48 TRANSACTIONS OF THE [NOV. 29,. 



3. Mechanical filtration through filters capable of rapid re- 

 versal of current, and cleansing by mechanical means. 



ARTIFICIAL AERATION. 



One of the easiest and most inexpensive methods of improv- 

 ing the quality of water is by means of artificial aeration. The 

 importance of natural aeration has been recognized from time 

 immemorial, and the effect of tumbling down natural falls and 

 rapids, passing over artificial dams, and of agitation by winds 

 and storms, in l^eeping water lively and sweet, is too well known 

 to need more than passing mention. It is of especial interest to 

 us that this mode of improving water wa.s Jlrst applied to citi/ 

 tvater srqjjjJy in consequence of the extremely offensive taste and 

 odor of the Schuylkill water in January and February, 1883. 

 The fact that the analyses revealed the presence of a large amount 

 of sewage in the Fairmount water did not explain its peculiar 

 offensiveness at that season, for there have been times, before 

 and since, when it contained even more sewage and was not so 

 unpalatable. But it appeared to me very noteworthy that the 

 oxygen which ought to be present in a state of solution was 

 largely deficient. Much of it had been used up in the oxidation 

 of the sewage, and the river, being ice-bound from its source to 

 Fairmount Dam, had no opportunity of taking from the 

 atmosphere sufficient oxygen to replace that which had been lost. 



Eeflecting upon these facts, I thought it worth while to try 

 the effect of submitting the disgusting samples from Fairmount 

 Pool to artificial aeration. I found that they not only took up 

 from the air forced to them the oxygen they lacked, but also 

 that much of the sewage to which their offensiveness was due 

 was destroyed. These experiments suggested to me the idea of 

 pumping air into the lower ends of the mains at the pumping- 

 stations. This way of introducing the air was not only the 

 easiest and simplest, but it also afforded an opportunity of 

 placing the mixture of air and water under a maximum pressure. 

 Air, as is well known, consists of twenty-one parts by volume of 

 oxygen and seventy-nine parts of nitrogen; but the oxygen is 

 more soluble in water than the nitrogen, and therefore the 

 greater the pressure to which a mixture of air and water is sub- 

 jected, the larger is the relative amount of oxygen made to enter 

 into solution. 



The study of the subject received fresh impetus from the con- 

 dition of the water supply of Hoboken in the latter part of July, 

 1884. At that time, the oxygen, in a number of samples from 

 the Hackensack River, whence the supply of Hoboken is derived, 

 fell to 3.87 c.c. per litre, and the total dissolved gases to 

 14.93 c.c. Contemporaneously, the same waters, when im- 



