The rapid estimation of mercury in the atmosphere of workrooms.

To measure the hazard to the worker it is often necessary to determine the atmosphere concentration of mercury in a workroom. It should be borne in mind that inhalation of mercury, though probably the most dangerous, is not the only way by which mercury enters the body. It follows that a measurement of the mercury content of the atmosphere does not give a full indication of the hazard. Air analyses are useful in determining the degree to which the workers are exposed; this is especially true of those not handling mercury, but working in the same atmosphere as those who do. Such analyses are also a means of keeping a check on the general good housekeeping of the workroom. In the method described by Stock and Heller (1926) mercury vapour is removed from the atmosphere by trapping in chlorine water, while in the method described later by Stock and Cucuel (1934) mercury vapour is, removed by passing the air through a tube cooled in liquid air. The mercury is then dissolved in chlorine water and deposited electrolytically on a copper wire. Fraser (1934) collected mercury from the air using solid carbon dioxide and ether or liquid nitrogen as his cooling agent. Mercury vapour may also be collected in alkaline hypobromite (Buckell, Hunter, Milton, and Perry, 1946; Milton and Duffield, 1947), in a solution of iodine in potassium iodide (Barnes, 1946), or in a mixture of potassium permanganate and sulphuric acid (Kuziatina, 1939). Dusts of mercury compounds have been collected in nitric acid in an impinger or a Palmer dust machine (Jacobs, 1941), or on a filter paper followed by digestion of the filter paper (Milton and Duffield, 1947; Buckell and others, 1946). An examination of some of these techniques revealed certain practical drawbacks. The methods of Stock and Heller, Stock and Cucuel, and Fraser all require electrolytic separation and are therefore too time-consuming for field use. The method described by Barnes proved insufficiently sensitive. Hypobromite solution as a trapping agent as described by Milton and Duffield, and by Buckell and others has proved less efficient than the acid permanganate of Kuziatina. The method described below is the outcome of the experimental work and field experience gained over the last six years. Its advantages are that it is quick and easily carried out under field conditions with standard laboratory apparatus. It uses the acid permanganate scrubbing solution of Kuziatina but determines the trapped mercury by extractive titration with standardized dithizone in chloroform instead of allowing the sample solution to stand with the reagent. Using an extractive titration, interference from copper is minimized. Barnes (1947) has shown that the speed of extraction of copper by dithizone in chloroform increases with increase ofpH but is always much slower than that of mercury. At apH of less than 2 copper is extracted only on prolonged shaking. Using carbon tetrachloride the speed of extraction of copper is of the same order of that of mercury. The method is sensitive to mercurial dusts as well as to mercury vapour, and so for most purposes it is an improvement on the electronic mercury vapour detector. The titration gives the mercury content of the sample examined to the nearest microgram. The lower limit of the concentration that can be detected is governed by the volume of the sample taken.