Mode of Procedure.
The crucibles were heated, tared, and weighed exactly as in the preceding method. The oxalate was weighed in ground-stoppered weighing tubes from which it was transferred to the inner of the two porcelain crucibles. The pair of crucibles, ([1 and 2 fig. 3]) was placed in a third porcelain crucible and the whole system introduced into an upright air-bath. The outer crucible was supported on a porcelain triangle about an inch from the bottom of the bath and was not allowed to touch its walls at any point. The top of the bath was covered with a sheet of iron over which was placed an asbestos board. The exterior was also covered with a lining of asbestos. A thermometer was introduced well into the bath. The temperature was allowed to rise slowly until the oxalate began to show a brown color around the edge. From this stage the temperature was kept as low as possible in order to effect the decomposition. When the oxalate was decomposed the bath was allowed to cool and the contents of the crucible completely dissolved in nitric acid. The nitrate was evaporated to dryness and decomposed as in the method first described. The end of the decomposition was determined in the same manner and the oxide, free from all impurities, weighed.