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HISTORY OF THE MERCURY FLASH SrNm 1927 the common unit for measuring and pric- ing mercury has been a 76-pound flask. Of the several explanations for this unusual unit, three seem important enough to mention. According to information from the U. S. Bureau of Mines, the 76-pound unit was adopted in the United States for the sake of uniformity and agreement with Spanish practice. When the metric system was first used in Spain the content of a standard mercury flask was fixed at 34.5 kilograms, which is equivalent to 76.06 pounds, approximately 76 pounds, one ounce. Since the commercial production of mercury probably originated in Spain it seems reasonable to believe that the 34.5 kilogram unit had its beginning there. Before the adoption of the metric system there were a number of different "nounds" or "libras" in use in different oarts of Spain and for different commodities, just as there are different bushels used in the United States today. However, there was a legal apothecary's libra which was equivalent to 0.7606 pound avoirdupois. This unit weighed thre+fourths as much as the legal avoirdupois pound, which was 1.0143 U. S. avoirdupois pounds. The early uses of mercury were largely confined to the medicinal field, and therefore early purchases of this metal may well have been on the basis of the apothe- cary's pound. Consequently, it seems possible that our 76-pound unit had its origin as 100 Spanish apothe- cary's pounds, especially in view of the common metric practice of using a multiple of ten, in this case the quintal or hundredweight, to make larger metric units. Secondly, it has been suggested that the 76-pound weight unit for mercury had its origin as follows: Taking the bushel measure as equivalent to 2150 cubic inches and water at the conventional 250 grains per cubic inch, we find there are 537,500 grains per bushel; DELMAR K. MYERS The Pennsylvania State College, State College, Pennsvhania 76-pound unit is that it is related to a Spanish weight, the arroba. This Spanish unit is usually equated to 25.36 avoirdupois pounds. Three of these units would, therefore, equal 76.08 pounds or almost exactly 76 pounds, one ounce, the exact contents of a flask of mercury, rather than 76 pounds as it is usually stated. The flask itself, as may be seen in the illustration, is approximately 18 inches long and 4 inches in diameter. It is made of cast iron and fitted with a threaded iron plug. The weight of this container, plus the three arrobas of mercury, is about all a man can be expected to handle conveniently and regularly. Perhaps it would be more nearly correct to say all that a slave could handle, as the unit was used as early as Roman times when slaves and prisoners of war worked the Almaden and Idrian mines in S~ain. at 7000 per pound we thenget 76.7 po;nds as the Those persons associated with cinnabar mines and weight of a bushel of water. At first this rather close mercury distilleries in California, as far back as they approximation seems logical and probable since several can remember, can recall no other unit ever having .of our scientific constants are based on water as the been used, and the standard flask in use today contains standard. However, it would seem from the facts 76 pounds, one ounce. It is true, however, that from given above that this explanation is much too modern some of the smaller mines the metal is sometimes sent t o be accepted. out in sheepskin bags holding 55 pounds of mercury, The most probable explanation of the origin of the but this unit does not appear in commerce.
