]]'ArER 561 



In this tank slaked lime is placed and the whole well mixed. 

 The lime throws down the soap as insoluble calcium stearates. 

 It also brings down all the dirt and impurities. 



The effluent flows through a series of three up-and-dcwn settling 

 tanks connected together, the scum is stopped b}' canvas screens 

 placed vertically reaching two-thirds of the distance down from the 

 top and up from the bottom alternately. 



All the calcium stearates settle in the first tAvo tanks. 



The third tank is used for precipitating the lime and removing the 

 soapy oils. Washing soda is run into this tank which produces 

 insoluble calcium carbonates which sink to the bottom. Consequently 

 the soapy oils separate out, float and are collected on canvas. 



The canvas is chang'ed daily. 



The water then flows into a charcoal filter, six feet square by 

 eighteen inches deep with four inches of charcoal between two layers 

 of sacking in a perforated zinc tank. 



It passes from this into a concreted well. 



The water is pumped from this well into an elevated tank for 

 repeated use. 



The mixing tank is cleaned out daily and the sludge is buried. 



The first precipitating tank is cleaned out every third dav. 



The water thus treated is free from dirt, soap, lime, soapy oils and 

 readily lathers with soap. 



4,000 gallons pass through daily and 2,000 men use the same water 

 daily. 



Oxidation. 



The "fishy" waters of Mauritius were made potable bv means 

 of a special oxidation process. The water was run over perforated 

 trays, allowing it to drop 4 to 6 feet, finely divided, during which 

 time the water became almost saturated with oxygen. 



Oxidation is also carried out to some extent during intermittent 

 filtration. The process can be used to get rid of iron. 



This process : — 



(i) Oxidizes the ferrous compounds. 



(2) Oxidizes the ferric hydroxide, in both instances precipitating 



organic matters. 



(3) Facilitates the destruction of residual organic matter. 



(4) Aerates and hence makes potable certain drinking waters. 

 All water should be passed through a filter afterwards. 

 Boiled and distilled water could be aerated in this way. 



Filterable Viruses. 



This term is applied to micro-organisms so small that they will 

 pass through an ordinary fiker which will keep back ordinary 

 bacteria. 



