driving rod 



•stondptpe 



water surface 



streom bed ■ 



Figure 2. 



-Method of placing standpipe in streambed for collection of water samples for determination of 

 dissolved oxygen content. 



from dropper bottles through this tube. Before 

 the sample is agitated, the column of liquid 

 is forced to the top of the tube by applying 

 pressure to the stopper and is sealed from the 

 atmosphere by closing the opening of the 

 tube with the forefinger. 



Analyzing Water Samples 



The unmodified Winkler Method was used to 

 analyze water samples for their dissolved 

 oxygen content. The volume of water used 

 for an oxygen determination was only 30 

 nnl., and it was necessary to employ semi- 

 -nicromethods of analysis to obtain precise 

 readings. A 25-ml. aliquant was ti- 



trated against 0.0125 N sodium thiosulfate 

 solution delivered from a microburette having 

 0.02-ml. subdivisions. The 0.0125 N sodium 

 thiosulfate solution was prepared from a 

 stock solution which was periodically stand- 

 ardized against 0.025 Npotassium dichromate. 



Dissolved oxygen analyses were made in 

 the field near sampling areas. There was 

 very little delay from the time samples were 

 collected to the time they were titrated; 

 thus the possible influence of interfering 

 substances was minimized. 



The collection and analysis of water sann- 

 ples from 200 standpipes required about 1 day 



