WATER SUPPLY FOR TROOPS 463 



candle-filter is not considered satisfactory for field use. The 

 British army had a water filter-cart in use at the heginniug of 

 the war. It was a 110 gallon cart provided with, a Pasteur filter 

 preceded by a preliminary sponge filter. It was soon found 

 that the filter candles were so fragile and unreliable that the 

 carts were ordered used for the treatment of the water by 

 chemical disinfection. The German army has experimented 

 very extensively with all sizes of candle filters ranging from a 

 single-candle knapsack filter to multiple-candle filters with a 

 capacity of 2000 liters per hour. 



Where coagulation is employed, a comparatively coarse filter 

 may be used for bacterial removal. Chemical coagulation is 

 dependent upon the production of a gelatinous precipitate in 

 the water to be purified. This precipitate entangles the bacteria 

 and suspended matter, thus gathering them into larger particles 

 which may be more readily removed. Sometimes sedimentation 

 alone is depended upon for the purification of the coagulated 

 water and sometimes filtration is employed. The coagulant 

 usually employed in military practice is alum. 



Of the field filters using coagulation the most important are 

 the Ishiji, Darnall, and drifting sand types. The Ishiji was 

 the filter used by the Japanese in the Russo-Japanese war. The 

 filter was a conical canvas baf with two radial arms or spouts 

 a short distance above the bottom. In each of these arms there 

 was a filter of charcoal and sponge. 



The Darnall filter is the invention of Lieut. C. R. Darnall of 

 the Medical Department. It consists of three nested galvanized . 

 cans in a crate, a siphon of iron pipe and a filter frame which 

 attaches to the siphon. The filter frame carries a specially 

 woven: cotton-flannel filter cloth which is wrapped around the 

 cylindrical metal frame when in use. A coagulant composed 

 of equivalent amounts of potassium alum and sodium carbonate 

 is supplied. In practice the apparatus is assembled and the 

 filter sterilized by siphoning hot water through it. The chemical 

 is then added (rate one pound to 550 gallons) and the siphon is 

 fstarted. The filter can deliver fifty gallons of water with a bac- 

 terial removal of 95 to 98 per cent. It weighs about fifty-two 

 pounds when knocked down for shipment. Although the bac- 

 terial removal is sufficient to render safe a moderately polluted 

 water, the filter should be depended upon only as a means of 



