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ANALYTICAL CHEMISTRY
glass seat which frequently occurred at the plwe of contact with the metal needle. This disadvantage has been eliminated hy making the apparatus entirely of‘ stainless steel. The details of construction are given in Figure 1. Gas enters the valve at the right, through the horizontal capillary, passes through the conoidal seat, and leaves by way of the downrvard slmting tube at. the left. Flow of gas through the valve is precisely regulated by turning the needle provided with a large knurled disk, Fittings are made gas-tight by rneans of a rubber alceve, but a droplet of mercury is used at the point indicated as an additional precaution against leakage. The mercury is introduced through the horizont’al capillary. The valve must not leak with working pressures up to and including 10 pounds per square inch. The all-metal needle valve described here is lighter in weight than the glass-metal t,ype which requires the use of several grams of mercury as a seal. The diameters of the tubes follow the recommended specifications for the D n n w stopcock (5, 6 ) .
iCKNOWLEDGMENT
The sketch of the needle valve (Figure 1) was made by H, T. .%dams, Kimhle Glass Division o f Owens-Illinois Glass Company, Vineland, S . J. LITERATURE CITED
(1) Heiahbeig, E,. B., and Southworth, L., I m . EN(:.CHEM, (2, (3)
(4) (5)
(6)
.\NAI,.
ED.,11,404(1939). Niederl, J. B., and Niederl, V.,“,Micromethods of Quantitative Organic Analysis,” 2nd ed., p. 80, New York, ,John Tiley & Sons, 1942. Pregl, F., “Quantitative Organic Microanalysis,” tr. from 2nd revised and enlarged German edition by Ernest Fyleman, p. 81, London, J. & A. Churchill, 1924. Roth, H., “Quantitative Organische Mikroanalyse,” 5t,h German ed., p. 80, Vienna, Springer Verlag, 1947. Hoyer. G. L., Alber, H. K., Hallett, L. T., and Kuck, J. d.,IND. E x . CHEM.,A s . 4 ~ ED., . 15, 476 (1943). Royer, G. L., Alber. H. K., Hallett, L. T., Spikes, W.F., and Kuck, J. A . , I b i d . , 13, 574 (1941).
RECEIVED March 4, 1949. Presented as part of a report t o t h e Division of Analytical and Micro Chemistry at t h e 114th .1Iwting of t h e ERICAN AN CHEMICAL SWIETY,St, Louis, M o .
large-Capacity laboratory Vacuum Sublimation Apparatus ARTHUR F. HELIN AND CALVIN A. VANDERWERF C’niversity of Kansns Chemical Laboratory, Lawrence, K a n .
URING the courbe oi certain investigations carried out in this laboratorj , it was necessary to purify relatively large hatches of different materials by sublimation. Inasmuch as none of the laboratory sublimators described in the literature (1-8) seemed adequate for the purpose, construction of the apparatus described beloi7 M as undertaken. It has proved extremely useful m d convenient for subliming from 1 to 100 grams of material.
I>
condenser with the crude material. h thermometer, K , is placed in the chamber in contact with the material to be sublimed. The unit may then be placed in operation by application of a vacuum and heating of the resistance coil, B , by means of a variable electric current. Upon completion of the sublimation, the water hose and electrical leads are disconnected and the right-hand stopper is carefully loosened and removed. The left-hand stopper is loosened by gentle motions of the chamber, after which the chamber is slipped off the condenser, the rails guiding its path so that no contact is made between the purified and the crude materials. A clean paper may then he spread below the condenser tube and the product may be scraped off and collected on the paper.
As shown in Figuir 1, the uriit consists of a horizontal jacketed Pyrex sublimation rhamber, H , heated by a resiqtance wire, B , wound around its entire length. Through the chamber runs a straight Pvrex tube, I, parallel with the axis of and considerably longer than the chaml)er, which serves as a water-cooled condenser. The ends of the chamber are closed b y means of rubber The temperature range and the control obtainable in an a p stoppers, C, whic*harc bored, somewhat off center, to allow pasparatus of the dimensions indicated in Figure 1 are shown in sage of the condenser. A glass tube, D, passing through one Table I. stoDDer is used for the vacuum connection. The condpnser tube tapers just beyond the point where it emerges from the assembly to permit easy removal of the stopper. The condenser tube is /’ A \, m a d e longer t h a n t h e chamber in order that it may be clamped rigidly in position a t the end of the apparatus. I n preparation of the apparatus for operation, H and outer jacket (; are removed while the Ieft39 c m _hand stopper is held in place on the condenser tube. The material t o be sublimed is 100 em distributed throughout the length of the sublimation chamber and the apparatus Figure 1. Diagram of Sublimation Apparatus IS reassembled by carefully A . Clamps, %fingered F. Asbestos tape 6. Glass tube, 70 m m . o.d., 65 m m . i.d. B . Heating coils, 23 feet of Nichromc wire, R . and sliding the chamber and S. No. 22 H . Glans t u b e , 60 m m . o.d., 54 m m . i.d. jacket into place using the C. Rubber stopper, size 12 I . Glass tube, 14 m d . 0.d. supporting guide rails, J , J . Supporting rails D . Glasa t u b e , 8 mm. 0.d. K. Thermometer to prevent contact of the E. Vacuum p u m p ronnection
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L----
V O L U M E 21, NO. 10, O C T O B E R 1 9 4 9 Table I. Variation of Temperature with Voltage volts
Tempersture. ' C.
The notable features combined in the apparatus m e its relatively large capacity, the simplicity of its construction and operation, its extreme flexibility, and the short distance between evaporating and condensing surfaces which i t m k e s possible. Portions up to 100 grams of a wide variety of organic com-
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pounds, including such representative materials as 8-hydroxyquinoline (8-quinolinol), p-aminophenol, pentachlorophenol, and pfluorobenaoic acid, have been sublimed successfully in the unit rlnonrihd
:.mad. 7011. Belg., 18, 1138 (1932). (4)Ken&, R., J . pialtt. Chem.. 78,201 (IOOS). (5) Marberg, C.M., J .Am. Chem. Soc., 60, 1509 (1938). (6) Morton, A. A,. M ahoney, J. F., and Richardson. G., IND.ENG. C a m . . ANAL.Ih.,ll.460(1939). (7) Nelson, 0. A., IbG1.. 14, 153 (1942). (8) Pitha, J., J . Chem. Education. 23,403 (1946). Recemeo December 13. 1948.
Analysis of Residual Gas in Electron Tubes with the light Spectrograph R. H. ZACHARIASON Radio Corporation of America, Laneaster, Pa. HE presence of even a small amount of gas in a finished highTvacuum electron tube is generally sufficient cause for factory rejection of that tube. Unwanted gas can he introduced during the manufacturing process in many ways; unclean parts, improper breakdown of oxid'eooated cathodes on exhaust, leaks, hydrogen ahsorption through metal parts, and poor tip-offs are typical causes of gassy tubes. If the composition of the unwanted gas is known, the gas source can often be found and a serious epidemic of gassy tubes prevented. Few of the standard methods of gas analysis are applicable to the analysis of the gas in a finished tube. Standard methods of gas absorption in various reagents are ruled out beoause of the small slze of the sample, which in many cases is less than 1microliter. The difficulty of opening the finished tube and transferring the sample also rules out most methods. Most of the samples are too small for even the mass spectrograph. The method that offers the most promise uses the light spectrograph or spectroscope. When the spectrograph is employed, it is first necessary t o ionize the gas and obtain a visible discharge which can b e focused on the slit of the spectrograph. T h e simplest way of accomplishing this step is by means of a spark discharge, such as can be obtained with .a Tesla coil. The use of the spark coil, however, makes it difficult to obtain a concentrated beam of light because the discharge tends to flicker and be diffused rather than sharp. I n most cases, a more desirable source of light can be obtained by using a high-voltage tramformer and applyingvoltage between two terminals of the tube. This procedure makes i t generally possible not only to control the discharge but to focus the light accurately an the spectrograph slit with little difficulty. A third way applies particularly to cathode-ray tubes and is by far the best when it can be used. In a completed Cathode-ray tube, it is possible to use the cathode-ray gun to furnish 8 stream of high-speed electrons which will ionize the gas and give a concentrated discharge. None of these procedures requires opening the tube and the gas can be analyzed without destroying the tube. After a procedure for ionizing the gas has been selected, the next problem is the choice of a spectrograph. Initially, the author's analyses were made using a large Littrow Band L spectrograph, Eastman I-F plates (specially made for spectrog:aphic work, with high sensitivity in the region of 4500 to 6800 A. and medium cont,rast,),a slit opening of 250 microns, the widest open-
Figure 1. Assembled Equipment
