556 TROPICAL HYGIENE, SANITATION, ETC. 



To those accompanying expeditions, &c., the following facts by 

 Dr. Thresh may be useful : — 



(i) Obtain a supply of high quality chlorinated lime in quarter- 

 pound hermetically sealed tins. (From the United Alkali Co. 

 Liverpool.) 



(2) Obtain a corresponding number of half-pound tins of sodium 



hyposulphite. This salt, known more commonly as hypo- 

 sulphite of soda used in photography, is nearly tasteless and 

 combines with all the available chlorine in about half its 

 weight of chlorinated lime. From these the following stock 

 can be prepared. 



(3) Add the contents of a tin of No. i to a gallon of water and 



shake until uniformly mixed. 



(4) Add one packet of thiosulphite to one gallon of water and 



shake until dissolved. 



One gallon of solution No. 3 will sterilize 8,000 gallons of anv 

 ordinary clear well or river water in iifteen minutes, and if at the 

 expiration of that time the one gallon of thiosulphite solution No. 4 

 be added to the water any excess of chlorine will be eliminated. One 

 fluid ounce of No. 3 is sufficient for 50 gallons of water. In no case 

 should less than i part of chlorine be added to 1,000,000 parts of 

 water, and if the water is known to be foul, 2, 3, or even more parts 

 should be used. 



This process can be depended upon to remove any typhoid or 

 cholera organisms which may be present in the water, and the same 

 applies to the species of bacilli which are the probable cause of 

 dysentery. 



Iron is removed by adding lime and then filtering through sand. 



For Anderson's process iron is required. The water passes 

 through revolving drums and is subjected to showers of metallic iron. 

 The excess of the latter is removed by oxidation, precipitation and 

 filtration. It is not applicable to peaty waters. 



Ozone is now becoming better known. The water falls from a 

 tower through rough stones and ozone, which latter is admitted at the 

 bottom of the tower. The ozone rises, meets the descending water, 

 and sterilizes it as it descends. The ozone is prepared by passing 

 dried air through ozonizers supplied with electricity. 



These machines are expensive, but the method is very efficacious. 



Each ozonizer of one horse power and of S,ooo volts A'ields \x$ ^<'' 

 27 grams of ozone in twenty-four hours and sterilizes 26,400 to 52,800 

 gallons per diem. The excess of ozone is lost by passing the water 

 over cascades at the bottom of the tower. 



Water containing iron would still require filtering. 



