Water 



61 



letter S, in the drain pipe just after it leaves the sink. As long as 

 the trap contains water, foul gases will not back up into the house, 

 as sewer gas will not pass through water. 



Distillation of Water. Distillation is a process of purify- 

 ing water by boiling it and collecting the steam which is after- 

 wards condensed back to water 

 by cooling. By this means, all 

 undesirable solid matter in the 

 water is left behind. Gaseous 

 impurities, however, often pass 

 off with the steam. 



To distill water : Fill a flask 

 about one-half full of water and 

 insert in the opening of the 

 flask a rubber stopper. Through 

 this pass one arm of a bent glass 

 tube. The other arm of the tube 

 should reach into a test tube set 

 in a beaker of ice or snow. Heat 

 the water until it boils. As it 



DISTILLING WATER 



boils, the vapor arising from it passes from the flask into the test 

 tube where it is at once condensed into water by coming in contact 

 with the cold surface of the test tube. All solids which were dis- 

 solved in the water will be left in the flask. The distilled water 

 in the test tube will be clear, odorless and tasteless. 



Ice Manufacture. The demands for ice for preserving food 

 in homes and storage plants, for cooling drinks and for making 

 ice cream have enormously increased in recent years. Ice is re- 

 quired in all seasons, and often at points far from the sources of 

 supply the frozen lakes and streams of the north. 



The uncertainty of this supply, the cost of harvesting and 

 shipping, the tremendous loss through melting, and the dangers 

 of impurities in natural surface ice have led to the development 

 of great plants to manufacture artificial ice from pure water. 

 Such plants are now the main source of the ice dealers' supply. 



Manufactured, or artificial, ice is made in ice plants by the 

 evaporation of ammonia or sulphur dioxide gas which has been 



