JVATER 555 



ingredients as suspended matter, ammoniacal nitrogen and also hard- 

 ness are removed. 



By storage the bacteria become entangled in the precipitate and 

 are carried down. 



(2) Precipitation. 



To assist in this process various substances are added such as : — 



Vegetable Juices containing tannin, e.g., tea, kino, &c., which 

 coagulate the organic matter. Cold tea is therefore an excellent drink 

 for travellers because : — 



It ensures the water having been boiled. 



The tea strains suspended matters. 



The tannin coagulates and precipitates organic matter. 



Chemicals are also used, as alum 6 grains (o"4 grm.) per gallon 

 (4"5 litres) followed by 5 grains (0*3 grm.) of precipitated lime per 

 gallon. Alum also decreases the number of micro-organisms present 

 but not those of the typhoid and cholera groups. 



Chemicals. 



Chemicals are used for softening and purifying water, but all such 

 meithods should be followed by filtering. 



The alum, lime and soda compound method of Maignen's process 

 (anti-calcaire) is well known. All similar processes contain lime 

 which combines with the carbon dioxide and forms a deposit of 

 calcium carbonate carrying down with it the organic matter. 



Clarke's process for softening water is popular. Use freshly 

 burned lime, 6 pounds (2"5 k.) per 100,000 gallons of water, for 

 each degree of hardness. 



The Porter-Clarke process is a modification of this. The former 

 slow process is hastened by filtration under pressure through cloth. 



Chloride of lime is also used, i to 6 parts of available chloride per 

 million is sufficient. Filtration and passing the water through carbon 

 will remove the excess of chlorine. 



If the water is free from suspended matter, calcium hypochlorite 

 is useful. 



Use three parts per million = one part of available chlorine, and 

 remove the excess a little later with sodium bisulphate (Thresh). 

 This more or less sterilizes such water at a cost of id. per 25,000 

 gallons. The onlv apparatus required is that of ordinary tanks. 



Six hundred American cities now use this process. 



In smaller quantities of water use a teacupful of calcium hypo- 

 chlorite and three teacupfuls of water. Of this mixture use one 

 teaspoonful to two gallons (nine litres) of water. Allow it to rest for 

 fifteen minutes. 



