METHODS OF PURIFYING WATER 



61 



Central Scientific Lo. 

 FIG. 93. LAHOUATOKY STILL 



ing water. Have you performed the distillation ex- 

 periment suggested at the beginning of this topic ? 



How are temporary and permanent hardness re- 

 moved from water? Have you ever heard water 



spoken of as "hard" or as 

 "soft" water? Does the wa- 

 ter in your locality quickly 

 and easily form lather with 

 soap or does it lather with 

 great difficulty? 



We have already learned 

 that water is a good sol- 

 vent. As water seeps 

 through sand and rock lay- 

 ers of the earth it dissolves 

 some of the substances 

 with which it comes in con- 

 tact. Thus when this water 

 is used for home or indus- 

 trial purposes it has in it 

 some dissolved solids. Wa- 

 ter containing dissolved 

 substances is called hard 

 water. Water without any 

 dissolved solids in it is 

 called soft water. Rain water is soft water. 



Hard water generally has calcium, magnesium, or 

 iron compounds dissolved in it. If these compounds 

 can be removed by boiling, the water is said to possess 

 temporary hardness. The soluble substances are 

 changed to insoluble substances by heat, and settle 



out. This produces the hard 

 crust often found in tea 

 kettles and boilers. Do you 

 know what boiler scale is? 

 Dissolved solids which 

 cannot be removed from 

 water by boiling produce 

 what is known as perman- 

 ent hardness. Heat has no 

 effect on the dissolved sub- 

 stances in permanently hard 

 waters. Soap can be used 

 to soften water, but it is more economical to use some 

 cheaper substance. Washing soda (sodium carbonate 

 or sal soda) and borax are the chemicals most com- 

 monly used for this purpose. Washing soda is six 

 times more effective in softening water, pound for 

 pound, than soap. Also washing soda is cheaper per 

 unit of weight than soap. 



Courtesy Heine Boiler Co. 

 FIG. 94. BOILER SCALE IN A 

 PIPE 



REFERENCES FOR FURTHER STUDY 

 Texts 



Caldwell and Curtis, Science for Today, Chap. 5 

 Clement, Collister, and Thurston, Our Surroundings, Chap. 5 

 Hunter and Whitman, My Own Science Problems, Unit 4 

 Lake, Harley, and Welton, Exploring the World of Science, 



Chaps. 6, 7 



Pieper and Beauchamp, Everyday Probletns in Science, Unit 5 

 Powers, Neuner, and Bruner, The World around Us, Chaps. 



6,7 



Skilling, Tours through the World of Science, Tour 4 

 Van Buskirk and Smith, The Science of Everyday Life, Chap. 



5 



Watkins and Bedell, General Science for Today, Chap. 4 

 Webb and Beauchamp, Science by Observation and Experi- 

 ment, Units 1, 3, 4 (parts) 



Wood and Carpenter, Our Environment: Its Relation to Us, 

 Unit 1 ; Our Environment: How We Adapt Ourselves to It, 

 Unit 3; Our Environment: How We Use and Control It, 

 Chap. 6 



Special references 



Garnett, A Little Book on Water Supply 

 Hessler, Junior Science 

 Prudden, Drinking Water and Ice Supplies 

 Meister, Water and Air 



WHAT YOU SHOULD AIM TO ACQUIRE FROM 

 THIS STUDY 



1. A knowledge of the impurities commonly found 

 in water. 



2. A knowledge of the common methods in use to 

 purify water. 



3. A knowledge of how to purify water in your own 

 home. 



TEST OF MASTERY OF THE TOPIC 



In your notebook complete the statements, answer the 

 questions, and comply with the instructions. 



1. Water for drinking purposes can be safely purified in 

 the home by . 



2. Soft water is water that does not contain 



3. Three different classes of impurities found in water 

 are . 



4. Temporary hardness can be removed from water by 



5. Three methods commonly employed by cities to purify 

 water are . 



6. The disease most commonly spread by impure water 



7. Define distillation. 



8. Permanent hardness of water may be removed by 



9. Permanent hardness of water is due to 



10. Some chemicals used to purify water are 



11. What is heavy water, where is it found, and how is 

 it obtained? 



