Attack by Oiling i6i 



required depends upon the spread of the oil, the 

 alignment of the stream, roughness of banks, grade, 

 algae present, obstructions, etc. For economic 

 control a trial should be made at each ditch or 

 stream where a drip is used to determine the re- 

 quisite rate of flow. In many cases the drip need 

 only be operated continuously for one or two days 

 a week. On long streams or ditches it was some- 

 times necessary to use several drip cans, so placed 

 that where the effect of the drip at the source of 

 water ceased, the next drip was installed. Settled 

 dry weather may permit the discontinuance of 

 some drips and allow their location to be changed. 

 The isolated pools remaining in the drying stream 

 bed were treated by using knapsack sprayers. 



In practice it was found that drips required 

 periodic attention. Each drip should be visited 

 and adjusted at least twice a week; when new, 

 three or four times a week. Even the best designed 

 drip has required this periodic attention. 



Occasionally it may be necessary to install drips 

 on streams subject to freshets. On such streams 

 they should be secured to prevent their being 

 carried off by a flood. 



Another way to obtain a continuous application 

 of oil is to use cotton waste impregnated with it. 

 This method has a limited field of application, but 



