ANALYTICAL EDITION
JANUARY 15, 1940
Practical Test of Crucible T o determine the suitability of these crucibles as containers for molten slags, a charge consisting of approximately equal parts of lime, silica, and ferric oxide, which had been found t o corrode and permeate commercial magnesia and magnesite crucibles, was melted in one of the new crucibles. The melting time was about one-half hour. A final temperature of 1500" C. was reached. At this temperature a quiet melt had been obtained, and the slag was in a very fluid condition. T h e gas myas then shut off from the furnace, and the crucible a n d contents were allowed to cool slowly in the furnace. The analysis of this slag, after melting and slow cooling, was found to be as follows: % Si03
51
A polished section showed that this slag contained dendrites of magnetite embedded in a background of ferrous akermanite (2 Ca0.Fe0.2Si02), as shon-n in Figure 5. Figures 6 and 7 are micrographs showing the boundary between the slag and the crucible. This boundary is relatively sharp, and the crucible wall was practically impervious to the slag.
Literature Cited Barrett, E. P., and Holbrook, W. F., IND. ENG.CHEX.,Anal. Ed., 10, 91-3 (1938).
. H.. Trans. Am. EkeJordan. L.. Patterson. A. A , . and P l i e l ~ sL. _
I
trochem.'Soc., 50, 115-24 '(1926). Mehl, R. F., Ibid., 46, 149 (1924). Salmang, H., and Plans, N., Arch. Eisenhiittenw., 6, 341-6 (1932-33).
26.24
Schuette, G. N., Bur. M i n e s Re.& Investigations 2896 (Oot.,
30.66
Swanger, N. H., and Caldwell, F. R., Bur. Standards J . Research.
14 03 21.27
8.53
1928). 6, 1131-43 (1931).
A Vapor-Proof Laboratory Stirrer GEORGE CALINGAERT, Ethyl Gasoline Corporation, Detroit, RIich.
A
VAPOR-PROOF laboratory stirrer with readily available oil-impregnated bronze bearings has been used in this laboratory, in preference to the conventional glass-in-glass mercury-seal bearing, for carrying out reactions which call for stirring in a closed system. This stirrer is a n improvement over the older type since i t can be used for high-speed stirring operations, is neither fragile nor cumbersome, eliminates the use of mercury, and does not t r a p liquid during the operation. 'The oil-impregnated bronze bearings employed in its construction offer enough resistance to the flow of vapor to prevent leakage, even when the apparatus is operated under slight pressure or vacuum, and it operates much more smoothly than the conventional mercury-seal stirrer. The latest and best design, illustrated in Figure 1 (left), comprises a 1.59-cm. (0.31-inch) steel drill rod, A , fitted a t one end x i t h a mixing device such as a small bronze propeller from 2.2 t o 7.5 cm. in diameter, depending on the size of the reaction vessel opening. Such a propeller is obtainable in a variety of sizes from shops supplying parts for toy motor boats. An equally satisfactory type of mixing device is the centrifugal pump illustrated in Figure 1 (center). The combination holder, bearing, and seal is a 25-cm. length of 0.95-cm, (0.375-inch) brass pipe, C, equipped a t both ends with a pressed-in oilless bearing, B , about 1.92 cm. (0.75 inch) long and 1.59 cm. (0.31 inch) in inside diameter. These bearings are available on the market in numerous sizes and from various manufacturers (for example, Bound Brook Oilless Bearing Company, Bunting Brass & Bronze Company, Amplex Division of the Chrysler Corp., Johnson Bronze Company, Nolu Oilless Bearing Company, and Paramount Oilless Bearing Company). A typical setup using this type of stirrer is illustrated in Figure 1 (right). The brass pipe is fitted into the stopper of the flask, and after this has been lined up and clamped, the upper end of the stirrer shaft is connected to the motor shaft by means of a short piece of heavy-walled rubber tubing. Stirrers of this type have been used repeatedly in flasks containing boiling organic solvents without any leakage or deterioration of the bearings. When corrosive liquids are used, the stirrer may be constructed of stainless steel or some other suitable corrosion-resistant alloy.
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bB 'I'
1
FIGURE 1
