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7.1-5 <br /> soJ44-. The mixture should be agitated for 24 hours and <br /> maintained at 20°-400C (68° 104 °F) during this time . It <br /> is recommended that the operator monitor and adjust the <br /> pH during the course of the extraction with a device <br /> such as the Type 45-A pH Controller manufactured by <br /> Chemtrix, Inc . , Hillsboro , Oregon 97123 or its equivalent , <br /> in conjunction with a metering pump and reservoir of 0.5N <br /> acetic acid . If such a system is not available, the <br /> following manual procedure shall be employed: <br /> a . A pH meter should be calibrated in accordance <br /> with the manufacturer' s specifications . <br /> b . The pH of the solution should be checked and , <br /> if necessary, 0.5N acetic acid should be <br /> manually added to the extractor until the <br /> pH reaches 5 .0 + 0 .2 . The pH of the solution <br /> should be adjusted at 15 , 30) and 60 minute <br /> intervals , moving to the next longer interval <br /> if the pH does not have to be adjusted more <br /> than 0 . 5 pH units . <br /> C . The adjustment procedure should be continued <br /> for at least 6 hours . <br /> d . If at the end of the 24-hour extraction period, <br /> the pH of the solution is not below 5 .2 and <br /> the maximum amount of acid (4 ml per gram of <br /> solids) has not been added , the pH should be <br /> adjusted to 5 .0 + 0 .2 and the extraction <br /> continued for an additional four hours , during <br /> which the pH should be adjusted at one hour <br /> intervals . <br /> 6 . At the end of the 24 hour extraction period, deionized <br /> water should be added to the extractor in an amount <br /> determined by the following equation: <br />