewage sewage 



Levy 8.30 8.27 7.73 



Winkler 7.95 7.42 6.78 



Rideal-Stewart 7.32 6.81 



Hale-Melia 7.25 6.65 



In the presence of the organic matter of sewage, the Levy 

 values are still considerably higher than the Winkler or its 

 modifications. The Winkler, Rideal-Stewart and Hale-Melia 

 values are all practically the same. Evidently the organic 

 matter has not destroyed iodine to any extent. 



This point was studied further, as follows: 

 Dissolved oxygen was determined in mixtures of nitrite-free 

 sewage and aerated water; the remaining amount of liquid, 



