INDUSTRIAL AND ENGINEERING CHEMISTRY-
rule these operations involve from 10 to 30 seconds, and the furnaces are not cooled much more than 50” t o 100” C.; if, however, a bulky charge is placed in a furnace, or the top is left off for a longer time, a proportionately longer interval must be allowed for the return to operating temperature. Furnaces are wound for operation within a given temperature range directly on the line current without external resistances, except as noted in connection with platinum windings. External resistances can be a nuisance in a husy lahoratory, because when a hot furnace is required in a hurry the tendency is to cut out all the resistance to ensure rapid heating; if one forgets t o adjust the resistance a t the proper time on a furnace that is overpowered for direct operation, something is bound to melt, necessitating the rebuilding of the furnace. Most of the heat loss from a crucible furnace built aa described occurs at the top. The clay, H-W refractory, and Sil-0-Cel covers are convenient to handle and are highly efficient for their size, but the Kanthal-wound furnaces will attain higher ultimate temperatures if insulated with the more cumbersome type of cover used on the platinum-wound furnaces. In addition, however, to the added inconvenience of such a bulky top, the practical operating temperature of the furnaces is not increased sufficiently to warrant such a cover when the furnaces are being constantly opened and closed.
Just as important for the life of the furnace as the resistance winding is the method of connecting the ends of this winding to suitable terminals or binding posts; improperly made connections will cause an early failure of the wire near the point of contact because of a tendency to arc, because of embrittlement due to recrystallization of the wire, or because of a tendency toward accelerated oxidation a t this point. Connections are best made a t a point outside the furnace so as t o afford maximum air-cooling of the terminals. For this purpose, the ends of the winding are led through Alundum tubes and brought through the shell at some convenient point: they are then attached to metal terminals rigidly fastened to a bracket supported b y the shell. The metal terminals, shon-n in Figure 3, should be large enough to dissipate heat rapidly from the ends of the winding; as set screws used to make connections often freeze upon being heated, and tend to oxidize rapidly, i t has been found more convenient to omit screws, drill the terminals slightly larger than the resistance R-ire, crimp the wires, and force them into the holes. Suitable connector plugs are then attached to the terminals. A number of furnaces were built in which connections were made inside the shell and the terminals protruded through the shell; these were very compact and neat in appearance, but all failed within a short time at the connections.
Acknowledgment The u-riters wish to express their appreciation to J. A. Upper for all the electrical measurements and for his help and suggestions in improving these higher temperature furnaces. A small furnace embodying these ideas is now being tested with inorganic microcombustions.
Literature Cited (1916).
(2) Driver-Harris Co., Harrison, N. J., ”Nichrome”. (3) Fahrenwald, F. .1., J. INn. ENG.CHEM.,8, 436 (1916). (4) Harbison-Walker Refractories
Co., Pittsburgh, Penna., “Re-
(5) Hillebrand, W. F., and Lundell, G. E. F., “Xpphed Inorganic AnalysiP’, pp, 396, 544, 724, 734, New York, John Wiley & Sons, 1929
(6) Ibid., p. 299, footnote 7. (7) Hoskins Manufacturing Co., Detroit, Mich., “Chromel”. (8) Johns-Manville Co., New York, N. Y., “Refractories”; Celite Products Co., New York, N. Y . , “Sil-0-Cel”. (9) Johnson, C. M., “Chemical Analysis of Special Steels”, 3rd ed., footnote p. 504, New York, John Wiley & Sons, 1920. (10) Kanthal A-B, Hallstahammar, Sweden, “Kanthal and Resistance Materials”; C. 0. Jelliff Mfg. Corp., Southport, Conn.; Canadian SKF Co., Toronto, Ont. (11) Lundell, G. E. F., Hoffman,J. I., and Bright, H. A., “Chemical Analysis of Iron and Steel”, pp. 258, 576, New York, John Wiley & Sons, 1931. (12) Ibid., p. 163.
Peters, F. P., Trans. EZectrochem. Soc., 68, 29 (1935). (14) Saunders, L. E., et al., Zbid., 26, 233 (1914). (15) Walden, L.,J. Sci. Instruments, 16, 1, 92 (1939). (16) Winne, R., and Dantsizen, C., J. IKD.ESG.CHEM., 3, 770 (1911). (13)
A Compact Gas Saturator AARON E. RTARKHAM University of Washington, Seattle, Wash.
(1) Blum, W., J . Am. Chem. SOC.,38, 1282
VOL. 12, NO. 2
SOME xork on gas solubility, the gas saturator described here was found more satisfactory than the commercial Friedrichs or Milligan gas JTashing bottles. The accompanying figure shows the apparatus. All the construction is of glass, blown to form one piece. Tube A , of 3-cm. diameter, is sealed at the top to the egg-shaped bulb, C, and at the bottom fits into the conical flask, B. Several holes, about 2 mm. in diameter, are made about 5 mm. from the bottom of tube A. The bottom of C opens into tube D, which extends about 2 mm. beloiv the bottom of A. A spiral of tube E, about 5 em. in diameter and closely wound, is sealed to the side of C and to the top of B. Tubes G and F make connection at the top of A and C, respectively, and are extended t o make convenient connections to the gas supply and to the apparatus requiring the gas. A short tube, H , is sealed to B near the bottom, t o facilitate emptying and cleaning. Tubes E, F , G, and H are about 7 mm., while D is M M about 5 mm., in outside diameter. When used, H is sealed 1 off bv a rubber tube which is pfugged. The proper amount of solution (about 200 cc.) is placed in B. Gas is blown through G, goes down through A , and bubbles out through the small holes near the bottom of A. As it goes up to the top of B and into the spiral, which is about 1.50 cm. long, each bubble of gas pushes a plug of liquid into the spiral ahead of it. As the gas bubbles pass up the spiral, the tube walls are kept wet, giving intimate contact between gas and liquid. The gas and liquid both enter C, the liquid runs back down tube D , while the gas leaves through F. I t is easy to fill the a p paratus under vacuum, thus preventing solution of air during the filling. The whole apparatus can be immersed in a thermostat. Weights are necessary to prevent tipping.
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