132 proceedings of the cotteswold club 

 Artificial versus Natural Purification 



It was stated at the commencement that all water is 

 impure, that rain washes impurities out of the air, and 

 out of the soil. Water which has received contamination 

 in this way can be purified by filtration, and the natural 

 filtration of water is constantly in progress, the water 

 sinks through beds of gravel and sand, chalk or oofitic 

 rock, and issues from their base as springs, or collects 

 into wells that may be sunk through the porous rocks. 

 The water is much purer than was the rain after washing 

 the Earth's surface ; it has lost the greater part of the 

 organic material it contained as well as its bacteria. This 

 natural purification of water can be imitated artificially 

 by passing water through prepared filters. Gravel and 

 sand are generally employed as the filtering media for 

 artificial filtration and the result of passing water through a 

 well prepared filter of this kind is very satisfactory, a large 

 proportion of the organic matter as well as all or nearly all 

 of the bacteria present in the water being removed. In some 

 respects artificial filtration is superior to natural filtration 

 inasmuch as one knows exactly what is being done with 

 the water, and the purification is so to speak in one's own 

 hands, at all events it may be made superior and more 

 efficient than some natural filtration, and it is not necessary 

 for the purification of water to have filters of such vast 

 thickness as is atforded in nature by beds of chalk, oolite, 

 or sand, measuring hundreds of feet. The same practical 

 results can be obtained with not more than 4 or 5 feet of 

 sand and gravel if the filtering process be not hurried. 

 Professor E. Frankland who formerly had little faith in 

 artificial filtration, after making a very careful investigation 

 of the action of sand filters has stated in effect that it is 

 possible to purify water by sand filtration to as great a 

 degree as if it had been obtained from a deep well after 

 passing through hundreds of feet of chalk. Professor 

 Koch, of Berlin, has recently shown that the efficiency of 



