ABSORPTION OF OXYGEN 221 



genous organic substances yield ammonia when treated with 

 alkaline potassium permanganate. It assumes, of course, that the 

 nitrogenous organic matter in water is uniform in character, and 

 that it conforms to the general rule that "the disintegrating animal 

 refuse may be measured by ten times the albuminoid ammonia 

 which it yields." 



In a good drinking water neither free nor albuminoid ammonia 

 should exceed o-oo8 part per 100,000. 



214. Oxygen Absorbed^ or ^^ Moist Combustion!^ 



The organic matter in water is determined, in terms 

 of the oxygen required to oxidise it, by treatment with 

 potassium permanganate. In contact with oxidisable 

 organic matter in acid solution, permanganate readily 

 gives up its oxygen as follows : — 



2KMn04+3H2S04 = K2S04+2MnS04+3H20 + 50. 



The oxidation is not instantaneous, and varies in extent 

 with the temperature. 



By means of this method it is possible to distinguish 

 between readily oxidisable first decomposition products 

 and more complex organic bodies, the former being 

 much more rapidly attacked by permanganate at ordinary 

 temperatures than the latter. The solutions required 

 for the estimation are the following : — 



1. Standard Potassium Permanganate containing 



0-396 gram KMnO^ per litre. 



One c.c. of this solution contains o-oooi gram 

 of available oxygen. 



2. Dilute Sulphuric Acid. — Strength i to 3. 



3. Sodium Thiosulphate solution containing i gram 



NagSsOg per litre. 



4. Potassimn Iodide solution, 10 per cent strength. 



5. Starch solution. 



