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Dicke, Robert J. (ed.) / Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume XLIV (1955)

Lawton, Gerald W.
An investigation of the chemical oxygen demand determination,   pp. 45-56 PDF (3.1 MB)

Page 45

Hydraulic and Sanitary Laboratory, Civil Engineering 
Department, University of Wisconsin 
 The biochemical oxygen demand (B.O.D.) determination for evaluating the
strength of domestic and industrial wastes is now used almost universally.
Despite its wide acceptance it possesses the great shortcoming that five
days are required for reliable data. A test that would give results in a
much shorter time would of course be very desirable. Many attempts have been
made to select a chemical oxygen demand (C.O.D.) test that would give the
same results in a matter of hours or minutes. The difficulties encountered
in such ' tests arise from the fact that chemical oxidation of organic matter
follows ' different paths and stops at different points from those of biochemical
oxidation. Thus the values obtained by B.O.D. and C.O.D. determinations may
have a high degree of correlation but ordinarily they are not the same. 
 Moore, Kroner, and Ruchhoft (1) as well as Ingols and Murray (2) have given
brief histories of the many attempts made to develop a satisfactory C.O.D.
test,. The main oxidizing agents that have been used are potassium dichromate,
potassium permanganate, ceric sulfate, and iodic acid. Standard Methods for
the Examination of Water and Sewage (3) at present describes an oxygen consumed
test using potassium permanganate as the oxidizing agent. From recently published
results (1) (2) (4) it appears that a dichromate oxidizing solution is the
most reliable and is not difficult to use. 
 Rhame (4) used potassium dichromate as the oxidizing agent in a mixture
of equal parts of sulfuric and phosphoric acids. He determined the unused
dichromate by means of potassium iodide, starch, and sodium thiosulfate.
His method did not consider the loss of volatile materials by evaporation
from the open container during boiling, and it did not use a constant mixture
that would maintain a constant boiling temperature. These two conditions
undoubtedly produced results that were not readily reproducible. 
 Ingols. and Murray (2) employed the same oxidizing agent that Rhame had
suggested and similarly determined the amount of unused reagent. They refined
Rhame's method by refluxing in 

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