Furnace for Microdetermination of Oxygen AL STEYERMARK, MICHAEL J. MCNALLY, W1 RICHARD NIVENS, A N D FRANK P Hoffmann-LaRoche, he., N u t l q
URNACES suitable for the microdetermination of oxygen Fin organic compounds by the Untereaucher method must be ahle to maintain an operating temperature of approximately 1120' C. with little variation (2). This problem has occupied the )types attention of a number of workere, and a variety ( I , $4of of furnace have been employed in this country.
Bluise el 0 6 . 1.1 U D U uusu a IU~UWS W L Y U UWWL ~ r n u nr~ ~ ments, equipped with automat,ie temperature control. The Engineering Co. which built this furnace later constructed a modified unit, using chromium-iron-aluminum-cobalt. alloy (Kanthal), which is now commercially available (Lindberg Fngineering Co., Chicago, Ill., and Arthur H. Thomas Co., Philadelphia, Pa.). Walton, McCulloch, and Smith ( 4 )use a furnace in which the hesting element is 90% platinum and 10% rhodium wire. Willits and Ogg (6) a180 use heatine elements made of
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ANALYTICAL CHEMISTRY
590 supplied through manipulation of the variable transformer in order to produce the same current consumption as when new. This indicates that under the conditions of operation of the short burner, its resistance gradually increases. However, the constancy of temperature in the short burner is of no great importance, as other operators have merely used a hot gas flame for this purpose ( 1 ) . The long burner has been kept a t the operating temperature even when not in use, because the blank values for the determination did not vary during the day but did vary if the long burner cooled somewhat during the night. DETAILS OF CONSTRUCTION
1
In%”LONS BURNER
SHORT OURNER
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1
____ TAPER
l73k ~/z./I%
BURNER
Figure 3.
LONQ OURNER SHORT B U R N E R
Heating Elements I
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I I c--i , I 1 i l i The long burner was niadefrom a 2 kv.-amp. transformer with a 220volt primary winding. This transformer was purchased without a secondary winding, so that one of the desired sizecould be built. The secondary winding was made from 0.5 X 1.5 inch copper bus bar SPUR GEARS bent to fit the primary core. At some distance from the heating element connection was made to a 2 X 2 X 3 inch brass block. The block ties the element to the transformer and, as it is water-cooled, it actsasacoolingpoint to prevent heat transferrence from the element to transformer. Figure 4. Driving Mechanism All joints must be tight. Silver solder is used on all joints except where connection to the block is made: four 3/a inch brass cap screws are used a t these points. The heating elemenis SUCCLV are made from sections of 3 / 8 inch I.P.S. Inconel pipe, so CVOLCS soldered to two stainless steel ends bored out to fit the pipe. .Is the units operate under low voltage and high amperage, extreme care must be taken in making the connection of t KVA I O L A O V TRAMS o*o URN€ each joint. These end pieces are also machined to hold TRANS Et0 VOLTS I three concentric refractory tubes with air spaces between 210 VOLTS them, which act as insulators for the Inconel pipe. The outside of the unit is wrapped with asbestos tape. The element (Inconel pipe) of the long burner is tapered from the inside of the stainless steel end to within 3 inches of t UVA VARIABLE e K V A VARIABLE the center on both ends. This changes the resistance of VOLTAOE TRAMS VOLTAOL T I A N 8 the sections of the element so that the same temperature throughout may be maintained, and strengthens the center I ’ of the element. The taper runs from nothing in the center Figure 5. Electrical System to 1O in 3.5 inches on each end. The short burner is simila1 to the long, except that a 1 kv.-amp. transformer is Burner trans voltages shown at no load used. During operation at 1120” C., the short burner diaiis 620 ampeies a t 0.8 volt, and the long burner, 480 shows the relationship between the two burners and their caramperes a t 1.45 volts. Keep the ammeters outside the influence of the magnetic field set up by the burner circuits. riage system, Figure 3 gives the details of the heating elements, Both burners are mounted on tracks with wheels. The long Figure 4 gives the details of the r o r m drive, and Figure 5 shows burner is held in position by means of a tension spring, which the electrical system. permits it to be moved forward to the right several inches. The short burner is mechanized. I t travels forward 6 inches in 25 ACKNOWLEDGMENT minutes and returns the same distance in 8 minutes. K h e n the short burner comes in contact with the long burner, it pushes the The photograph was prepared by Carmine Auricchio and latter forward to the right about 2 inches before its motion is reFigures 2, 3, 4, and 5 were prepared by Peter Widmer. versed. When the short burner then travels to the left, the tension spring causes the long burner to return to its original posiLITERATURE CITED tion. The mechanization is accomplished by means of two screws fastened to the bottom of the short burner, one for the ( 1 ) Aluise, V. A , , Hall, R. T., Staats, F. C., and Becker, W. IT., ~ ~ N A L . forward motion and one for the backward motion. A toggle bolt CHEM.,19, 347 (1947). screw action arrangement is used to change from one screw to (2) Aluise, V. A, et al., I b i d . . 23, 530 (1951). the other a t the extreme ends of travel. Power is supplied from (3) Kuck. J. A,, private Communication. a fractional horsepower, 1 r.p.m. gear head motor (Model SG-25 (4) Walton. W. IT., McCulloch, F. IT., and Smith, W. H., J . ReFlexo action motor) made by the Merkle-Korff Gear Co., 213 search S a t l . Bur. Standards, 40, 443 (1948). S o r t h Morgan St., Chicago, 111. ( 5 ) Willits, C. O., and Ogg, C. L., private communication. ~
i l
Figure 1 shows the photograph of the entire setup, Figure 2
RECEIVED February 19, 1951. Accepted July 5 , 1961.
