2l6 



ANALYSIS OF WATER 



should not exceed 20 per cent, of the total solids, but 

 the information obtained from the test is not particu- 

 larly reliable. 



In a good water for general purposes the dissolved matter will 

 not exceed 50 parts per 100,000. Higher values than this indicate 

 excessive hardness (see 222, p. 230). 



Organic Matter. 

 211. The organic matter present in water is generally estimated 

 by measuring the free or saline ammonia, the albuminoid ammonia, 

 and the amount of oxygen absorbed in a given time. From these 

 three figures a general idea may be obtained of the condition, 

 nature, and source of the organic matter, as well as a fair idea of 

 its actual amount. 



Reagents. — For the estimation of the ammonia, free 

 and combined, the following reagents are required. 



{a) Nessler Reagent. — This is a solution in potassium 



hydroxide of a double salt of mercuric and potassium 



- iodides, which gives with ammonia a 



reddish brown precipitate or a coloured 



solution, according to the concentration. 



The depth of colour of the solution is 



proportional to the am.ount of ammonia 



present. The reagent is prepared by 



dissolving 62-5 grams of potassium iodide 



in 250 C.C. of distilled water, and then 



gradually adding (with constant stirring) 



a cold saturated solution of mercuric 



chloride, until a very slight permanent 



precipitate remains. A cold solution of 



150 grams of caustic potash in 150 c.c. 



Fig. 29.— Bottle of water is then mixed with the above, 



for storing Nessler and the total volume made up to I litre 



reagent. ^j^j^ distilled water. The solution is 



allowed to remain in a closed vessel for about three 



days, and the clear liquid then decanted into a bottle 



^ 



