FEBRUARY 15, 1938
AN.4LYTICAL EDITION
establishment of any one property of the cut usually defines, within a narrow range, the rest of the properties a t least for practical purposes. The data in Table VII, for instance, show that as the refractive index of the extract becomes constant, so do also its viscosities and viscosity indexes. They represent different runs of different durations, and not only show that there is no need to carry on the run beyond a t most 5 hours, but also that by simply following the refractive index of the reflux oil it is possible to predict the constancy of quality of the extract.
Acknowledgment The authors xish to acknowledge the help of J. A . Pollock in testing the packing materials, and of H. S. Smith in some of the extraction experiments. This work was made possible by funds contributed partly by the Pennsylvania Grade Crude Oil Association, and this assistance is greatly appreciated.
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Literature Cited Am. Soc. Testing Materials, Designation D287-37, Standards on Petroleuni Products and Lubricants, 1937. .Im. SOC. Testing Materials, Designation D445-37T, Method R , Standards on Petroleum Products and Lubricants, 1937. Cannon, M. R., and Fenske, M. R . , IND. EXQ.CHEM.,28, 1035 (.1936). Cannon, hI. R . , and Fenske, hf. R., Oil Gas J . , 33, No. 47, 52 (1935); Ibid., 34, KO.47, 45 (1936). Hersh, R. E., ,Vat. Petroleum Sews, 28, No. 45, 30 (1936). Hersh, R. E., Fisher, E. K.. and Fenske, M . R., ISD. EXQ. CHEX,27, 1441 (1935). Hill, J. B., and Coats, H. B., Ibid., 20, 641 (1928). hloCluer, IT. B., and Fenske, M. R., Ibid., 24, 1371 (1932). Rushton, J. H., Ibid., 29, 308 (1937). Varteressian, K. A . , Ph.D. dissertation, The Pennsylvania State College, 1935. Varteressian, K. -4.. and Fenskr, 51. R . , IND.ENO. CHEM.,28, 928 11936). Ibid., 28, 1353 (1936). Ibid., 29, 270 (1937). R E C E I V E DOi toher 28, 1937.
Fused Magnesia Crucibles E. P. BARRETT k h W. ~ F. HOLBROOK Blast Furnace Studies Section, JIetallurgical Dirision, Rurcau of 11iiies, 1linneapolis. 3Iinn.
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0 MATTER is of greater importance nor of more con-
cern to the metallurgist and to the operator of a hightemperature furnace than the kind, life, and use of the refractory that forms the melting chamber.
Melting Point The melting point of a refractory material does not tletermine the temperature to which a charge in the crucible may be safely heated. The manner of heating is very iniportant. Kanolt (6) states that magnesium oxide heated under reduced pressure (0.5 to 1.0 em. of mercury) volatilizeconipletely before it melts. When heated a t atmospheric pressure in contact with carbon, magnesium oxide rolatilizes rapidly a t temperatures above 2000" C. If the metal withill the crucible is heated directly by induction in the high-fiequency induction furnace the metal is always hotter than the crucible, whereas if the metal is heated indirectly by conduction of the heat through the wall of the crucible the crucible is always as hot as, if not hotter than, the metal within it Slight amounts of impurities such as bonding materials useti in forming the crucibles may lower the softening point of the crucibles by several hundred degrees below the melting point of the pure refractory material. Roller and Rittenberg (8) found that fused magnesia crucibles fired to approximately 2600" C. in a high-frequency induction furnace sometimes bulged a t the base. They state: This illustrates that there is a region of crucible flow a t high temperatures rather than a sudden melting down."
Reactions of Fused Magnesia with Carbon Swanger and Caldwell (12) suggest that graphite molds Le used in forming the crucibles, since magnesium oxide does not form carbides and the crucibles can be heated to 1800" C. in the molds in which they were formed. Kanolt (6) found that magnesium oxide when heated a t atmospheric pressure in contact with carbon volatilized rapidly a t temperatures above 2000" C. Roller and Rittenberg (8) reported that
dense fuineb were evolved when iiiagiiesium oxide was heated in (*ontact with carbon a t temperatures of ahout 2500" C.
Methods of Making Small Crucibles Processes for the manufacture of magnesia crucibles have been described by Burgess and Aston ( I ) , Cain, Schranim, and Cleaves (Z), Yensen (14),Fergerson (S),and Watts ( I S ) . Mehl (7') states: "In all of these processes the purified magnesium oxide was first shrunk by heating to a temperature near 1600" C., then ground and pressed into a mold under high pressure, and finally heated to a temperature a t which sintering occurs, with consequent roliesioii of the rather coarse particles of magnesium oxide." Nehl mixed a thick sirup of diellac in absolute alculivl with the calcined c. P. magnesia and packed the mixture into a braes mold. The core and then the base were removed, and the crucible was dried for several hours in a brisk current of air. The crucible was then removed from the mold and dried for several hours in an air oven at 100' to 130" C. The dried crucible v a s fired in an electric furnace. Jordan, Patterson, and Phelps (6) found that, commercial fused magnesium oxide was not pure enough for preparing crucibles for w e in melting pure metals. Since the chemical reagent grade of unfused magnesium oxide shrinks a great deal xhen heated to 1600" C. it is necessary to calcine it before wing it to form crucibles. They moistened < 100-mesh calcined oxide nith a 2 per cent solution of MgC12.6H20,tamped the mixture into a graphite mold, and fired in the mold at 1600' to 1800" C. The crucibles were very hard and dense and had an almost porcelainlike body or texture. The apparent specific gravity of such crucibles was ahout 3.5. They found that the addition of about 15 per cent of a mixture of equal parts of 100- and 200mesh purified white zirconium silicate incwased the strength of magnesia crucibles. Zirconium silicate often contain* phosphorus. Schuette (10) tamped
