AUGUST 15, 1939
ANALYTICAL EDITION
With the aspirator going slowly, the open arm of the T-tube is closed momentarily to start the flow of acid into the reaction chamber, A. It is best that the acid be added slowly with some shaking. When all the acid has been added, the open arm of the tube is closed and a slow stream of air is drawn through to remove all the carbon dioxide. After the apparatus has again reached room temperature, the plugs are attached to B and C and the apparatus is weighed again. The loss in weight represents the carbon dioxide evolved.
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For more detailed general instructions concerning the manipulation, the reader is referred to such textsas Kolthoff and Sandell (I)*
Literature Cited (1) Kolthoff, I. M., and Sandell, E. B., "Textbook of Quantitative Inorganic Analysis," pp. 360-2, New York, Maomillan Co., 1936.
Crucible Support GILBERT E. SEIL AND H. A. HEILIGMAN, E. J. Lavino and Company, Norristown, Penna.
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HE crucible support shown in the drawing offers many advantages to the laboratory in which evaporations, fumings, and ignitions are done in platinum crucibles. When platinum crucibles are heated on a sand bath or supported in a triangle, many determinations are lost because of the spattering of the residue. Moreover, determinations in adjacent crucibles must be discarded because no near-by crucible is free of suspicion of contamination. The creep of salts up the sides and over the top of the crucible during the fuming of a residue is a frequent source of annoyance and error. The salts may bake to the outside of the crucible and become contaminated with the sand of the sand bath. Portions of the baked residue may crack and
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drop off. A crucible support which eliminates spattering and creep is a valuable adjunct to any laboratory. The equipment described in this article supports the crucible so that accidental overturning is impossible. The support is easily cleaned and kept clean and, unlike a sand bath, can be moved as required to any convenient location. Filter papers can be quickly and thoroughly dried without charring before ignition. The time required for carrying out a drying, an evaporation, or a fuming in a platinum crucible is reduced by one half as compared with the usual methods. The authors found, for example, that in doing several hundred fluorspar analyses, the time required for volatilizing the silicon tetrafluoride, fuming t& residue with sulfuric acid, and then igniting the calcium sulfate was cut in half by the use of this support. More important, the creep of the salts up the sides and over the top of the crucible was eliminated. No samples were lost because of creep. The crucible support described is in reality an air bath which distributes the heat around the sides as well as to the bottom of the crucible. It can be conveniently placed on one corner of a hot plate. The authors obtain excellent results with a support placed on an iron plate over a circular gas burner such as is frequently used in kitchen ranges. The size of the support and of the openings can be varied to suit the needs of the individual laboratory.
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The authors use several supports in which twenty crucibles (30-ml. capacity) can be treated simultaneously. The supports are easily made from a piece of soapstone 25 X 30 X 3 cm. (10 X 12 X 1.25 inches) drilled as shown in the drawing. First the 0.6-cm. (0.25-inch) holes are drilled at the center of each circle and at the points indicated on the circumference of each circle. Next the 2.8-cm. (1.125-inch) holes are drilled through the stone, and finally the 3.4-cm. (1.375-inch)holes are drilled 1.25 em. (0.5 inch) from the top of the stone and 0.25 inch from the bottom of the stone. The crucible will rest in the opening, and the heat will go through the holes along the sides of the crucible, thus heating the sides as well as the bottom. The crucible restslow in the opening and cannot be turned over.
