836 PARKS 



valve is closed. Calcium hypochlorite is added at the rate of five-tenths 

 to one part per million of free chlorine, or from one to two ounces of the 

 calcium hypochlorite per five thousand gallons ofwater. The amount to 

 be used depends upon the turbidity of the water and can be determined by 

 testing for free chlorine in the treated water. If the water is clear, a solu- 

 tion of calcium hypochlorite (2 ounces dissolved in 3 or 4 gallons of water) 

 is added to the water while it is flowing into the reservoir. If turbid, the 

 water should be allowed to stand for some time, six hours or more, before 

 the calcium hypochlorite solution is added, so that some of the solids will 

 settle out. In any event, the chlorine should remain in contact with the 

 water for at least thirty minutes before it is delivered to the consumer. 



Liquid chlorine may be used where there is regularity of flow and 

 large quantities of water are used. The chlorine gas is liquefied by pressure 

 in steel cylinders, and assumes the gaseous form when released. A solution 

 of the gas is made and applied to the water by means of an apparatus 

 known as a chlorinator (Plate 311). This system should be installed under 

 the direct supervision of an engineer. 



All chlorinated water should be tested daily to determine the amount 

 of free chlorine in the supply as delivered to the consumer, regardless of 

 whether the Lyster Bag method is used or the water purified in reservoirs. 

 Two methods of practical value are available the starch-iodine and the 

 orthotolidin tests. Either of these can be made by an intelligent employee, 

 and it should be the specific duty of some one individual to make tests 

 daily. The water as delivered should contain between o.i to 0.5 part per 

 million of free chlorine. 



The starch-iodine test. Thirty minutes or more after the chlorine has 

 been added to the water a cupful is tested for free chlorine by adding from 

 a medicine dropper ten drops of a solution containing 10 per cent of potas- 

 sium iodide, I per cent of soluble starch, and 0.5 per cent of zinc sulphate. 

 If a blue color appears free chlorine is present and the water is potable. 

 If no blue color is seen the water is still polluted and requires further 

 chlorination. 



The orthotolidin test. As in the starch-iodine test, the water is tested 

 thirty minutes or more after chlorination. A four-ounce bottle is filled to 

 the shoulder with the water to be tested and to this water is then added 

 fifteen drops of an orthotolidin solution consisting of o.i gram of orthotolidin 

 crystals dissolved in 100 c.c. of a 10 per cent hydrochloric acid solution. 

 If a yellow color develops free chlorine is present and the water is potable. 

 If no yellow color is seen more calcium hypochlorite is needed. The amount 

 of chlorine used should be just enough to produce the blue color with the 

 starch-iodine test, or a yellow color with the orthotolidin test. 



