.462 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



and can deliver purified water at a temperature only about five 

 degrees above that of the raw water. The disadvantages are 

 the necessity for skilled attendance, difficulties with sticking 

 valves and the liming of the kettle and heat exchange surfaces 

 as well as occasional difficulty in securing fuel. The Forbes 

 sterilizer, which is of this type, was adopted by the United 

 States Army in 1898, but has been abandoned on account of the 

 troubles in the field. Wheeled mountings for these sterilizers 

 have been desig-ned in addition to the smaller portable types. 

 Among- the foreign apparatus are the Griffith, Rietschel and 

 Henneberg, and Vaillard-Desmaroux types. 



Filters of all sorts have been desigtied for use in the field. 

 Improvised barrel filters made of two barrels — one within the 

 other and the space between them filled with sand — are men- 

 tioned b}^ most writers on military hygiene. There are also 

 filters of cloth, sponge and charcoal. At the other extreme are 

 the exceedingly fine candle-filters such as the Berkefield, Pas- 

 teur and Chamberland filters which operate under pressure. 



Of course the filter should be constructed according to the 

 service expected of it. The cloth, sponge and coarse sand filters 

 can only be expected to remove the larger animal and vegetable 

 forms of life, 'and the coarser suspended matter. They will not 

 take out the finer suspended matter and bacteria unless thej' 

 are aided by coagulants. In filtering a water containing much 

 suspended matter the candle filters soon clog. They are intended 

 to remove such small objects as the bacteria. 



In the museum of the Equipment Board at Hock Island there 

 are a number of filter-canteens. In these some sort of a candle- 

 filter is set into the neck of the canteen and expected to operate 

 by suction applied by the mouth. If these filters yield water 

 sufficiently rapidly to satisfy the soldier, they cannot be fine 

 enough to retain the bacteria, and if tney yield the water too 

 slowly, the soldier will surreptitiously remove the filter and drink 

 the unfiltered water. 



The oandle-filter has been widely used in military posts and 

 has given good service when properly handled. It is necessary 

 to clean and sterilize the candles frequently, as bacteria begin 

 to grow through them in a few days. The cleaning and sterili- 

 ziation of a hundred or more of these fragile candles is quite 

 bothersome. There is, moreover, continual difficulty in keeping 

 the candle-housings tight under pressure. For these reasons the 



