ANALYTICAL EDITION
June, 1944
377
SENSITIVITY
Tests were made to determine the sensitivity of the method to small variations in procedure. It was found that the tartaric acid, bromine water, and dimethylglyoxime added could be decreased 25y0 or increased 100% without affecting the results. The ammonium hydroxide may be decreased 20% or increased 507, without effect. Approximately the same range of values holds for the sodium hydroxide. It was determined that the time elapsed between adding the dimethylglyoxime and the sodium hydroxide i. not ciitical SO long ar it exceedq 1 minuteLe., color development iq complete in less than 1minute. Three identical samples equivalent to a standard steel containing 0.60% nickel were prepared, using for each sample 0.125 gram of National Bureau of Standards Bessemer steel 10d and 0.125 gram of nickel-chromium stee1.32~. To sample 1 the sodium hydroxide, which arrests color development as well as preventing iron precipitation, was added 30 seconds after adding dimethylglyoxime; to sample 2,jminutesafter adding the dimethylglyoxime; and to sample 3, 10 minutes after adding the dimethylglyoxime. In each case the solution was diluted to the volumetric mark and mixed immediately after adding the sodium hydroxide. Transmittance readings in each case were taken 10 minutes after adding the sodium hydroxide. The results, expressed in terms of the analysis of the steel as read from the 0 to l.y0nickel curve, averaged 0.599% nickel with a maximum deviation from the average value of 0.0057, nickel. INTERFERENCES
The method wab tested for interference by copper, cobalt, tungsten, molybdenum, chromium, and vanadium. The small amounts of copper (less than 0.2%) present in the usual steels did not interfere. Copper, when present to the extent of 0.50(7, in the steel, caused a positive nickel error of 0.027,. Cobalt, tvhen added to thr sample equivalent to 2.57, in the steel, caused a positive error of 0.037, nickel. Both elements were tested for interference on a
