Colorimetric Analysis

This historic book may have numerous typos, missing text or index. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. 1921. Not illustrated. Excerpt: ... CHAPTER EIGHT. ALUMINUM AND CHROMIUM. 0f the members of the third group of metals, iron was worthy of a chapter by itself, leaving us the remaining two for discussion here. Aluminum, besides its occurrence in rocks and minerals, is determined in cements and plasters. Chromium occurs in minerals to some extent but the big field of usefulness of this test for chromium is the analysis of chromesteel for the chromium content. Aluminum By Alizarin-s. The sodium salt of alizarin monosulfonic acid is a commercial indicator which shows purple with alkalies and yellow with acids. The coloration produced in acid solution1 may be adapted to the determination of aluminum, the test being delicate enough for the detection of one part of aluminum in ten million parts of water. Small amounts of chromium and iron do not interfere, in the presence of large amounts of these metals it is necessary to add citric acid or a citrate to prevent them from showing. It is not advisable to render the solution alkaline with ammonia for the precipitation of the hydroxides from other substances present, as the reagents used are almost certain to contain traces of aluminum. The presence of phosphates or of moderate amounts of calcium, magnesium or zinc salts has no effect on the results. If cobalt is present the solution must never become alkaline. The sample should be chosen to contain between .00005 gram and .000005 gram of A1203. i J. Soc. Chem. Ind., 34, 936. The sample taken is to be dissolved in ten to twenty c.c. as dilute acid as possible or, if the sample taken exceeds the above limits, in a larger amount and an aliquot part taken. If the acid is very concentrated it should be partially neutralized so as to leave the final solution acid' but not too strongly so. If the solution is made...