BACTERIA IN THE INDUSTRIES l8l 



4. Boiling the water for 30 minutes. Very satisfactory for rendering 

 contaminated waters entirely safe for drinking purposes. 



5. Ultra-Violet Rays. — The high voltage ultra-violet ray mercury lamp 

 has been used quite successfully by the French army in the sterilization of 

 drinking water. The lamps are of quartz which permit the more effective 

 passage of the ultra-violet rays, and are placed directly into the water and 

 are said to have a radius of action of one foot and sterilization is said to be 

 complete in one minute without resulting in any physical changes in the 

 water. The rays are not effective in heavily polluted waters nor in water 

 which is not clear. Heavily polluted waters may first be clarified and 

 partially purified by precipitation (the alumn method) and filtration 

 (through sand, charcoal, cotton, etc.). 



6. Centrifugal Purification. — The centrifuge has recently come int 

 extensive use for the purpose of clarifying and purifying liquid substances 

 of various kinds, as gelatinous solutions, plant juices, syrups, oils, paints, 

 varnishes, beers, wines, etc. High speed turbine driven machines are now 

 upon the market making from 24,000 to 40,000 revolutions per minute 

 (the Sharpies Centrifuge). The Sharpies machine is of the continuous 

 feed type which may be operated by hand (25,000 revolutions) or by 

 either steam or compressed air (40,000 revolutions). This machine will 

 render water absolutely clear no matter how heavily polluted, and it is 

 said to remove most of the bacteria. In case of water which is suspected of 

 containing disease germs (typhoid, cholera, etc.) the centrifuging must be 

 followed by chemical or ultra-violet ray sterilization. 



The analyst will find details for the application of the sand-alum 

 filtration and the use of calcium hypochlorite in Field Hygiene by Ford 

 and in Sanitation for Medical Officers by Vedder and in other works on 

 sanitation. 



The analyst should be thoroughly familiar with the subject of water 

 purification and should assist the sanitary officers in their work. Steriliza- 

 tion of drinking water by means of chemicals has been very carefuUy 

 worked out by the armies in Europe. The following chemicals have been 

 used. 



1. Chlorinated lime (chloride of lime) with 35 per cent, available 

 chlorine gas. Action depends upon the hypochlorous acid formed. 

 Amount used ranges from 1-1,000,000 to 1-25,000. A chlorinated lime 

 containing 75 per cent, available gas is on the market and is preferable to 

 the weaker lime. 



2. Sodium hypochlorite is more efficient and also more expensive. 

 Use about the same amount as of chlorinated lime. 



3. Sodium bisulphate in tablets, 30 grains to the quart of water, shake. 



