1886.] KETV YORK ACADEMY OF SCIENCES. 47 



maximum daily supply of 200,000,000 gallons, though the time 

 for such an extended provision would be very remote. As a mat- 

 ter of fact, the population supplied by the companies in May of 

 this year was 5,274,542, and the average daily supply during the 

 month was 160,388,316 gallons. Of this more than half, or 

 82,366,466 gallons, came from the Thames, and the balance from 

 the river Lee, and from certain chalk springs in the valleys of 

 the Lee and Thames, and from 21 deep wells sunk into the chalk 

 formation to the north and south of London. There are 44 suh- 

 siding reservoirs for unHUerediuater, with an area of 465 acres, 

 and an available capacity of 1,290,100,000 gallons, and 53 covered 

 reservoirs for storage of tlie water after filtration with a capacity 

 of 160,002,000 gallons." The number of filter beds is 99, with an 

 area of 98 acres. Of this surface, 92 acres were cleansed during 

 the month of May, some of the filter beds being cleansed once 

 and partly gone over again during the month. The maximum 

 permissible rate of filtration is two feet per hour and per square 

 foot of surface, but as a matter of fact the actual rate in the 

 month of May last was generally much smaller than this, some 

 filters passing only 1^ feet. The construction of the filters varies 

 greatly, the top layer, however, being in all cases fine sand, in 

 depth from 2 to ^\ feet. 



From the published analyses it appears that the quality of the 

 water supplied to London is usually satisfactory, though at times 

 results are obtained adverse to that portion of it which is derived 

 from the Thames. The population of the drainage area of the 

 Thames is very large, and although the towns located therein are 

 compelled to purify their sewage, yet much polluting material 

 from them and from the floating population on the river finds 

 its way into the river. 



Though the importance, and in many places the necessity, 

 of purifying our water supplies by artificial methods have been 

 well recognized, yet the great first cost of construction of the 

 English system of filter-beds, the number of laborers required 

 to keep them in efficient action, and their failure to satisfy all 

 the requirements which are essential to an entirely satisfactory 

 system of water purification has prevented their coming into use 

 in this country. There has grown up, by the labors of our own 

 chemists and engineers, a system which is designed to meet our pe- 

 culiar needs, and luhich may he most conveniently and accurately 

 designated as the American system of water purification. 

 It comprises three distinct features: 



1. Artificial aeration under pressure. 



2. Precipitation of dirt, sewage, hardening constituents, and 

 coloring-matters by harmless precipitants: i. e., assisted precipi- 

 tation. 



