1038
Table 11.
ANALYTICAL CHEMISTRY Sensitivities for Elements Reported in Table I
5%
of different design were fabricated and have been used for a year in a large number of operations-perhaps 8everal thousand times. One 6ource of supply of graphite blacks suitable for making the graphite-block evaporators is the National Carbon Co., 30 East 42nd St., New York, N. Y. I n SO far as the apertures are concerned, the blocks can he made in any machine shop. -4pertures are made m solid graphite or metal, with diameter to I/* inch such that the bottom of the crucible or dish is nhove the heating surface. For h w t operation, the height or thickness of the block is of such dimension that the solution or liquid level is below the periphery of contact between the evaporator and the container.
m e cleaning 01 tne ceramic surfaces is as rapid as cleaning the steel buckboard. Because the ceramic is white R colored residue from previous samples is readily detected. Cleaning sand, it brush, and cornpremed air were used to clean the surfacea. The very favorable comparieon of the trace constituents found after grinding on the ceramic buckboard with those obtained after grinding in an agate mortar indicates that the ceramic buckboard is sat,iafectory for grinding samples for trace analysi?. Figure 1 *CKNOWLEDGMENT
The authors wish to exprem their appreciation to H. W. Lakin and A. T. Myers of the U. S:Geolopical Survey for their technical nesiEtrtr ngement. LITERATURE CITED
ley Press, Cambridge, Mass., 1950. (2) Barnett, P. R., Huleatt. W. P., Rader. L. F.. and Myers, A. T.. Am. J . Sci., 253, 121 (1955). (3) Fleisoher, Michael. Murata, K. J., Fletcher, J. D., and Narten, P. F.,U. S. Geol. Survey, Cire. 225 (1952). (4) Myers, A. T.,and Barnett. P. R.. Am. J . Sci., 251, 814 (1953). (5) Sandell, E. B., IND.ENS.CHEM.,ANAL.ED., 19, 652 (1947). POBLICATION wtirorired by the Director, U. S. Geological Survey
Graphite- and Aluminum-Block Solution Evaporators C. D. Surano, Analytical Chemistry Division, Oak Ridge National Loborotory. Oak Ridge, Tenn. HE evaporation of aqueou8 solutions which are in contact T w i t h solid matter, perhaps the mast common of d l operations encountered in the sndytical chemistry laboratory, ha8 always been particularly difficult and exasperating. I n B large measure, this problem of evaporation was solved for the cme of the evaporation of solutions, with or without a solid phase, when the materials are containedin beakers, by the development of the so-called Fisher-Maroney, no-hump, solution evaporator [Marone?, J. J., TheLaboratory, 6 , No. 4,62 (1933)l. Because the Fisher evaporator is so efficient, consideration was given to the possibility of applying a modification of this apparatus t o the evaporation of solutions contained in dishes and in crucibles, and to the charring of filter papers accompanying moist precipitates, another technique common to gravimetry. Evaporators of solid aluminum metal, sheet steel, and solid graphite were designed, made, and tested. The evaporators which were fabricated from solid aluminum proved to he satisfactory, hut an evaporator fabricated out of solid graphite wm even more efficient and satisfactory. As B result of these tests, several graphite-block evaporators
The incidence of humping and sut have been completely eliminated by m e use or tnese DLOCK evaporators. Evaporations have proved to be exceedingly fast. I n all cases, the time of evaporation has been reduced by a fnctor of 2 to 3, and even much more,. deDendine on the uurtntitv . of solids contained i n the vessel, These evaporators have been used in the evaporation and boiling of solutions of high boiling point, such as perchloric and sulfuric acids, and i n contact with large quantities of solid matter without incident. Accidental spills v.ll "*lyl. 6'L~..l"c should cause no concern because these two materials are inert t.oward each other. The decomposition of silicon dioxide in the usual hydrofluoric acid-sulfuric acid treatment of residues may he accomplished with speed and completely unattended, without fear of laas of matter due to localized overheating and humping. These evaporators are very useful in the burning offof filter papers i n the usual gravimetric technique. This technique can he improved even more hv the combined use of the block evaoorator and infrared lamps. Combinations of moist precipitate and filter paper in crucibles m&yhe dried a t the full heat of hot plat.es when graphite-black evaporators are used. Graphite-black or aluminum-block evaporators may.be made with any number of apertures, from one aperture up to the full capacity of the hot plate, and may be used with platinum, glass, or porcelain dishes, casseroles, and crucibles. Gang evaporators may be designed with 8 variety of apertures for multiple operations. An example of large scale evaporations is shown in Figure 1. In this operation, perchloric acid is being used with hydrofluoric acid in the dissolution of B silicate rook. Thirty evaporations can he performed simultaneously with two &gang, graphiteblock evaporators an a hot plate which has a rated capacity of 8600 watts. Evaporations with the higher intensity of fumes, on the left-hand side, are a t the fuming stage. Examples of gang evaporators of different sizes and capacities are shown on both sides of the hot plate. I
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B ~ e mo n work performed for the Atomic Energy Commission by Carbide and Carbon Chemicals Co., division of Union Carbide and Carbon Corp.
