a mercury drop arrangement tests electrochemically a sample solution , in a horizontal or vertical orientation , employing mercury which is delivered from a mercury reservoir to the test solution via a valve and mercury capillary tube . the mercury is valved to deliver one drop of mercury to the end of the capillary tube which is immersed in the sample solution . an electrochemical test of the sample solution can be performed when the mercury drop is in place , and if the mercury drop is not in place , the mercury in the capillary tube forms a microelectrode . the mercury capillary tube can easily be removed for replacement or cleaning when the valve is closed . closing of the valve produces electrical isolation of the reservoir contents from the mercury in the mercury capillary tube , including the mercury drop itself . such electrical isolation from the mercury reservoir precludes electrical noise generated in the reservoir from contaminating the voltammetric data . environmental concerns are addressed by the invention in that mercury consumption is reduced , and operator exposure to mercury is eliminated . in addition , the invention facilitates remote control over the mercury electrode , and therefore is particularly adapted for monitoring harsh environments . very small capillaries can be employed in the practice of the invention , and pressurization of the mercury reservoir facilitates initialization of the mercury electrode arrangement , and to prevent entrapment of air .