INDUSTRIAL AND ENGINEERING CHEMISTRY
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tions may be defined for any mixture of two or more subtances, so that may be made with improved accuracy*
Acknowledgment The author wishes to the and work Of P. F. Kerr, professor of geology, Columbia UniVerSity, in the development of this technique.
Literature Cited (1) Bohlin, H., Ann. Physik, 61,421 (1920). (2) Bragg, W. H., Proc. Phys. Soc. (London), 33, 222 (1921). (3) Brentano, J., Ibid., 37, 184 (1925).
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(4) Brill, R., and Pelzer, H., 2. tech. Physik, 10, 663 (1929); 7 2 , 398 (1929); 74, 147 (1930). (5) Dave>,, Jv, p., "Study of Crystal Structure and Its Applications", pp. 117-18, 1931. (6) Debye, P., and Schemer, P., Nachr. kgl. Ges. Wiss. Gottingen (1915-16); Physik. Z., 17, 277 (1916). (7) Hull, A. W., Phys. Reu., 9, 8 4 , 5 6 4 (1917); 10, 661 (1917). (8) Morse, J. K., J . Optical SOC.A m . , 16, 360 (1928). (9) S t . J o h n , A., paper read a t meeting of American Association for the Advancement of Science ( J a n . 1926). (10) Seemann, H., Physik. Z., 20, 169 (1919). (11) Keider, H . B., and Milligan, W.O., J . Phys. Chem., 38, 513 (1934). (12) Ibid., 44, 1081 (1940). (13) Wyckoff. R. W.S . , 2 . Krist., 59, 55 (1923).
Electrical Ignition of the Spectrographic Arc FRANK G. BROCKMIN AND F. P. HOCHGESANG, Socony-Vacuum Oil Company, Inc., Paulsboro, N. J.
I
N A P P L Y I S G the Hasler and Harvey (1) method of a
high-streaming-velocity arc to the analysis of brasses the authors experienced considerable difficulty in obtaining reproducible exposures free of objectionable background. I n this method the sample is completely consumed in a direct current arc in less than 10 seconds, so that exposures of 8 seconds were used. W t h such short periods, the time for manually striking the arc represented a n appreciable fraction of the exposure time and the incandescent electrode ends produced background that varied with the rapidity with nhich the operator succeeded in separating the electrodes. Below is described a circuit which enables one t o strike an arc instantaneously and with the electrodes separated at the working distance. The system operates so satisfactorily that in this laboratory i t is used as the sole means of striking the direct current arc. It also serves t o maintain the arc with difficultly burning materials in the electrodes. I n this scheme a high-potential, high-frequency voltage of low energy is superimposed upon the direct current supply, so that the gap is readily bridged. Once bridged, the arc is
Circuit
Circuit
f
2
n
FIGCRE 1. CIRCEITDIAGRAMS A . Direct current ammeter, 0 to 15 amperes R . Resistor 17.5 35 and io ohms LI. Filter cdoke. '116' turns 12.0-cm. (4.75-inch) diameter, 12 turns per inch, 16-gage bare coiper wire on threaded insulated form CI 0.03-mfd.. made from window glass and copier foil, immersed in oil; 39 electrodes, each 15 X 18.75 cm. (6 X 7.5 inches) ca 0.002 mfd. Cornell-Dublier mica capacitor, 12,500 volts direct current maximum CI. Same as Cz GI. Analytical gap 0 63-cm. (0.25-inch) diameter brass rod, 1.56-mm. Ga. Auxiliary ga (0.0625-in& gap Ti. 110/8000 volts 250-volt 60-cycle Thordareon transformer Ta Air core tradformer, Barker and Williamson type 80-T1 (Lz 2 turns, LI26 turns)
. .
.
maintained b y the direct current supply. Pfeilsticker (2) has described a n interrupted arc in which this type of ignition is applied. This ignitor will strike the 250-volt direct current arc with pointed or flat-ended carbon electrodes up to 9.38-mm. (0.375inch) diameter (the largest available here) at 5-mm. separation with any of the three values of series resistor R. Larger gaps can be ignited if the limiting resistor is set to lower values (a 10mm. gap will be ignited if R is reduced to 17.5 ohms). Iron arcs are ignited with more difficulty. However, the authors have found it convenient to produce a reference iron spectrum by using an iron and a carbon electrode (upper electrode carbon, negative; lower electrode iron, positive). This combination is ignited as readily as a carbon arc. Copper arcs are intermediate in ease of ignition-. g., a 5-mm. gap will be ignited if R is either 17.5 or 35 ohms. Either circuit 1 or 2 in Figure 1 performs satisfactorily. Circuit 1 is used here because it requires one less circuit element. CIRCUITS. In circuit 1, CZ, Lz, GPis the conventional spark high-frequency generator. CZis charged by T I to the breakdown potential of gap Gz and then discharges thrqugh Lg, followed by an oscillatory discharge, the frequency of which is determined by C2 and Lz. Depending upon the separation of G2, the breakdown of this gap may occur one or more times in each alternation of the 60-cycle supply. During the oscillatory discharge a voltage is induced in Lt I\ hich is equal to that across LZmultiplied by the step-up ratio of Tz. This voltage appears across the analytical gap, GI, because the impedance of C1 to the high-frequency current is very small: GI is thus broken down. Inductor L1 serves to isolate the high-frequency energy from the direct current line since the impedance of L1 is large a t the frequencies used. The operation of circuit 2 is similar in the essential details. I n the authors' arrangement, the natural frequency of the CzLzcircuit is about 4 megacycles. At this frequency the reactance of Ct is 1.3 ohm while that of L1 is about 16,000 ohms. The step-up ratio of T Zis 13. Resistor R is the customary series resistor to limit the arc current. The filter choke, L,, is located a t some distance from 2'2 and is positioned so that Ll and T zare not in inductive relation. Since the frequency of the ignitor circuit is high, it is im ortant to keep all leads, including those to the arc stand, as sgort as possible. The energy in the spark produced across GI is small and is negligible when compared with the energy dissipated in the arc from the direct current line. All spectra produced have been arc spectra.
Literature Cited (1) Hasler,
M.F., a n d Harvey, C. E., IND.ENG.CHEM.,ANAL.ED.,
13, 540-4 (1941). (2) Pfeilsticker, K., 2. Elektrochm., 43, 719-21 (1937).
