Accessories for the Chevenard Thermobalance Arthur E. Newkirk. General Electric Research Laboratory, Schenectady, N. Y.
HE Chevenard thermohalance is a Trugged, reliable, and accurate instrument for weighing substances while they are being heated [Simons, E. L., Newkirk, A. E., Aliferis, Ifigenia, ANAL. CHEAT. 29, 48 (1937); .Vielenz, R. C., Schieltz, N. C., Kinz, M. E., Natl. Acad. Sci., Pub. 327, 285 (1954)l. Its utility may be increased by addition of several accessories that are easy to make. Furnace Liner and Transparent Top Plate. Substances heated in the thermobalance occasionally decrepitate, boil, or explode, with the result that the interior of the furnace becomes coated and perhaps attacked by the deposit. The deposits may vaporize in later runs and condense on the qua.rtz support rod, causing erroneous results. It is useful to put a liner in the furnace to facilitate cleaning.
The liner (Figure 1) is made of quartz tubing with a 1.5-mm. wall thickness. It has a flared top which supports it in the furnace, and this is ground flat to make a good fit with a clear quartz top plate inch thick. This plate contains a hole, in which is placed a quartz thermocouple well. The clear quartz top plate permits phservation of a sample during heating. Observation is aided by a mirror
which, for convenience, is attached t o the furnace guide rods by an adjustable collar. These accessories are also shown in Figure 1.
Operation in Controlled Atmosphere. The thermobalance is supplied with a translucent quartz tube for n.ork with controlled atmospheres.
4.2 MY OIA.
H
6 Y Y DIA.
10 MY D I A .
Figure 2. Modified sleeve for operation of Chevenard thermobalance with controlled atmosphere
The bottom of this tube is closed with a screw cap with a hole in the center, in which is placed a thick movable sleeve. The sleeve in turn has a hole in the center only slightly larger than the diameter of the crucible support rod. The clearance is kept small to reduce contamination of the furnace atmosphere with air. As it was difficult to adjust this sleeve, a modified version has been constructed (Figures 1 and 2). The sleeve is made of hrass with a thick plating of chromium. The centering screws added to the cap permit precise control of the motion of the sleeve.
Figure 1.
Accessories for Chevenard thermobalance
a. Top mirror and holder. b. Querta liner. c. Transparent quartz top plate with thermocouple well. d. Bottom mirror. e. Modified x r e w cap for controlled atmosphere tube. f. Modified sleeve.
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ANALYTICAL CHEMISTRY
By means of this device and a mirror placed helow it, the alignment may be made easily in a few minutes. It was found, on heating an air-sensitive sample (cadmium sulfide) in nitrogen, that a flow rate of 125 cc. per minute was not sufficient to prevent reaction with the air, but that a flow rate of 250 cc. per minute prevented this side reaction. A clear quartz tube, modeled after the one supplied with the instrument, makes it possible to observe samples during heating.
