$6 IOWA ACADEMY OF 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 oxj^^en 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. 

 tLetfmann & Beam, Examination of Water, p. 41. 



