IOWA ACADEMY OF SCIENCES. 87 



€olor; remove the flask from the lamp, add 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. 



IV. 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 2o0 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 tlie 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. i88i, p. 136; also Leffmann & Beam, Examination of Water, p. 39. 



