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It cannot be denied, as Mr. Feigl and others have shown, that extremely small amounts of both elements and compounds can be determined by chemical spot tests wherein the specificity of certain reagents, acting upon the sample, is manifested by a color reaction. Let us now consider their application to metals and more particularly ferrous alloys. On innumerable occasions, someone will rush up to the chemist with a bar or two of something metallic and hastily ask whether these contain chromium, nickel, titanium, or some other elements. Sometimes he will merely say, “Are these two materials the same tiling?” The one doing the testing can use a choice of methods to satisfy such a person. By using the techniques of Feigl and others, he can systematically go about searching for the individual elements and give a decision. Secondly, he may use a “relative technique” to differentiate the two or more materials. The theme of this paper is based on this so-called “relative technique” for, by it, the spot test procedure can be most easily transplanted from the chemist in the laboratory to the inspection or stockroom man out in the shop for daily use on a production-line scale. Consider, for example, two alloys, A and B, that are used in the same area of production line and subject to mixture by the usual means. Both alloys A and B may be identical in composition except that 2 per cent of the base metal iron in alloy B has been replaced by tungsten. To use a regular spot test for tungsten would involve a considerable amount of time for testing and separating each bar of the mixed stock. On the other hand, if there is a certainty that only alloys A and B are present at the point in question, it would be much easier to add, for example, a drop of concentrated HNO3 which gives a green spot with alloy A and a black spot with alloy B.
Head Analytical Group, General Electric Co., West Lynn, Mass.