430 ANALYTICAL CHEMISTRY. 



Total residue left on evaporation : 500 mg. 



Potassium permanganate decomposed by organic matter: 10 mg. 



(=31.71 c.c. ^KMn0 4 ). 



Ammonia, present as such or as an ammonium salt : 0.05 mg. 

 Albuminoid ammonia i. e., ammonia formed from nitrogenous organic 



matter by distillation with KMnO 4 : 0.1 mg. 

 Mtrates : 10 mg. of N 2 O 5 . 



Nitrites : a mere trace, not to exceed Q.05 mg. of N 2 O 3 . 

 Sulphates : 60 to 100 mg. of H 2 S0 4 . 

 Chlorine : 15 mg. 

 Phosphates : a mere trace. 

 The water should be clear, colorless, odorless and practically tasteless. 



Total solids. If the water be turbid, a liter of it is passed through a small 

 filter, previously dried and weighed. After drying at 110 C., filter and con- 

 tents are weighed together and the difference is quantity of suspended solids. 

 The evaporation to dryness of one liter of the clear water in a platinum or 

 nickel dish at a moderate temperature, with subsequent heating to 110 C., 

 gives the total inorganic and organic solids in solution. 



The subsequent heating of the dried residue to redness causes the expul- 

 sion of all organic matter ; but as also inorganic matters, such as carbon dioxide 

 from acid carbonate, oxygen from nitrates, etc., may escape, the determination 

 is of relatively little value. 



Organic matters. While we have no good method by which the quantity 

 of organic matter in water can be readily determined, the oxidizing power of 

 permanganate for organic matters is used for an approximate determination. 

 This is made by acidifying 100 c.c. of water with 5 c.c. of sulphuric acid, and 

 adding 10 c.c. of -~- potassium permanganate, or enough to impart a distinct 



red color. The liquid is boiled for ten minutes. Should the red color disap- 

 pear, more permanganate must be added. When color remains permanent, 

 10 c.c. of ~ oxalic acid are added and the mixture is again heated. To this 



solution permanganate is added until it shows a red tint. From the total 

 number of c.c. of permanganate used, 10 c.c. are deducted for the oxalic acid 

 added. 



As the organic constituents in water at different times and places have no 

 uniform composition, the quantity of organic matter present cannot be calculated 

 from the quantity of permanganate used. It is therefore customary to speak 

 simply of the oxygen- consuming power of water. It should, however, be re- 

 membered that water may contain deoxidizing agents, other than organic 

 matters, such as hydrogen sulphide, nitrites, ferrous salts, etc. 



Ammonia. Nitrogenous organic matters, when undergoing decomposition 

 by the agency of bacteria, generate ammonia, which is gradually converted 

 into nitrites and nitrates. It is for this reason that the presence of these three 

 compounds is looked upon as indicative of nitrogenous matters, though small 

 quantities of ammonia and nitrites may also be present in the water by ab? 

 sorption from the air. 



