m IOWA ACADEMY OE SCIENCES. 
permanganate solution effected by the presence of a cer- 
tain amount of sodium chloride in the water with which 
it is desired to make the determination of oxygen con- 
sumed. 
The next considertion given was that of selecting the 
methods which are in general use for the determination of 
the oxygen consumed. As a result of an investigation of 
the literature on the subject it may be said that the four 
following methods are those which are most generally 
used : 
I. Kubel Method. * 100 c.c. of the solution is taken 
and placed in a flask; 5 c.c. of sulphuric acid (dilute 1.3) 
is added with a quantity of standard potassium permanga- 
nate solution. The contents of the flask are boiled for five 
minutes; then 10 c.c. of standard oxalic acid solution is 
added and the solution titrated to color with standard 
permanganate. 
II. Schulze Method. 100 c.c. of the sample is taken 
and placed in a flask to which there is added 1-2 c.c. of 
sodium hydrate (one part of sodium hydrate to two parts 
of water) and a quantity of standard potassium perman- 
ganate which will insure a permanent color to the solu- 
tion. The contents of the flask are boiled for ten minutes, 
allowed to cool to a temperature of 50-60°, and 5 c.c. of 
dilute sulphuric acid is added; 10 c.c. of standard oxalic 
acid is then placed in the flask and the contents titrated 
with standard potassium permanganate. 
The permanganate solution used in both the Kubel and 
Schulze methods is a 1-100 normal. 
III. The Association Method f as recommended by the 
chemical section of the American Association for the 
advancement of science. 
To 200 c.c. of the water to be examined in a 400 c.c. flask, 
add 10 c.c. of dilute sulphuric acid (1.3) and such measured 
quantity of the permanganate as will give a persistent 
color; boil ten minutes; add, if necessary, more perman- 
ganate in measured quantities so as to maintain the red 
* Konig, Landwirstschafttiche und gewerblichewichtiger Stoffer. 2nd auf. p.607. 
fLeffmann & Beam, Examination of Water, p. 41. 
