In many areas of the Pacific Northwest, heavy run oft from rain, melting snow, and ice fields causes extreme dilution of the heavy metal content of natural waters.

Actual field work has shown that in many areas it is only practical to apply geochemical methods in the search for copper and zinc if it is feasible to detect as little as 0.001 p.p.m. of these metals in natural waters.

A modification of the dithizone methods which have already been described has been developed. This modified method is simple, as accurate as is necessary for field work, and can readily detect heavy metals in concentrations as low as 0.001 p.p.m. Under favourable conditions, even lower concentrations can be detected by an experienced field man.

During the 1950 field season, we have started to refer to this modification in the use of dithizone as the “emulsion” technique, in contrast to the “classical” dithizone methods employed by earlier writers.

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