The difficulties enco untered in using existing colorimetric m ethods for t h e determination of small amounts of aluminum in nonferrous materials are d iscussed . A method is proposed for obviating these difficulties. If the m ethod is combined with a preliminary electrolysis in a m ercury cathode cell, from 0.02 t o 0.08 mg of alum inum can be determined quickly and accurately, without a colorimet er. The lise of the m ercury cathode cell and the effect of interfering substances are also discussed .
In the analysis of copper-base alloys, chiefly brasses fI.nd bronze, difficulties have been encountered in consistently obtaining quantitative depositions of copper in nitric acid solutions, unless the nitric acid solution of copper is either fumed with sulfuric acid or evaporated to dryness and baked moderately. As a result of experiments made to remedy this trouble, it has been found that complet e deposition of copper is obtained if a trace of chloride ion (1 drop of 0.1 N hydrochloric acid) is added to the nitric acid solution either during the solution of the alloy or at the beginning of the electrolysis.
A gravimetric method is described for the' determination of tin in copper-base and lead-base alloys. The procedure involves separation of the tin by distillation, precipitation with cupferron, and ignition to stannic oxide. Results obtained by applying the method to known amounts of tin and to a number of nonferrous alloys show that an accuracy to ± 0.2 mg can be expected for amounts of t in ranging from 0.05 to 0.24 g.
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