Electrode Holder for Work in Controlled Atmospheres A. M. Pommer and J. F. Abell, U. S. Geological Survey, Woshington 25, D. C.
pH or oxidation potential must he 1. measured in a controlled atmosphere, F
it is not always convenient to use a ruhher-stoppered vessel and insert the electrodes through the holes. Glass electrodes may he scratched during insertioii and, in the case of a permanent setup, electrodes or glass tubes have a t.endency to freeze in thc stopper. For conducting simultaneous pH and oxidation potential measurements in controlled atmospheres, thc reaction jars were providcd with methyl mcthacrylat,e plastic closures suitable for holding electrodes or other devices.
screw
Electrode
O-ring
v
,cover
other drvices inserted through the holder, holes of the desired diamet.er were drilled through the cover plate aiid closure. The holes in the closure werc then counterhored to accept O-rings. Where the device w&s not of a stmdard O-ring size, the diameter of the countcrhore \!-as decrcased to provide the necessary prcssurc for a mal using thc nearest size standard O-ring. The covrr plate then was secured to the disk bjthe screws that retained the O-rings. After the elrxtrodes rere inserted iu the holes, the container was reasonably airtight and could retain some excess presswe. ACKNOWLEDGMENT
A closure consisting of a plastic disk with 3 diameter slightly larger than thc estrrior diameter of the jnr was machined to form a shoulder mith an O-ring croove to fit the inside ~~-dinmet,er of.. t,hP .... Yar. A cover plate was placed on the first disk and secured with three machine screvs. To accommodate electrodes or
TI'. D. 1,ong contributed to the design. W o a ~carried out
8s part of a program conducted by the U. S. Geological Surve? on behalf df the Division d Research, U. S. Atomic Energy Commission. Publiration authorized bv Director. U. S. Gcalogiral Survey.
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Infrared Heating Applied to Differential Thermal Analysis J. A. Hill and C. 8. Murphy, General Engineering Laboratory, Generol Electric Co., Schenectody,
sample holders M and complicated heating systems have been ANY
devised for differential thermal analysis. To fill the need for a simple sample holder and inexpensive heating systems for application t o organic materials, the suitability of infrared heating was explored and an experimental model was designed. Apparatus and Reagents. The allparatus is shown in Figure 1. The .sample holder consists of a graphite cylinder 1.25 inches in diameter and 0.25 inch thick. Two cells were drilled into the cylinder, one to accommodate the reference material and the other, the sample. Thcse were symmetrically located and were 0.157 inch deep and 0.25 inch in diameter. Platinum-platinum (10% rhodium) thermocouples were inserted into the cells through small holes drilled in the side of the cylinder. The temperature-recording thermocouple was placed adjacent to the sample-containing cell. This sample holder was mounted on an inch-thick section of porous mullite refractory brick with a conical hole centered in the bottom for focusing the infrared lamp on the base of the sample
holder. Other portions of porous brick providcd side wall and cover insulation. Alnminum foil inserted inside the cover section completed the sanlple holder assemhly. The heating element consisted of a
Figure 1. Infrared differential thermal analysis sample holder and heoting system
N.'Y.
specially made Gcnera.1 Electric 8-volt, filament infrared heating lamp nith a 4-inch focal point which was utilized in positioning the lamp for maximum efficiency. Highly calcined alnmina was used as the reference matcrial andsample diloent. The 1,4-dihromoheneene N ~ S Fisher Chemical Co. reagent grade material. Experimental. Programmed Iieating was not used. Programmed and nonprogrammed voltage vas snpplied to the lamp; i t was manually controlled by a Variac and voltmet'er to obtain the thermogram in Figurc 2 (left). Programmed voltage was applied by driving the Variac through reduction gears with a General Elertric 4-r.p.m. synchronous induction motor. This technique gave the thermogram in Fignre 2 (right). The temperature was recorded on a Leeds 81 Northrnp Speedomax Type G recorder. The differential thermocouple output was fed to a Leeds & Northrup No. 9835B amplifier, and then to a Leeds & Northrnp Type G recorder. The thermogram in Figure 2 (left) was obtained by applying 4.0 and 6.0 volts to the lamp filament at A and B, respectively. Figure 2 shove two VOL. 31, NO, 8, AUGUST 1959
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