A Briquetting Press anc1 Electrode Loader for Spectrochemi.cal Analysis H. C. HARRISON A ND C. C. RALPH Oregon State Department of Geology and Mineral Industries, Portland, Oregon ~
An inexpensive and easily constructed apparatus is described, for briquetting a powdered sample for spectrographic analysis and loading the briquet into an electrode crater without subsequent manual handling. The apparatus minimizes eontamination and loss of sample, as well as danger of electrode breakage upon loading.
It has a 0.25-inZh inside diameter which is threaded through the head end to a depth of 0.5 inch.. The upper end is beveled flat to fit tightly against the briquetting mold. The bolt is screwed un tight throueh the center of the base. The PlertrodP height-adjuster, &, is a threaded steel rod 0.75 inch in length and 0.25 inch in diameter, at one end of which is a knurled nut, F , 1 inch in diameter and 0.25 inch thick. The adjuster screws into the electrode holder from below. The briquetting mold, G, is a cylindrical piece of 0.875-inch steel rod 2.375 inches in length. A threaded hole 0.5 inch in ~~~
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end of the mold. A"OS88-inch hole tb bored in the center of the
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AMPLES submitted for spectrochemical analysis are often m the form of powder or material which must be
brought to a powder in preparation for the analysis. This is particularly true in the case of rocks, ores, slags, refractories, ashes, residues, ceramic products, and pigments. The dried residue of a dissolved metal or alloy is also sometimes used for analysis. When a powdered sample is placed in the crater of a carbon or graphite electrode, some difficulties may be encountered. An unpacked sample requires a deeper electrode crater than a tightly packed sample, and an excessive amount of electrode wall must be consumed if the sample is burned to completion. A powdered sample placed loosely in the crater does not burn so uniformly as a sample packed in the electrode under pressure. A light and fluffy powder, or one containing certain compounds, tends to be blown from the crater during arcing. Considerable time is often spent in transferring a weighed sample to the crater without any loss of sample. F'reburned electrodes tend to be fragile and extra care must be taken in filling them. Packing the powdered sample into the electrode crater or briquetting the sample into a firm pellet and placing the pellet in the crater has become common practice. The packing operation is performed by means of a steel rod ( 5 ) ; and the briquetting is done with the aid of a punch and die (a, 4), a micro pellet press, or a briquetting press recently described (1). In all these briquetting methods the pellet must be handled in placing it in the electrode crater. The apparatus described here briquets the sample, discharges the pellet directly into the electrode crater, and presses the pellet firmly into the crater without subjecting the pellet to handling by the operator. Repeated checks have shown a negligible loss of sample during these operations. The apparatus is inexpensive, requires very little metal for its construction, and can be easily built in any well-equipped machine shop. The sample to be hriquetted may be a powdered sample or a mixture of sample and other material added to serve as arc stabilizer, binder, or carrier of the internal standard. Electrodes prepared by means of either of the two most commonly used electrode cutting tools (3, 5 ) may be used.
a t the bottom of 'the mold and seuarates the tou of the electrode holder from the bottom of the O.iS8-inch hole tn the mold when the mold is screwed down firmly over the electrode holder. A tool steel rod, J , 0.188 inch in diameter and 2 iiiclies in length, sliahtlv concave at the lower end. and havine a head. K . at the upperknd made of a circular piece of 0.25-inch steel 1.44 inches
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hisuettins hold- is removed from the electrode holder and the plunger is removed from the mold. A 0.25-inch spectroscopic electrode, less than 1.25 inches in length, having square-cut ends and a crater of desired depth, is nlaced in the electrode holder with the crater end am. h u t noi extending above the top of the electrode holder. Thi hold is screwed down over the electrode holder, the steel plate is placed in its slot, and the mold is tightened. The electrode is
A
Apparatus uatns DESIGNDETATM.Figure 11 shows the construction and nsssemhled. Figure 2 shows the apparatus assembled and unsssemhled. The base, A , is a circular piece of 0.25-inch steel plate, 2.75 inches in diameter, inchen diameter. supported sunnorted by three 0.25-inch steel legs, B, 1 in inch in length from the bottom of the base. The electrode ich hexagonal hesd, D, holder, C, is a hollow bolt with a 0.75-inch
B FIGURE 1. CONSTRllCnON OF . b P A B A T n S
lvly
IS, 1943
ANALYTICAL EDITION
467
slight pressure on ges the pellet into idditionsl pressure o the crater. The e electrode holder 1s turned up until ts sufficiently from iolder to be easily
FIGURE2
,ribed is fitted to ,meter with drilled inch, but dimenir construction of d to electrodes of i s is easy to take d with the aid of cleaner. Fragile, by easily be filled wimouc wreaiung. i n e samples may be briquetted by hand pressure or by means of a press .~ operated under known pressures (4).
BaIQuEnmc PRESS,UNASSEMBLED AND ASSEMBLED
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raised by turning the height adjuster until the top of the electrode presses firmly against the bottom of the steel plate. The powdered sample or sample mixture is placed in the 0.188-inch hole in the top of the mold, using the tap of the mold as a funnel, and is brushed into the mold with a camel's-hair brush. If it is desirable that the sample not touch the upper part of the sidewalls of the mold, a small glass funnel may be used to introduce the sample into the bottom of the mold. The plunger is placed in the mold and pressure is applied t o the plunger head, molding the sample between the bottom of the plunger and the top of the steel plate, I. Thespringraisestheplungerfromthesamplewhenthepressure is released. The mold i8 loosened one turn, the steel plate is removed, and the mold is screwed down until the inside of the mold is in firmcontact with the electrode holder and the
W. T.OLSON AND R. A. SPURR National Advisory Committee for Aeronautics, Cleveland, Ohio
A
N ALLGLASS pump, which is leakproof and simple in
construction, has been found satisfactory for circulating gases or liquids in an experimental apparatus. The pump is a reciprocating piston with two check valves arranged as indicated in Figure 1. Features of construction are the mercury-sealed 5-ml. Pyrex hypodermic syringe that serves as a piston, the vacuum-operated reciprocating motor of the automobile windshield-wiper type, and the mercury-loaded glass check valves. The check valves, which are bulbs 10 mm. in diameter on a 15-mm. length of 4mm. tubing, are ground to form a gastight seat on 8-mm. tubing. A small amount of mercury sealed into each check valve adds weight and ensures mpid and secure seating of the valve. Mercury from the seal around the plunger does not penetrate the piston. The pump delivers gas a t 230 ml. per minute against a head of 1 em. of mercury; the limiting head for gas is 25 em. of mercury. The piston with its mercury seal is gastight. Liquids are delivered at heads limited only by the power of the motor.
State Department of Geology and Mineral Industries for
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(1) Dietert. H.
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W..J . Optical Soo. Am., 31, 693-6 (1941).
(2) Frenoe.W. D.,Ibid., 32,681 (1942).
(3) H0dge.E. 5.. IND.ENO. C ~ M . , A N A L . E 14,200 D., (1942). (4) Neuhaus, C. J.. J . Optical SOC.Am., 33, 167-74 (1943). ( 5 ) Oahry, H. I., Ballsrd. J. W., and Schrenk, H. H., Ibid.,32, 672-so
(1942).
