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Test a portion of the last washing with a dilute solution of ammonium sulphide to assure complete removal of the zinc. The precipitate may then be ignited and weighed as ferric oxide, as described on page 110. PROCEDURE. Acidify the filtrate from the iron determination with dilute nitric acid. Concentrate it to 150 cc. It is important that this point should not be overstepped.
Filter off the carbonate and wash it with hot water, testing the slightly acidified washings for sulphate and preserving any precipitates which appear in these tests. Acidify the filtrate with hydrochloric acid until just acid, bring to boiling, and slowly add hot barium chloride solution, as in the preceding determination. Add also any tests from the washings in which precipitates have appeared.
Acidify the solution with dilute hydrochloric acid, and heat it nearly to boiling. Measure out about 5 cc. in excess of this amount, and pour it into the acid solution. Allow the whole to cool. Decant the clear liquid through a filter, and transfer the precipitate to the filter, using as wash-water a mixture of one volume of concentrated ammonia and three volumes of water.
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