Karl Fischer Titration Aid. J. B. Xhittum, R. F. Goodrich Chemical Co., Niagara Falls, N. T.
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HEX use of t,he Karl Fischer reagent was recently started in this laboratory, considerable difficult'y was experienced \wc:tuse even t r a i n 4 operators had some trouble seeing the end point, using comparison samples :ind stopping dropwise to compare the color of the solution t o a standard. During titration the yellow solution gets gradually darker, tending t.owards i i light orange which is very difficult to see with precision. Thr, trouble experienced with this difficult) end point prompted a search for an easier and more accurzite one. Potentiometric titratiori has been used elsem-here with success, hut involves espensive equipment (Mitchell, John, Jr., and Smith, D. AT., '..-\quametry," N e y York, Interscimcc Publishers, 1948).
Inexperienced operators can be quickly trained to obtain accurate results with the colored lights in less time than an experienced operator using whit>e light, and tit,rating time is reduced even for an experienced operator. When large amounts of water are tit,rat'ed, the background color interferes somewhat,, so that the end point is obscured as under t>hewhite light. Even under these conditions, however, the yellow light titration is easier. Because of this background interference, the described method shows the greatest advantage when small amounts of water are titratrd with greater precision than is normally attained with larger amounts of water. The methyl orange and methyl red end points are also more tmily seen under the yellow light. In other titrations with difficult end points, lights of an appropriatc color might well be of value. TWOgold-colored, I h r a t t , fluorescent lights are mounted in a light box with t,he Karl Fischer buret (see diagram). Although the app:u:ttus is shown with the particular buret used in this Ittbolatory, minor modifications would adapt it t o ot,her equipnicnt. The yellow color is predominant in the box and by transniission makes the titrated solution apprar colorless initially iristrad of yellow. The eiitl point is nluch more readily seen. I t is important that most of the white light from the room I)e excluded from the titration box. 111 a laboratory where sewral tlific~ri~rit types of titrations are done, it is convenient to provicic, :i titration booth or room with both yellon- and white lighting. Improved Cutting Tool for Spectroscopic Electrodes. Alfred T. 31yrrs1, I-. S. Geological Survey, Washington 25, D. C. v iiiiprovrsd shaping tool has been developed as the result of
A'sewral years of
.46" FLOOQ
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It is ivell known that a colored solution transmits a mavimuni oi light of the same color as the solution. A colorless solution transmits substantially all the light that falls upon it. The human eye is so adaptable that under a colored light a solution which transmits all the incident light (or an equal percentage of all incident wave lengths) appears colorless. By an analogous phenomenon, a material which reflects all the incident light appears to be white (Evans, R. M., "Introduction to Color," Ken- York, John Wiley & Sons, 1948). If the Karl Fischer titration, therefore, is carried out under a yellow light, the original yellow solution appears colorless. The end point, now a bloody pink, can be detected much more precisely. Although the increased precision is probably not equal to that attainable with potentiometric methods, it is considerably higher than normal and the equipment is much less costly.
experience in cutting elechode cavities whrw wnie of the outside will is r t ~ r n o w d . The final result is a greatly improved version of H tool first tlrscrit)ed by Myers and Hrunst,?tter ( 1 2 ) . Others have described devices for cutting graphite electrodes used for spectroscopic analysis ( f - f l ) IS, I'$), but the tool here described has drfinite advantages in design. I t is simple to operate and adjust, and the cavity shape can easily be changed. Its use in a lat,he makes possible the machining of cavities with a thin nall. The simplicity of design mnkcs the tool economical to build and maintain. It,has proved rxpwixlly useful where a large numhcr of elertrodes are required for handling both routine and rese:irc.h problems in a geochemical laboratory. Figure 1 shows the essential parts of the tool. Views A , B , arid C show the hollow-mill frame, C, n hich is designed to contain t,he other tool parts. The outside cutter bits, dl and do: for t,urning the outside wall, are preferably made of high-speed tool st,eel (Rex or equivalent) and are sharpened t'o cut a i t h a rounded edge instead of a point. The bits are held in place in the hollow-mill frame by setscrew SI. The type of drills used for drilling the cavities is shown in view E and designated as a, and a?. uL gives a cavity shape prFferred for making many routine analyses of rock powders. alis designed to machine cavities with flat, bottoms, whereas a2 drills cavities with bottoms the shape of truncated cones. Drills of any desired shape may be used, arid the diameter can be varied within the limits 3/22 to l / g inch. The drill shank that fits in the counterbore pilot hole is always 3/32 inch in diameter. An important part of the tool, the counterbore cutter, is shown in view D and designated as D in the other views. I t faces the top of the cavity wall and holds the drills tight in position in the pilot hole by means of setscrew. Sa. The counterbore cutter is in turn held tight in the hollo~v-millframe by setscrew S1. The size
' Present address, Trace Elements Laboratory, Denver Federal Center. Denver 14,Colo. 209
210
ANALYTICAL CHEMISTRY
of the counterbore is important. The outside diameter of the cutter should be l1/81 inch, and the pilot hole should be 3/32 inch. The tool is used in the headstock of a small bench lathe in the survey laboratory, but it can be used in a small portable shaping
This tool has also been used to make cavities for the pedestal type of electrode described by Scribner and Mullin (14). When undercut cavities are desired, the graphite rods are held in a collet in the lathe headstock, Lvhile the tool is held in the tailstock. Af-
HOLLOW-MILL
FRAME
SUSJECT '#I-H , , C"ERCTICr\S
COMPLETED
STS. 3 FLUTED &CIA. CO-BORE WITH REMOVABLE P I L O T PILOT HOLE C I A . &
INTERCHANGEABLE PILOT CUTTERS
PILOT CUTTER
( H E A D SHdPE TO BE SPEC1FIED BY DESIGNER)
CO-BORE TOOL
CROSS SECTION "ARTS AS3EMBLED
EXPOSING
F i g u r e 1.
G r a p h i t e C u t t i n g Tools
lathe of the type described by Majors and Hopper (IO), or in a drill press, if a suitable device for holding graphite electrodes is available. The tool i s enclosed in a Lucite box to protect the user and to confine the carbon dust, which settles out on a tray a t the bottom. Advantages. All the cutting parts are made of high-speed tool steel, which stays sharp a long time. The drills are made of high carbon steel. All cutting parts are easily sharpened with a small Alundum stone. The outside cutters allow cutting of thin walls; walls of any desired thickness may be produced by different settings of these outside cutters. This is in line with recent trends toward using more uniform electrode cavities in order to obtain greater reproducibility in the direct current arc. Drills may be designed to cut out any desired cavity geometry. These drills are not difficult to make, and they are interchangeable for any tool made, as long as the same standard size counterbore is used. Different cavity depths are easily obtained by sliding drills a1 and a2 in or out of the pilot hole. Hampton and Campbell (6) used an electrode with a coneshaped cavity. K. J. Murata working in the survey laboratory used a similar cavity but left a small flat floor a t the bottom in the shape of an inverted truncated cone (see drill at). This shape is shown cut on an electrode, e in Figure 1, view B. This flat floor prevents residual beads of refractory elements like zirconium, columbium, tantalum, platinum, and tungsten, from becoming lodged in a pit a t the end of the burning. The counterbore cutter, D, can be obtained from a manufacturer of twist drills and counterbores for as little as $2.90. Its availability simplifies design problems, and makes the tool very flexible because many kinds of drills may be utilized in machining cavities. Different drills of the proper diameter and shape will cut cavities on l/g-, ' / 1 6 - , I/*-, or 6/16-inch graphite electrodes. It is convenient to have three of these tools on hand. Two are used for cutting a cavity of the type found most useful in routine work, ensuring a steady production of these electrodes. The other tool is reserved for making cavities of unusual shapes for special problems.
ter the caviti is machined it can easily be undercut with a too1 at a fixed distance below the cavity end. ACKNOWLEDGMENT
The miter wishes to thank K. J. Murata and J. L. Ramisch of the Geological Survey, U. S. Department of the Interior, R. IT. Davis of the Bureau of AlnimalIndustry, and J. F. Mullins of the Bureau of Plant Industry, U. S. Department of Agriculture, for advice and valuable suggestions that made the design of this tool possible. LITERATURE CITED (1) Applied Research Laboratories, Glendale, Calif., motor-driven electrode cutter and saw No. 2380, "-4.R.L. Spectrochemical Equipment Catalog," 1941. (2) Bausch 8; Lomb Optical Co., Rochester, ?;. Y . ,electrode shaper No. 33-84-09, "Bausch & Lomb Spectrographic Accessories Catalog D-220," p. 4 (1948). (3) Churchill, J. R., IND.ENG.CHEM.,ANAL.ED.,17, 66 (1945). Am., 34, 621 (1944). (4) Eastmond, E. J., J . Optical SOC. (5) Goldspiel, S., and Levine, H., SOC.Applied Spectroscopy, Bull., 4 , 9 (November 1949). (6) Hampton, R. R., and Campbell, H. N., J. Optical Sac. Am., 34, 12-20 (1944). (7) Hodge, E. S., IND. ENG.CHEM.,ANAL.ED.,14,260 (1942). (8) Jarrell-Ash Co., Boston, Mass., Jaco carbon or graphite electrode driller; supplies for spectrochemical laboratory, Catalog, March 1943 (9) Keirs, R. J., and Englis, D . T., IND.ENG.CHEM.,ANAL.ED.,12, 275-6 (1940). (10) Majors, K. R., and Hopper, T. H., Ibid., 13, 647-8 (1941). (11) hlitchell, R. L., Commonwealth Bureau Soil Science, Tech. Commun. 44, 62 (1948). (12) Myers, A. T., and Brunstetter, B. C., IKD.ENG.CHEM.,ANAL. ED.,11, 218-19 (1939). (13) Oshrv, H. I., Ballard, J. TT.. and Schrenk. H. H., J. Optical SOC. A h . , 32, 672 (1942). (14) Scribner, B. F.. and hlullin, H. R., J . Research Natl. Bur. Standards, 37, 379-89 (1946) PUBLISHED b y permission of the director, U. S. Geological Survey. Presented before the Pittsburgh conference on Analytical Chemistry a n d Applied Spectroscopy, February 15 t o 17, 1950.
