384 



FISHERY BULLETIN OF THE FISH AND WILDLIFE' SERVICE 



Titrations 



Titnitioiis wi-iv dunt' \vi(li ;i IJerkiiiaii /^H lueti-r. 

 The water-sample bottles were calibrated with the 

 solid stoppers on so that the exact amount of 

 water in each sample was known without further 

 measurenT^nt. The titrations were performed in 

 the samjjle bottles to avoid any opportunity for 

 the modification of the gaseous content of the 

 water due to exposure to air in ponring. 



Hydrogen-ion Concentration 



Measm'ements of hydrogen-ion concentrations 

 were made to within 0.0.1 pH unit with a Beckman 

 ;>H meter. A Hellige pocket color comparator 

 was used for rapid pH measurements (to within 

 0.1 ^■^H unit) during adjtistment of valves while 

 setting up experimental conditions and during a 

 number of the earlier exploratory experiments. 



Alkalinity and HCO^. 



In the range of ;?H in which the experiments 

 were made (/>H 7 to pH 6) the alkalinity was 

 assumed to ('(jual tlie concentration of HCO;,. 

 Methyl-orange alkalinity was measured (Ameri- 

 can Public Healtli Association 1946) by titrating 

 tlie sani])le with PLSO^ to an end point of /)H 4.4. 



Carbon Dioxide 



The free, or uncombined, CO, content of the 

 water was measured in two ways. Some of the 

 measurements were made directly by titration of 

 the sample with NaOH (American Public Health 

 Association 1946) to an end point of pU 8.2. 

 Other deteiininations of free CO2 were made indi- 

 rectly bj' measuring alkalinity (methyl orange) 

 and pH and then determining CO2 by the graphic 

 method of INIoore ( 1939 ) . The measurements were 

 made to Avithin 0.1 p. p. m. CO2. Those measure- 

 ments made directly by titrating with NaOH were 

 slightly lower than the measurements made in- 

 directly by the graphic method. Therefore, in 

 comparing the water of the two channels only 

 one method was used for each pair of measure- 

 ments. The range of conditions under which the 

 measurements were made is indicated by figure 8 

 which shows CO- measurements made during the 

 experimentgl 



During the series of tests which examined the 

 orientative influence of CO,, water was modified 

 bj' the introduction of gaseous CO.. Addition of 

 gaseous COj to the almost unbuffered water of 



FREE 



COz (PPM) 



7.0 



SO 



5.0 



4.0 



60 62 6.4 66 6JB 



.H 



Figure 8. — Free CO2 measurements. May 1950. Only 

 measurements of samples of unmodified stream water 

 and water modified by the addition of gaseous CO2 are 

 included. The samples were taken under a wide variety 

 of stream and weather conditions. 



the stream produced several effects. It increased 

 tlte concentration of free CO2 and it decreased the 

 /;H. It also raised the partial pressure, or tension, 

 of CO, in the water. Examples of data from 

 individual tests (table 4) illustrate the first two 

 of these effects. It will be noted that the concen- 

 tration of HCO;j was largely unaffected. In the 

 range of pH in which the experiments were made 

 (pH 7 to ^H 6), carbonates were not present. 



Water was modified by addition of KJ1(P04) 

 during the tests of the orientative influence 

 of pH. Examples of data from individual tests 

 are given in table 4. In these tests the changes 

 in pH were of approximately the same magnitude 

 as the changes in /*H in the tests in which CO, was 

 added (although K.,H(P04) raised the pH. while 

 CO, lowered it). The addition of K,H(P04), 

 however, had much less effect upon the concentra- 

 tion of free CO2. 



During this investigation, measurements of CO, 

 were restricted to the convenient and widely ac- 

 cepted methods available for measuring the 

 amount of free CO,. The importance of measur- 

 ing dissolved gases in terras of partial pressures 



