Apparatus for Vacuum Sublimation. William K. Noyee, Uni. versity of Arkansas, Fayetteville, Ark. HE
apparatus described here is easily constructed from itema
Tusually found ingrams. the laboratory, and has been satisfactory for The distance that the vapors must samples up to 10
travel is relatively short, and the removal of the sublimate from the receiver is not difficult. The material is sublimed from a flat dish ( I ) rather than in a horimntd tube as described by some workers (8-4). The general scheme of the apparatus is s h a m in cross section in the diagram.
With good connections at, the stopper, tho vacuum attainable is limited only by the pumping apparat,us available. However, vxuum desiccators are not gunranteed to withstand a high va+ uum, and sufficient safdy precautions should he taken to protect the operat.or in the event of II collapse. LITERATURE CITED (1) Carothers. W. H., and Hill, J. W.,J . Am. Chem. Soc.. 54, 1557 (1932). (2) Helin, .4. F., snd Vhnderwerf. C. A,, ANAL.CXEM.,21. 1284 (1949).
(3) Morton, A. A.. Mahoney. J. F., and Richardson. G.. IND.ENG. CHEM.,ANAL. Eo.. 11, 460 (1939). (4) Pitha, J.. J . Chem. Educalim. 23. 403 (1
Porous Cup Electrode Drilling Jig. I.. E. Owen, NEPA Project, Oak Ridge, Tenn.
A
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jig has been developed to simplify the prohlem of fabricating reproducible porous cup eleetrodes for use in
spectrochemid analysis. Basically, the jig is an adaptation of the principles used by Feldman a t the Oak Ridge National Laboratory [Feldman, C., ANAL.CHBM.,21, 104 (1949); U. S. Atomic Energy Commksision, AECD-2392 I. Improvements include simplified design, dust-frec operation, and elimination of the prohlem of electrode breeakitgr. The jig also provides a convenient nieans of rcproducing the depth of the drilling cut. The vacuum desiccator has a tuhulated side and an inside diameter of approximately 160 mm. A small, 4ineh (10-em.) hot plate is made suitable for use in the desiccator hy removing the control handle. (As this control is removed, a hot plate with a defective thermostat may be used.) To deoresse further the 6pace required, the lead wires are attached to the prongs of the hot plate by means of the hare clips removed from the usual socket conneotor. Two or three thioknesses of asbestos paper are placed between the prongs. The leads, of No. 16 single-strand copper wire, enter the desiccator through the rubber stopper on opposite sides of the stopcock. They are forced through the stapper after initial holes have been made with a stiff iron or Chrome1 wire. The bare leads inside the desiccator may he insulated by threading glass beads on the wires, hut because they cannot be touched while the apparatus is in use, only normal care is necessary in arranging these wires. The usual type of insulated wires connect these leads to the variable transformer. The latter is indicated schemitticitlly in the figure, hut the details of the connections are not shown. A setting of 10 to 30 volts normally gives sufficientheat. As shown in the drawing, a spacer is used hettieen the heater m d the borosilicate glass Petri dish to prevent local overheating of the sample. A copper ring from a water bath is suitahle for this purpose. Several squares of wire gauze may he used to support the heater a t the proper height. A small amount of curvature in these squares gives enough flexibility to dlow the dish and the desiccator lid to he kept in contact without danger of breakage. The dish is 100 mm. in diameter and 10 to 20 mm. in height. The distance the vapors must travel i s from 10 to 30 mm., depending upon the curvature of the lid as nrell as the height of the dish. The desiccator lid is coaled with a stream of water, because the inner side of the lid is the receiver. For this purpose the desiccs, tor may he supported in a sink or placed in a large pneumatic trough which has been provided with a drain. The stream of water spreads out evenly over the glass if the top of the lid is clean and free from grease. The cooling is adequate to prevent the escape of any appreciable amount of vapors from directly shove the Petri dish. The tuhulstion on the side extends out a sufficient distance to keep the water from the wires and stopcook. On completion of the sublimation, the pressure is equalized, the lid i s removed, and the crystals of sublimate adhering t o the underside are scraped loose. A watch glass is plxed over the material and then the lid and the watch glass are quickly inverted together. This prevents contamination of the produot without the necessity of removing the grease from around the lid. 1581
For use, titic jig i ~ i g u r n11 u pieceu uu um unu pm:aa ueu ana connected to a vacuum cleaner with a section of flexible hose. The nrem is adjusted for maximum travel with the drill touching
msitive positioning gripis desired.
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me made to full depth during thcdrilling operation.^ Construction dctnils of the jig are shown in the exploded view
ANALYTICAL CHEMISTRY
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(Figwe 2): Block B serves as the bottoln of the electrode hole a dust chamber, and the vacuum hne connq action. electrode Four hale smail withhoies the drilled in a clover-leaf pattern connect t h.e dust chamber in this piece. Hardened drill rods ground to the proper height BE inserted in this block ;iIS depth guides.
the solvent used, use of heat-resistant glass in constructing such equipment for use with liquid ttmmonia is almost precluded. Need for B more versatile and convenient apparatua led the writers to develop a mechanical closure far the ends of the Faraday tube, as shorn in the diagram. The tube proper i8 constructed in the usual way of 1-inch
10iitr~idediameter) dlass tubinn. A male. standard-tswr mound ~~
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joint of appropriate size-for &le, 24/40-is m i e d t0 each limb of the tuhe ns suggested in the figure. The female portion of the joint is then sealed off to form 8 cup of convenient s i ~ e , which ~ R k V affixed to the end of the Faradav as a . rammatus .. closure in the manner shown. This cup, provided with 8. closing plug, may be used as a sepavste weighing vessel for materials sensitive to air or moisture. After t,ho weighing operation, the Faraday tube m y be closed much more rapidly than by the old-style seal-off technique, so that the manipulation of senfiitive materials in greatly facilitated. It is necessary to place tbrce or four layers of tough cloth imide the bmss collar, 8,that bolts around the constricted neck of t.he tuhe. The detail of the brass fittinm is shown in the diagram. The'ground joint formincg the clos
