WATER SUPPLY FOR TROOPS 459 



ride of lime or potassium permanganate. They are not used as 

 sources of drinking- water in the presence of sufficient pure 

 supplies. 



In many cases a sanitary survey of the surroundings of the 

 source of water is valuable in locating the contaminating influ- 

 ences. Once located, steps to abate the nuisance may be taken. 



Sanitary analyses and the more complete bacteriological ex- 

 aminations are usually limited to completely equipped labora- 

 tories. The motor field laboratories in use by the British armies 

 and their allies are capable of handling this work. In addition 

 to these, smaller and more portable laboratories have been de- 

 signed. Some of these small laboratory outfits have a very 

 limited field of usefulness. The smaller equipment can, how- 

 ever, be used with small bodies of troops or when the more cum- 

 bersome nature of the motor laboratory would interfere with 

 the hurrying up of additional combatant units. Under the press 

 of such conditions the examinations would in all probability 

 have to be dispensed with and all drinking water presumed to 

 be unsafe. The French had provided more than two hundred 

 portable toxicological laboratories as early as the m.iddle of 1915. 

 These laboratories are particularly charged with determining 

 whether or not wells have been poisoned by mineral poisons, 

 alkaloids, glucosides, cyanides and the like. They are also ex- 

 pected to investigate the character of the gasses used by the 

 enemy and to devise emergency defensive measures. 



The Medical Department in our army is also charged with 

 making such boiler analyses as are require 1 for the military 

 railways operated by the Engineers. 



The U&3 of the unstable hypochlorites of calcium and sodium 

 in purifying water necessitates frequent analysis of the chemical 

 employed in order to be sure tbL,t a sufficient quantity of the 

 active chlorine is applied. Sometimes the water which has been 

 treated by the hypochlorites is tested by means of potassium 

 iodide and starch. In the presence of any free chlorine the 

 familiar blue color of iodide of starch appears. A compound 

 of zinc iodide and starch claimed to be very stable is also issued 

 at times. 



In the absence of data regarding the quality of water supplies 

 as has been mentioned, all the water used is to be considered 

 contaminated. When the quality of several sources is known, the 

 water from the least polluted should be used, even though it is 



