Field determination of nanogram quantities of mercury in soils and rocks

A method for determining nanogram quantities of mercury in geological materials is based on the catalytic effect of mercury on the reaction of ferrocyanide with nitrosobenzene to produce a violet-covered compound whose intensity if proportional to the mercury present. The mercury is released by heating a sample of soil or crushed rock to about 650°C. As little as 30 nanograms of mercury (30 parts per billion with 1 gram sample) can be detected. The reliability of the method is adequate to permit its use in geochemical surveys that utilize mercury as a pathfinder element.