WATER SUPPLY 259 



the same care should be taken as that outHned above for 

 the construction of a farm well. 



Purifying Water by Filtration. Most people are 

 familiar with the purifying action which water under- 

 goes in its passage through sand, gravel, charcoal, etc. 

 For purifying water used for washing butter, artificial 

 filter beds constructed of such material have given excel- 

 lent satisfaction. 



The filter can described in bulletin No. 71 from the 

 Iowa Experiment Station is 48 inches high, 18 inches 

 in diameter, and constructed of 22 gage galvanized iron. 

 Beginning at the bottom the filtering material was placed 

 in the can in the following order : (1)2 inches of small 

 flint stones; (2) 22 inches of fine sand; (3) 12 inches of 

 fine coke; (4) 9 inches of charcoal; (5) 2 inches of fine 

 stone or coarse gravel. Two perforated plates are placed 

 in the can, one near the bottom upon which the filtering 

 material rests, the other on top of the fine sand. A third 

 and concave plate is placed near the top with a hole in 

 the center, which directs the water to the center of the 

 filter bed. 



This can has a filtering capacity of 16 gallons per 

 hour, and it is claimed that the filter does not need to be 

 cleaned or renewed oftener than once in four months and 

 possibly not this often. The cost of the can is $11.11. 



Filtration offers one of the cheapest methods of purify- 

 ing water and is the method generally employed by cities 

 that are dependent upon lakes for their water supply. 



Purification of Water by Heating. Water may be 

 pasteurized in the same manner as cream. There is, how- 

 ever, one objection to this method of purifying water, 

 and that is the bad effect which it has on the pasteurizer. 



