DELAWAKK RTVKR WATER. 1 39 



are several eddies between Easton and the Delaware Water 

 Gap. In these eddies the current is slack enough to allow 

 the bacteria to settle, and hence the water becomes partially 

 purified. This is one of the good features of the river. 



The effect of sunlight, one of the best germicides known, 

 on water, is also slight. Kxperiments have shown that bac- 

 teria of typhoid and other diseases are killed in a few minutes 

 if exposed to direct sunlight. The energy of the sun's rays 

 in penetrating the water is, however, so quickly absorbed that 

 at a few feet below the surface it loses its power as a germi- 

 cide and hence its effect in deep water is almost 7iil . 



As regards aeration and oxidation, these are very valuable 

 methods, but the effect on the bacterial content is slight. 

 Oxygen is added to the water and it is improved in taste, but 

 the bacteria are not destroyed to any appreciable extent. 



It has been proved that algae are antagonistic to bacteria. 

 Because of their gelatinous character, they sweep through the 

 water and entangle many bacteria and destroy them. We 

 know there are algae in the river during the summer months, 

 and thev undoubtedly rid the stream of many bacteria. 



(2) The second of the factors to be considered is the 

 longevity of pathogenic bacteria. This plays a ver}- import- 

 ant part in judging of water supplies. From the observations 

 of the current in the Delaware it was found that an average 

 approximate velocity of the river was 3.7 miles per hour. 

 The distance from Belvidere by scaling from the map along 

 the river is found to be nearly fourteen miles. This would 

 give the time of flow from Belvidere to be nearly four hours, 

 and from ihe Delaware Water Oap to be about eight and a 

 half hours. It is probably less than this, due to rapids in the 

 upper regions of the river. Now typhoid bacilli have been 

 known to live in water for several months, at the maximum, 

 and several days at the minimum. Thus we see that if 

 typhoid bacteria were deposited into the Delaware River at 

 eifher Delaware Water Gap or at Belvidere, N. J., they 

 would still be very much alive by the time they would reach 



