D3230_10 (13)

The conductivity of solutions is affected by the temperature of the specimen when measurements are made. The temperature of the test specimen at the time of measurement shall be within 3 degrees Celsius of the temperature at which the calibration curves were made. Establish a blank measurement by following the procedure in section 10.3 and 10.4 of the Written Standard, omitting the mixed salt solution. When the indicated electrode current is greater than 0.25 milliamperes at 120 volts AC, water or another conductive impurity is present, and its source must be found and eliminated before calibration can be completed. Determine a blank measurement for each time fresh xylene or mixed solvents is used. Into a dry, 100-milliliter graduated glass-stoppered mixing cylinder, add 15 milliliters of xylene. From a 10-milliliter pipette, total delivery-- see section 6.3 of the Written Standard-- or 10-milliliter graduated cylinder-- see section 6.3.1 of the Written Standard when applicable-- add 10 milliliters of neutral oil. Rinse the 10-milliliter pipette or 10-milliliter graduated cylinder with xylene until free of oil. Make up to 50 milliliters with xylene. Stopper and shake the cylinder vigorously for approximately 60 seconds to effect solution. Add a quantity of dilute mixed salt solution in accordance with table 1 of the Written Standard that is appropriate to the range of salt contents to be measured. Dilute to 100 milliliters with mixed alcohol solvent. Again, shake the cylinder vigorously for approximately 30 seconds to effect solution and allow the solution to stand for approximately 5 minutes. Pour the solution into a dry test beaker. Immediately place the electrodes into the solution in the beaker, making sure that the upper edge of the electrode plates are below the surface of the solution. Adjust the indicated electrode voltage to a series of values-- for example, 25, 50, 125, 200, and 250 volts AC. At each voltage, note the current reading and record the voltage displayed and the current to the nearest 0.01 milliamperes. Remove the electrodes from the solution. Rinse with xylene, followed by naphtha, and allow them to dry. With some apparatus, the detailed settings will not be required since the electrodes are built in for autoranging. Determination of the blank and calibration standard responses are the same. Repeat the procedure in section 10.3 of the Written Standard using other volumes of mixed salt solution, dilute solution, as needed to cover the range of chloride contents of interest. Subtract the value obtained for the blank measurement from the indicated current readings of each standard sample. And plot the chloride content-- ordinate-- against net current milliamperes reading-- abscissa-- for each voltage on a 3-by-3 cycle log-for-log paper or other suitable format.