In a continuation of the geochemical prospecting research program of the U. S. Geological Survey (4), a field method for the rapid estimation of traces of arsenic in soils has been developed. Small anomalies of cobalt in soil have been shown to indicate hidden cobalt ore deposits in the Blackbird area, Idaho (S), where some of the ore consists of cobalt minerals containing arsenic.

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The growing use of geochemical prospecting methods in the search for ore deposits has led to the development of a field method for the determination of cobalt in soils. The determination is based on the fact that cobalt reacts with 2-nitroso-l-naphthol to yield a pink compound that is soluble in carbon tetrachloride.The carbon tetrachloride extract is shaken with dilute cyanide to complex interfering elements and to remove excess reagent.The cobalt content is estimated hy comparing the pink color in the carbon tetrachloride with a standard series prepared from standard solutions.The cobalt 2nitroso-l-naphtholate system in earbon tetrachloride follows Beer's law. As little as 1 p.p.m. can be determined in a 0.1-gram sample. The method is simple and fast and requires only simple equipment. More than 40 samples can be analyzed per man-day with an accuracy within 30% or better, THE U. S. Geological Survey is investigating the amounts of trace elements in rocks, soils, plants, and water as a means of locating hidden ore bodies. To facilitate these studies, methods of quantitative analysis suitable for field use are being developed.