l82 PHARMACEUTICAL BACTERIOLOGY 



and let stand for 20 minutes. Excellent for small quantities, asi for cavalry 

 men, and for men on the march. 



4. Potassium permanganate, i grain to the quart, or ^enough to pro- 

 duce a pinkish coloration. Particularly efficacious against Bacillus 

 ckolercB. 



5. Calcium permanganate is used in Germany to purify water in the 

 canteens (i grain to the quart). The precipitate which forms must be 

 filtered through plug of cotton or a filter paper cap. 



6. Iodine liberated from the mixing of iodide and iodate, in the canteen, 

 has been used by the French army. The salts are put up in red, white, and 

 blue tablets, ready for immediate use. 



7. Halazone (p-sulphon dichloramino benzoic acid). 1-300,000 is 

 very efficient against typhoid and cholera contaminations. This is cheap 

 and effective. It comes in tablets ready for use. 



The following titrating method for determining the amount of 

 chlorine required to sterilize water supplies is used in the army, as 

 reported by Vedder (Sanitation for Medical Officers, Lea and Febigerj 



1917)- 



1. Into a rinsed ordnance cup (i pint or about 500 cc. capacity) break 

 one tube of calcium hypochlorite and mix thoroughly with a few drops of 

 water. Fill the cup with water to within one inch of the top (500 cc.) 

 and mix well by pouring back and forth by means of a second cup. This 

 solution contains 0.3 gram of available chlorin. 



2. Rinse four ordnance cups with the water to be sterilized and fill 

 all four cups with water to be tested. To first cup add 0.2 cc. of the 

 test solution in cup mentioned in (i). To second cup add 0.4 cc, to 

 third o. 6 cc. and to the fourth cup 0.8 cc. Mix well by pouring back and 

 forth. Let stand for thirty minutes. 



3. Into a clean cup crumble a tablet of potassium iodide (or use a few 

 crystals of the iodide salt), add a little starch solution (made by boiling 

 a little corn starch). Pour into this cup the water to which was added 

 0.8 cc. of the chlorite. If blue color appears, it is an indication that not all 

 of the chlorine has been used up in that mixture. 



4. The cup which contains the smallest amount of the chlorite which 

 will give a blue color, contains the percentage of chlorine required to 

 sterilize the water to be used. 



5. Example. — ^Let us suppose that the cup to which was added the 0.4 

 cc. hypochlorite solution represents the smallest amount just producing a 

 blue coloration, hence enough to sterilize one pint. To sterilize 36 gal- 

 lons (288 pints, the amount in one Lyster water bag) would require 115 

 cc. of the test solution in cup (i). The pint of hypochlorite prepared 

 would therefore suffice to st^rihze a httle over four bags of water. In 



