58-00] EXPERIMENTS ON WATER 23 



ably with the flame from a rose burner. The water will boil, 

 and the steam will pass over until it comes into the cool flask, 

 where it will condense. In this manner pure water will be 

 collected in the flask, whilst the impurities are left behind 

 in the retort. 



58. For the tests described in the next seven experiments 

 three kinds of water should be used, i.e. distilled water, 

 ordinary water as supplied to the laboratory, and some 

 sample of really impure water, such as drainage water. 



59. Solid Matter in Water.— Half fill three evapo- 

 rating-basins with the different waters under consideration 

 and evaporate each to dryness. Notice the residue, if any, 

 left in each case. When the residue is quite dry hold the 

 dish in a Bunsen flame for a minute or so. Should there 

 be any organic impurities in the water, such as are derived 

 from decomposing animal or vegetable matter, the residue 

 in the dish will become discoloured and blackened. The 

 distilled water will be found to leave no residue. The 

 laboratory water will leave a residue which will probably 

 remain white on further heating. The drainage water will 

 leave a residue which blackens on heating. 



60. Various Dissolved Salts in different Classes 

 of Water. — The common dissolved impurities are the sul- 

 phates and carbonates of lime and magnesia, and in smaller 

 amounts common salt and ammonia. A few experiments 

 are described below to show the method of testing for these 

 impurities, and of roughly comparing the amounts present. 



a. Lime in Water. — Half fill three clean test-tubes 

 with the three samples of water. Place them side by side 

 in the test-tube rack and add to each a few drops of am- 

 monia and a little ammonium oxalate solution ; allow to 

 stand a few minutes. The distilled water will suffer no 

 change, whilst the other two will become cloudy. Notice 

 which gives the thickest cloud, as that one will contain 

 most lime, and will probably be the hardest water. 



