464 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



clarification. This is a very important office since chemical 

 sterilization is more satisfactory with a well-clarified water. 



The drifting- sand filter is an adaptation of a devise perfected 

 at Toronto. It has been put in use in the war zone chieflj^ 

 through the efforts of Lt. Col. Xasmith. chief of the mohile 

 laboratories of the Canadian army. The advantage of the appa- 

 ratus is the continual cleaning- and replacing of the soiled sand 

 layer on the surface of the filter. It is larger, heavier and of 

 greater capacity than the Darnall and Ishiji filters and there- 

 fore not so valuable for small bodies of moving troops. 



The more important chemical disinfectants which have been 

 used for field purification of water are the permanganates, the 

 acid sulphates, iodine, bromine and chlorine. The latter is used 

 in the fomi of the hypochlorites of calcium and the alkalies, as a 

 liquid, or as a gas. 



Ozone has also been employed, but it has the disadvantage of 

 requiring considerable heavy apparatus including a gasoline en- 

 gine and dynamo, as well as expert attendance. The same objec- 

 tion applies to the ultra violet ray apparatus which has been pro- 

 posed. 



Potassium permanganate is a slow and uncertain germicide. 

 However, it will produce a brownish precipitate which may be 

 used to advantage as a coagulant. The chief use of the perman- 

 ganates has be^n in India where they have been extensively used 

 in the disinfection of wells at times of cholera epidemics. 



The acid sulphates — usually represented by sodium bisulphate 

 — are dependent on their acid character for their disinfecting 

 •power. They, too, are particularly effective against the cholera 

 organism. As much as one gram per pint is employed. The un- 

 pleasant acid taste is obscured 'by compounding into the tablets 

 lemon oil and saccharin. They are not suitable for continued 

 use on account of the laxative character of the sodium sulphate 

 formed. They were supplied to the New Zealand troops during 

 the Boer war and have been used during the present war by the 

 British cavalry. The acid attacks the metal of the canteen and 

 some canteens may yield toxic metals to the water. Troops who 

 are to use these sodium bisulphate tablets are supplied with 

 aluminum water bottles. 



Iodine and bromine are not usually used for purification be- 

 cause they are more expensive than the chlorine compounds. 

 Their germicidal powers are about the same. Any excess of thfo 



