Mercury and its salts rank among the most widely used drugs in medicine. The therapeutic value of mercury is well established, but certain of the pharmacologic and biochemical aspects of the compounds of this metal have not been thoroughly studied, owing to the difficulty of determining mercury in the presence of organic matter or halogens. Lomholt and Christiansen1 reported a test which they claimed to be accurate and satisfactory, but it is time-consuming and requires a microbalance. Booth, Schreiber and Zwick2 reported a test which is accurate, but which has certain limitations mentioned by the authors, such as: it is time-consuming, is inaccurate in the presence of iodides and requires special equipment and technic not common to a clinical laboratory. Young and Taylor3 recently described a method for mercury determination which is less laborious, is accurate and does not require special technic. By the use of this