A rapid and accurate method has been needed for the deterruination of copper in steels, ferroalloys, and related raw materials and products. Although many methods have been proposed for the colorimetric determination of copper in such materials, most of them require a number of preliminary separations. The method proposed by Hague, Brown, and Bright (3) for the determination of copper in steels by use of sodium diethvldithiocarbamate gives good results in most cases, but the use of neo-cuproine would eliminate the addition of complexing agents to mask interfering ions, and the extraction procedure would be simplified. The possible interference of iron because of faulty extraction technique would be eliminated. Breckenridge, Lewis, and Quick (1) found, in 1939, that 2,2'-biquinoline was specific for copper. This reagent has been recommended for use in water analysis (2), but it has not been commercially available until recently. Early in 1952, Smith and McCurdy (5) reported that 2,9-dimethyl-l, 10-phenanthroline (neo-cuproine) reacts similarly with copper and that the colored system formed in isoamyl alcohol is slightly more sensitive than the 2,2'-biquinoline system. Other reagents-such as, 2,9-dimethvl-4,7-diphenyl-l,10-phenanthroline-have been suggested, but were not commercially available at the time of this work.This study was made to acquire specific information regarding the copper(I) neo-cuproine system with respect to the accuracy and precision of the system and to determine the effect of certain diverse ions, such as cyanide, fluoride, and sulfide. Early in the
