PURIFICATION OF WATER 153 



distillation. Usually a chemical can be added which will form 

 an insoluble compound with the chemical which the water con- 

 tains. This produces a precipitate which can be removed by 

 filtration, or by sedimentation. 



Bacteria and sewage may be removed by passing air into 

 the water and by the effects of sunlight. Nature effects this 

 result in waterfalls and rapids. Water frozen just at the 

 freezing point is comparatively pure. Boiling will kill the 

 bacteria, but will not remove the poisons which the bacteria 

 have produced. 



There may be substances in water which have a lower 

 boiling point than water. If so, they must be distilled off 

 first, and thus removed before the water itself is distilled. 

 Finally, there may be poisons in the water which cannot be 

 removed by any feasible means. See Section 196, Water 

 Analysis. 

 References : 



1. 1501 : 137. Purification of Water. 



2. 1702 : 64-65. Methods of Improving Drinking Water. 



3. 1703 : 45-47. Purification of Water. 



a. 1701 : 50-54. Purification of Water. 



b. 1704 : 28-33. Purification of Water. 



c. 1706 : 39-40. Purification of Water. 



d. 1707 : 69. Purification of Water. 



e. 1708 : 268-270. Purification of Water. 



/. 1709 : 302-323. Purification of Water by Chemical Means. 



g. 1711 : 2-3. Preparation of Pure Water. 



h. 1801:281-282. Distillation, 



i. 1804:287-288. Distillation. 



j. 1808:234-235. Distillation. 



Experiment 57. Precipitation and Filtration. 

 Apparatus : Ring stand, burner, asbestos mat, evaporating 

 dish, test tubes 6" X j", funnel, filter paper. 



