337-339] Analysis of Water for Drinking Purposes 201 



337. Estimation of Suspended Matter. — This 

 operation is unnecessary unless the water be distinctly turbid. 



Wash a 6-inch disc of filter paper with distilled water free 

 from ammonia. When about 2 litres has passed through, test 

 the last portion for ammonia by Nessler's test (see page 203). 

 If the water has ceased to dissolve ammonia, dry the paper in 

 the air oven at ioo° C. until it is of constant weight. 



Shake up the sample of water, measure out 2 litres, and filter 

 through the prepared paper. Collect the nitrate in a clean 

 bottle (Winchester quart). Next wash thoroughly with distilled 

 water, rejecting the washings, and dry in the air bath, as before, 

 until it ceases to lose weight. The weight of suspended 

 matter in 2 litres of the water is thus found. Calculate this 

 into grains per gallon. 



Next, cutting up the filter, place in a weighed platinum dish, 

 and ignite over an Argand until all carbonaceous matter is 

 driven off. Cool in a desiccator, and weigh. On subtracting 

 the weight of the dish and the filter ash, we obtain the weight 

 of inorganic suspended matter in 2 litres of the water. 



338. Microscopic Examination.— In cases where sus- 

 pended matter is present it is usual to make a microscopic 

 examination. In this case a quantity of the water is left in 

 a tall cylinder, and the undissolved matter allowed to settle. 

 The supernatant water is carefully poured off, and the mud 

 at the bottom placed on a slip of glass and examined by the 

 microscope. For information as to the microscopic appear- 

 ance of sediments, see Hassal's ' Food and its Adulterations.' 



339. Total Solids in Solution.— Should the water have 

 been filtered, this estimation is made in the filtered portion. 



Measure out 500 c.c. of the water in a graduated flask, and 

 fill an accurately tared platinum evaporating basin about half 

 full of water from the flask. The water may be evaporated 

 over a water bath, or, better, over a rose burner protected by 



