86 Bacteria in Relation to Country Life 



The Woolf method.- — Considerable success has attended 

 the use of methods that are distinctly chemical in their 

 action, but involve the employment of electricity. One 

 of these, known as the Woolf method, is based on the 

 decomposition of weak salt solutions by a current 

 from the dynamo, whereby the compound sodium 

 hypochlorite is formed. Sodium hypochlorite has a 

 marked germicidal effect, and the addition of the elec- 

 trolyzed solution to the water causes the destruction of 

 the bacteria in the latter. Because of the quantities of 

 material required to effect the sterilization of water, 

 this method can hardly be regarded as economically 

 practicable. 



Purification by means of ozone. — There is more prac- 

 tical significance in the purification of water by means 

 of ozone. When electrical discharges occur in the air, 

 a portion of its oxygen is converted into ozone. This 

 phenomenon is utilized in the purification of water. 

 Electric sparks are passed through dry air, and after the 

 latter is ozonized it is made to bubble through the water 

 to be purified. The method is reported to be efficient 

 with water containing moderate quantities of organic 

 matter. The bacteria are readily destroyed, tests 

 with Bacillus coli having demonstrated their entire 

 elimination in a number of instances. The organic 

 matter itself is partly oxidized, and the ammonia 

 converted into nitrates. With water rich in organic 

 matter, the ozonization method does not appear to be as 

 satisfactory as could be desired. 



Filters for domestic •purposes. — ^There are various 

 types of small filters for domestic use. It is well known 



