88 DOMESTIC WATER SUPPLIES FOR THE FARM 



through the ground precludes any effective filtration or purifica- 

 tion, and the seepage entering the well will carry with it in prac- 

 tically unmodified form any polluting matter it may have picked 

 up at the surface or in the surface soil. As a prevention it was 

 often formerly the practice to surround the outside of the stone 

 curb with a layer of puddled clay, but the more common treat- 

 ment at the present time is to lay the portion of the curb above 

 the water level in cement. 



Cleaning the Well. In the course of time the material enter- 

 ing the well as dust at the top, or washed in through the 

 ground, forms a considerable accumulation of silt in the bot- 

 tom and on the sides. In some wells this deposit is sufficient to 

 hinder, to a certain extent, the entrance of water into the well and 

 to lessen its storage capacity. Some relief is usually afforded by 

 cleaning out the well. 



In deep dug wells, especially those that have been kept tightly 

 covered, dangerous gases sometimes collect, and lives are not in- 

 frequently lost by descending such wells too soon after they have 

 been opened. Carbon dioxide, one of the commonest of the gases 

 found in wells, may be detected by lowering a lighted lantern to 

 the bottom of the well, the flame being extinguished if the gas is 

 present in dangerous quantities. 



