holder removed and inserted in the spectrometer light path. The pressing head is automatically retracted into the die body by the plunger-body washers. The O-ring is retained in the bottom of the body and prevents damage to the plunger pressing surface when the body is placed in an upright position. After use the windows may be easily removed from the re-usable holders or the window and holder may be stored for reference. Useful Features. The die is readily constructed of inexpensive materials, requiring only moderate shop facilities. The size and shape of the window may easily be varied. The minimum number of parts, all of which are keyed, permit rapid and consistent assembly, yielding uniform windom. The pressing head and pressing base are readily cleaned and repolished. The vacuum line is open to the sample until the pressing head actually molds the window. The sample is well removed from the termination of the vacuum line. The windows are pressed and utilized in individual holders. This ease of handling facilitates window removal
from the die and proper placement in the spectrometer, because it obviates breakage or scarring from the use of tweezers. The window holders are re-usable after breaking or dissolving out the window. The windows are formed very rapidly, Windows are held in uniform and repeatable position in the spectrometer. The windows obtained from this die are consistently clear. The window described is 0.18 sq. inch. and provides a window thickness of 0.37 mm. per 100 ing. of potassium bromide-sample mixture. Mixture weights between 100 and 300 mg. are optimum. This size was designed for routine work utilizing 1 to 3 mg. of sample. However, the window width could be substantially reduced nithout loss of energy into the spectrometer, which would permit evaluation of microgram sample weights. A Carver press is normally employed a t a total load between 14,000 and 20,000 pounds on a 1.77-inch ram. Although the area of the windon- is about 0.18 sq. inch, the force on the sample is somewhat less and undefined than the total applied, because a portion of the total
pressure is used in holding the body in absolute contact with the base. This die has been in frequent use for several years, being applied to routine applications for both research and instructional purposes by numerous individuals. It has proved to be sturdy, convenient, capable of producing consistently clear windows, and eminently satisfactory. The windows retain their clarity for several weeks when properly stored. The presence of impurities in commercially available potassium bromide and surface reflections suggests the use of blank windows in the reference beam. The resulting 100% line shows no variation. ACKNO WLEDGMENl
The die described was constructed under the direction of Clemens Schoenebeck, foreman, Mineral Industries Shop, The Pennsylvania State University. COKTRIBUTION 57-37 from The College of Mineral Industries, The Pennsylvania State University, University Park, Pa. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, March 2 , 1956.
Preparation of Micro Nujol Mulls for Infrared Analysis L. J. Lohr and R. J. Kaier, Eastern Laboratory, Explosives Department, E. I. du Pont de Nemours & Co., Gibbstown, N. J.
infrared sppctra of many solid and semisolid materials are obtained from K'ujol mulls (Plough Inc., Sew York, E. Y.). AIulls are usually prepared by vibrating about 50 mg. of sample and stveral drops of Nujol in a standard Kig-L-Bug (Vodel SA, Crescent Dental hIanufacturing Co., Chicago 23, Ill.) capsule ( 5 / 8 inch in diameter and 11/4 inchcs long) containing three stainless steel balls (0.125 inch in diameter). If a vibrator is not available, the sample having the proper particle size and the Kujol are ground together intimately in ail agate mortar. Part of the Kujol containing the finely dispersed sample is scraped from the sides of the capsule 01 the mortar and is pressed betneen salt platc. The salt plates are placed in the bainplc beam of the spectrophotometer. Onlj a m a l l pwt of the Kujol and samplc is uqed in ohtaining the spectrum. The remainder of sample mixed with the Sujol adhering to the sides of the capsule and +el balls or the mortar and pectle is not eaiily recovered. Frequently, coiiqidcrable sample and S u jol arc lost during vihiation because of the loose-fitting top of the vibrator capsule. $nother disadvantage of this mulling technique i. that frequently insuffic i m t sample is ayailahle. Although the potassium bromide pcllet method reYE
1
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o
4375" DIAM
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n
.
\. Figure 1 .
CURVATURE SAME AS STfihDkRD CAPSULE
Stainless steel microcapsule
quires only about 1 nig. of sample and special microtechniques have been developed for microgram samples, it is often preferable to obtain a spectrum from a Kujol mull rather than from a potassium bromide pellet (1-3). The stainless steel ( S o . 304) microcapsule shown in Figure 1 was designed for the preparation of mulls using only 3 to 5 mg. of sample. The technique of preparing microinulls is the same as the method described above, escept that smaller quantities of sample and Kujol are needed. The microcapsule and the standard Wig-L-Bug capsule have identical external dimensions and fit into the stand-
ard Wig-L-Bug holder. The curvature of the ends of the cavity of the microcapsule is machined so that a single, stainless steel ball will thoroughly crush the sample against the ends of the cavity. The spectral resolution obtained by this micromulling technique was equivalent to or better than the spectral resolution obtained by the usual mulling method. KOunusual clumping of the sample or caking a t the ends of the microcapsule was experienced. Only a part of the mull is needed for the spectrum and most of the sample mixed with the Nujol can be recovered from the microcapsule and the salt plates. Several microcapsules which have been used for six months for preparing mulls of a nide variety of materials sholy no corrosion or w a r . ACKNOWLEDGMENT
The authors thank J . L. Hadfield for evaluation of this microcapsule. LITERATURE CITED
(1) Bak, B., Christensen, D., Acta Chem. S c a d . 10,692-4 (1956). ( 2 ) Barker, S. A., et al., Chem. & Ind. (London) 16, 318 (1956). ( 3 ) Stewart, J. E., J . Chein. Phys. 26, 248-54 (1957). VOL. 32, NO. 2, FEBRUARY 1960
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