1,
K i t h the system illustrated in Figure developing chromatograms have
been carried in vest pockets without adverse effects. LITERATURE CITED
(1) Block, R. J., Durrum, E. L., Zneig,
G., “-1 Manual of Paper Chromatography and Paper Electrophoresis,” Academic Press, Xew York, 1955. (2) Cas&, H. G., *‘Techniquesof organic Chemistry,” A. Weissberger, ed., Vol. X, p. 135, Interscience, Sew York, 1957. (3) Lederer, E., Lederer, AI, “Chromatography, A Review of Principles and
Applications,” Elsevier, Ken- York, 1957. (4) Mitchell, L. C., J . Assoc. Oflc. Agr. Chemists 40, 999 (1957). ( 5 ) Rockland, L. B , Dunn, M. S., Sczence 109, 539 (1949). APPROVEDfor publication by the director of the Wyoming Agricultural Experiment Station as Journal Paper No. 104.
Potassium Bromide Pellet Technique Alien L. Olsen, Chemistry Division, U. S. Naval Ordnance Test Station, China Lake, Calif.
used t o preN pare potassium bromide disks for solid phase infrared spectroscopy, have U J ~ E R O U SDIE DESIGNS,
been described recently (1, 3, 5 , ’79). The most practical design, from the standpoint of fabrication, produces a circular plate. To eject the pressed specimen, without damage of radial cracking or peripheral shattering, the die is provided with a split-bore chamber, or the plungers press the potassium bromide into steel rings. In the latter case, even with moderate pressing pressures, permanent distortion of thinn-alled rings occurs, restricting the number of presses available from each ring. As a n even more serious consequence, this distortion brings about a scoring of die-bore surfaces until the punches no longer pass freely. Measurement of the infrared spectra of fusible solids in a cell at elevated temperatures required a maximum diameter of the pressed halide disk. A simple, evacuable, and easily manipulated die, designed for use in the ARL-
Dietert briquetting press and eniploying a new technique of pressing the ‘/,-inch diameter pellet directly into a 1-inch diameter ring, is described. The pressed disk fits directly into the PerkinElmer demountable cell holder, or by removal of the lead ring, the disk can be inserted in the specimen holder of the high-temperature cell (6) I
APPARATUS
The various parts of the die assembly, designed and fabricated by the Applied Research Laboratories, Glendale, Calif., are shown in Figure 1. The die body was machined from a 3-inch diameter AIS1 440C stainless steel rod and hardened t o a Rockwell C-50. Tungsten carbide cylinders, Kennametal K-96, provided with a 4microinch finish on the pressing faces, become the top and bottom plungers. A 1-inch stainless steel rod serves to insert the seal ring into its O-ring groove ivithout damage and to pack initially the pondered potassium bromide into the lead ring. The filling sleeve provides a means of inTOP CAP
TUNGSTEN CARBIDE
Figure 1 . Die assembly for pressing potassium bromide disks
n -7
TAMPER O-RING GUIDE
O-RING
,/ ,-FILLING SLEEVE UPPER PLUNGER
HOSE ADAPTER
RING LOWER PLUNGER COLLAR LOWER PLUNGER
traducing the powdered potassium bromide into the die body. A constraining sleeve for the upper plunger makes it possible for the pressing surfaces to compress the powder within the lead ring. O-rings within the die body and on the under side of the top cap provide adequate seals for evacuation. Lead rings with 1-inch outside diameter, 7,’s-inch inside diameter, and a length of l/s-inch can either be machined by use of simple jigs or punched out from a sheet of alloyed lead. As the potassium bromide die is now commercially available from the Applied Research Laboratories, details on tolerances are omitted. S n BRL-Dietert briquetting press was employed in the pressing operations. A Perkin-Elmer Model 21 spectrophotometer n-as used to determine transiiiiqsion data. TECHNIQUE
Sample Preparation. For qualitative cleterminations, approximately 2 grams of infrared-quality potassium bromide, and 3 t o 5 mg. of finely divided sample n ere weighed out. The vibrator-grinding technique n as used for the dispersion of the sample in the ponder ( 5 ) . Pressing Operation. The lower plunger, attached to the top of the ram by the retaining ring, and the die are placed a t the top of the recess of the briquetting press. The ram and plunger are lowered to the bottom position and the lead ring and filling sleeve are inserted into the bole. The powder charge is introduced and leveled n i t h a straight edge of a spatula. The plunger-tamper further flattens and compacts the charge within the lead ring. The top plunger with its retainer sleeve is inserted into the die bore; the bridge of the prms is secured in pressing position, and the die cavity is evacuated for 2 minutes. 4 pressure of 80,000 pounds total force or approxiniately 133,000 p.s.i. is applied for 2 minutes. The pressure is gradually released to zero dial reading and the vacuum line is opened to the atmosphere. The bridge support is swung to the ejection position, holding the die body with one edge of the bridge, n-hile the compressed pellet is ejected by the ram action. If the lead ring adheres to the punch, a simple twist removes ring and pellet. Lead flash, VOL. 31, NO. 2, FEBRUARY 1 9 5 9
321
if it occurs. may be trimmed off with a razor blade. The lead ring may be reused. The potassium bromide pellet is pushed out, and the lead ring is inserted with a 180" orientation into the dic bore. RESULTS AND DISCUSSION
The necessity for employing high pressures in the satisfactory production of potassium bromide pellets n as early recognized in thi5 investigation. Kereiakes (4) showed by x-ray diffraction methods a decrease in the grain size of potassiuni chloride powder M ith increasing prebsures. Ingebrigtson and Smith concluded that both pressing pressures and prcssing times affect the quality of the pellet ( 3 ) . The higher pressures available from the briquetting p r e s produced a single-crystal, clear specimen which remained transparent for several weeks. Cloudy areas, a phenomenon occurring at low pressures with nonuniformity of powder distribution over the face of the die, were virtually nonexistent. In the usual technique of disk fabrication, either the die required precise machining and a high surface finish, or the material was pressed into steel rings. In the latter case, tremendous tensile stresses are set up during the pressing operation n hich bring about permanent distortion of the steel ring with attendant scoring of the die bore
during ejection. After several pressings, the ring no longer fits into the die bore. Obviously, the lead not only provides a suitable support for the disk, but also affords a type of lubrication I\ hicli virtually eliminates scoring of die-bore surfaces. Of the several designs which have been used in this a ork, one die in particular has successfully produced over 200 disks without nialfunction. Rings fabricated from unalloyed lead are readily reinserted for additional use and a single ring is capable of producing 12 to 15 pressings. For quantitative applications, some degree of tolerance of ring dimension was achieved in the punch-out process by alloying with arsenic and antimony. These less pliable rings do not reinsert easily. In quantitative applications, a new ring is used for each pressing, while for general routine FT-ork, punch-out rings from ordinary 1/8-inch thick sheet lead work satisfactorily. Potassium bromide disks pressed under the conditions mentioned earlier showed maximum transmittances of 89.5%. This value compares favorably with the measured value of 90.3% a t 2 microns for single-crystal potassium bromide. Energy losses from reflection. scattcring, and absorption amount to about 10 to 11%. The disk generally exhibits 2 to 3 7 , spread betn-ecn niiniriiuni and maximum tr ansniit t awe.
The effect of taper on absorbance measurements has been evaluated (2, I O ) . If reproducibility in transmittance becomes important, the disk is rotated to maximum transmittance prior t o the scan. ACKNOWLEDGMENT
The author desires to express his appreciation to many members of the Applied Research Laboratories, Glendale, Calif., for assisting in the developnient of this technique and for granting permission to print the line drawing of the potassium bromide die. LITERATURE CITED
(I) Anderson, D. H., Smith, R. G., A N A L . CHEM. 26. 1674 11954). (2) Browning, R.' S., hberley, S. E., Xachod, F. C., Zbzd., 27, 7 (1955). (3) Ingebrigtson, D. S . , Smith, A. L., Zt~zd.,26, IT65 (1954). (4)Kereiakes. J. G., Phiis. Rei,. 98. 553 (1955). 15) Kirkland. J. J.. ANAL.CHEX 27. 1537 ' i1955). (6) Olsen, A4.L., Ibid., 30, 155 (1958). ( 7 ) Perkin-Elmer Corp., Instrument ,+-eu,s 5 , S o . 3, 5 (1954). (8) Ryason, R., J . Opt. SOC.Am. 43, 928 (1953). (9) Scheidt, C., Reinwein, H., Z. S a h r forsch. 76, 270 (1952). (10) Spell, -4.,Rector, H. E., Pittsburgh Conference on Applied Spectroscopy and Analytical Chemistry, Pittsburgh, Pa., March 4, 1954. I
,
Plastic Diaphragm Valve for Burets Kenneth A. Allen, Oak Ridge National Laboratory, O a k Ridge, Tenn.
A
diaphragm valve for burets eliminates many of the difficulties encountercd with commercially available greaseless ~ a 1 1 . c ~Greaseless valves have considerable advantages for aqueous systems and are almost indispensable for certain nonaqueous systems -e.g., sodiuni (>thosidein benzene or perchloric acid in dioxane. Fluoroplastic plugs are difficult to fit to ordinary stopcock barrels, and tend to stick, making fine adjustments difficult. I W i glass needle valve types, liquids tend to leak past the inert' plastic around the needle and come in cont'act with the noninert plastic parts. I n addit,ion, the handles come loose. With the valve diagraninird delicate flow rate adjustments are made easily and precisely. Bubble trapping in the chamber was not a source of difficulty. The diaphragm did not set during buret storage, if the valve was left open, and the diaphragm could easily be reversed or replaced. PLASTIC
0pera.tion of the valve is apparent.
322
ANALYTICAL CHEMISTRY
The body and diaphragm are made from a resilient, inert plastic, such as Teflon
Figure 1. 1.
Diaphragm valve
Inlet and outlet tubes pressfitted into b o d y 2. Body 3. Plastic or metal retainer holds diaphragm against the b o d y with leaktight pressure 4. Diaphragm out of resilient, inert plastic 5. 'Chamber ca. 20 mils 6. Adjustor
or polyethylene. The retainer is of some stiff plastic, such as polymethacrylate or Bakelite. It could also be made of metal, because it does not come in contact nith the liquid. Turning out the body and retainer are machining jobs, but thwe are no critical tolerances. Even the chamber spacing between the diaphragm and body can be 0.020 =k 0.005 inch. ;Is long as the inner spacing between the retainer and the body is reasonably true, considerable rariation is allowable in the other dimensions. The inlet and outlet holes in the body are drilled a few mils smaller than the outside diameter of the glass tubing selected for sealing to the buret and forming the exit nozzle. The resulting press fit is satisfactory with regard to both the seal and the necessary mechanical rigidity. Suitable diaphragms can be cut from '/,,-inch sheet material with a cork borer. This automatically provides a slightly raised, sharp edge which helps make a leaktight seal against the body. Thumbscrews from standard laboratory hardware, with the ends filed smooth, make eucrllmt adjustors.
