PUMPS WHICH COMPRESS AIR 20 1 



be at least 75 feet from the well, and in large hotels, where 

 there is necessarily a large quantity of sewage, the distance 

 should be much greater. As the sewage seeps through the 

 ground it loses its impurities, but the quantity of earth re- 

 quired to purify it depends upon its abundance ; a small 

 depth of soil cannot take care of an indefinite amount of 

 sewage. Hence, the greater the number of people in a 

 hotel, or the more abundant the sewage, the greater should 

 be the distance between well and sewer. 



By far the best way to avoid contamination is to see to it that 

 the sewage discharges into the ground beloiv the well ; that 

 is, to dig the well in such a location that the sewage drainage 

 will be away from the well. 



In cities and towns and large summer communities, the 

 sewage of individual buildings drains into common tanks 

 erected at public expense ; the contents of these are dis- 

 charged in turn into harbors and streams, or are otherwise 

 disposed of at great expense, although they contain valuable 

 substances. It has been estimated that the drainage or sewage 

 of England alone would be worth $ 80,000,000 a year if used 

 as fertilizer. 



A few cities, such as Columbus and Cleveland, Ohio, realize 

 the need of utilizing this source of wealth, and by chemical 

 means deodorize their sewage and change it into substances 

 useful for agricultural and industrial purposes. There is still 

 a great deal to be learned on this subject, and it is possible 

 that chemically treated sewage may be made a source of 

 income to a community rather than an expense. 



189. Pumps which Compress Air. The pumps considered 

 in the preceding Sections have their widest application in 

 agricultural districts, where by means of them water is raised 

 to the surface of the earth or is pumped into elevated tanks. 

 From a commercial and industrial standpoint a most im- 



