IOWA ACADEMY OF SCIENCES. 
87 
color; remove the flask from the lamp, acid lOc.c. of oxalic 
acid solution to destroy the color, or more if required by 
the excess of permanganate, and then add permanganate, 
drop by drop, till a faint pink tint appears. From the 
total quantity of permanganate used deduct the equivalent 
of the oxalic acid used, and from the remainder calculate 
the milligrams of oxygen consumed by the oxidizable 
organic matter in the water. 
IY. The English Method.* This method is the one 
generally used in England by the Society of Public 
Analysts. 
“Two determinations are made, the amount of oxygen absorbed during 
fifteen minutes and that absorbed during four hours; both are to be made 
at a temperature of 80°F. It is most convenient to make these determina 
tions in l2oz. stoppered bottles, which have been rinsed with sulphuric acid 
then with water. Put 250 c.c. or 3,500 grains in each bottle, which must be 
stoppered and immersed in a water bath or air bath until the temperature 
rises to 80°F. Now add to each bottle 10 c c. or 100 grains of the dilute 
sulphuric acid, and then 10 c.c. or 100 grains of the standard potassium per- 
manganate solution. Fifteen minutes after the addition of the permanga- 
nate, one of the bottles must be removed from the bath and two or three 
drops of the solution of potassium iodide added to remove the pink color. 
After thorough admixture, run from a burette the standard solution of 
sodium hyposulphite until the blue color is just discharged. If the titra- 
tion has been properly conducted, the addition of one drop of the solution 
of potassium permanganate will restore the blue color. At the end of four 
hours remove the other bottle, add potassium iodide, and titrate with sodium 
hyposulphite as just described. Should the pink color of the water in the 
bottle diminish rapidly during the four hours, further measured quantities 
of the standard solution of potassium permanganate must be added from 
time to time so as to keep it markedly pink.” 
It will be noticed that the method of the Association is 
very similar to the Kubel method and only differs from it 
in using double the quantity of water and reagents in the 
determination, and boiling for ten minutes. 
It would naturally be expected that the results from an 
investigation of these methods, that the action of the 
chlorine as chlorides would be very little if any in the 
Schulze and English methods, for in the first there is an 
alkaline condition present and in the second the temper- 
ature is so low that it is only slightly above ordinary 
temperature. 
* Analyst. 1881, p. 136; also Leffmann & Beam, Examination of Water, p. 39. 
