Salvaging of Silver Chloride Windows Worren C. Schwemer, John E. Murphy, and l e e Williamson, Research and Development Division, S. C. Johnson & Son, Inc., Racine, Wis.
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silver chloride windows used in infrared spectroscopy [Fuoss, R. M., Rev. Sei. Instr. 16, 154-5 (1945)) usually have a short life expectancy, as they are easily scratched and darken on exposure to light. These sil3er chloride windows, being insoluble in water, make possible the determination of the infrared spectra of wax and polymer films deposited on the silver chloride windows from water emulsions. A technique has been developed which restores these silver chloride plates to their original transparency and thus lengthens their life expectancy severalfold (Figure 1). The change in the absorbance of the silver chloride disk before and after treatment is shown in Figure 2. OSTLY
Pittsburgh Conference and the Anilysl
Figure 1.
coarseness. The window is then immersed in concentrated ammonium hydroxide for about 2 minutes, rinsed with water, and rnhhed dry with a lintless cloth. This ammonia treatment removes any layer of reduced silver which may have been present on the surface of the window [Giesecke, P., Colthup, N. B. (to American Cyanamid Co.), U. S. Patent 2,528,224 (Oct. 31, 1950)l. To remove the surface scratches from the windows, advantage is taken of the fact that silver chloride will flow under pressure. The windows are placed in a polished, chrome-surfaced die, l'/s inches in diameter, and pressed at a pressure of 8000 pounds per square inch. The die used for this purpose is a Carver test cylinder (Figure 3), the faces of which have been ground, lapped, and chrome-plated. The press used was a Carver laboratory press which was purchased for use in forming potassium bromide pellets. For use in PerkinElmer cells the pressed windows are trimmed with a 1-inch-diameter punch.
Silver chloride windows Leff. Dornoged Right. Salvaged
To restore these silver chloride disks to their original transparency, surface scratches and foreign material which may have reacted with the silver chloride must be removed. The foreign material is first removed from the silver chloride by scraping the surface of the window with a single-edge razor blade and sanding with No. 600-A wet-dry sandpaper or other paper of similar
Figure 3. Die used for removing scratches from silver chloride window
Bulb Tube Assembly for Vacuum Distillation Anthony W. Schrecker, Laboratory of Chemical Pharmocology, National Cancer Institute, Nationol Institutes of Health, Public Health Service, Bethesda
14, Md.
described is a modiT fication . of Kober's bulb tube [S. HE APP.%RATUS
Kober, Biochem. Z. 232, 274 (1931)], which has been used extensively for vacuum distillation and sublimation of small quantities. In its original form, it consists of three or more bulbs fused together by pieces of glass tubing. Figure 1 shows the design of the assembly. The bulbs, which may be constrncted from borosilicate glass round-bottomed flasks, are connected by means of B 14/35 standard-taper drip-tip ground joints (for which 14/20 joints could be substituted advantageously). Adapter D connects the assembly with the vacuum system hy rubber tubing. In operation, the distilland, dissolved if necessary in a solvent, is introduced into flask A . The solvent is evaporated in vacuo, most conveniently by use of a rotating evaporator (Rinco Instrument Co., Greenville, Ill.), to which the flask is attached by means of an enlarging adapter (19/38 outer, 14/35 inner joint). Parts A, B, C, and D are then assembled in series, clamped horizontally, and flask A and the adjoining length of tubing are inserted into a heating oven (FigureT2), so that bulb B iust Drotrudes. Tube D is attached to the Gacuum system, and the oven heated gradually. The distillate collects in B. By further inserting the assembly so that only bulb C protrudes from the oven, part or all of the material can be redistilled and some fractionation accomplished. The heating oven consists of a Transite box enclGed in an aluminum shell, 32 X 14 X 14 em., the space in between the two filled with rock wool. The
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Figure 2.
. I _ I mw "m.," c * m Infrared spectra of silver chloride window before (bottom) and after (top) treatment
VOL 29. NO. 7, JULY 1957
11 13
Fiaure 1. Vacu" um-distillation assembly
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This assenibly presents certain advantages over Xober's original tube. With the old design, it was difficult to evaporate the solvent without contaminating the second bulb with droplets of the distilland. Recovery of the distillate without contamination was also difficult, as it was necessary to cut the glass tubing between the bulbs. Accurate determination of yields is also simpler with the new design. Transfer of the distillate into another flask becomes an easy matter. The drip-tip joints and the direction in which they are arranged prevent contamination of the distillate by vacuum grease (Dow Corning high vacuum silicone grease, stable to over 200' C., is suitahle for lubricating the joints). The apparatus is equally suitable for vacuum sublimation. The diameters of the bulbs may he varied to accommodate larger or smaller samples and, by reducing the length of tubing, a larger number of bulb unite may be used. By attaching appropriate standard-taper condensers or condensation traps in that part of the assembly outside of the oven, materiak of high vapor pressure may be vacuum-distilled and collected.
The author is indebted to Frederick Highhouse, NIH Instrument Section, for advice in designing this assembly. The heating oven was designed by Grant C. Riggle, NIH Instrument Section, and by Ronald B. Ross of this laboratory in modification of a design kindly supplied by R. K. F. hlanske.
Robert E. Davis and J. M. McCrea, Petroleum ond Chemical Research Loboratory, The M. W. Kellogg Co., Jersey City,
introduction is an important S factor influencing precision of gas chromatographic analyses (8). The AMPLE
system developed in the writers' laboratory permits rapid introduction of small, reproducible volumes of liquid samples into a gas chromatographic column. It is an adaptation of a standard mass spectrometer liquid inlet system to gas chromatography, and
common method of injecting liquid samples with a hypodermic or micrometer syringe and serum bottle cap was introduced by Ray ( 5 ) , hut is difficult to control for small samples and results in an effective sample chamber of indefinite volume. A special needlesyringe device developed by Adams ( I ) allows introduction of controlled small volumes, but is rather difficult to manipulate and necessitates venting the column before injecting samples. More elaborate systems for sample introduction, utiliiing bypass systems with a bellows crusher (3) or cold trap ($I), involve time-consuming operations and hence are unsuitable for routine use. Bypass systems are desirable, however, as they permit introduction of the sample in a reproducible manner (8). A bypass-type liquid sample inlet 1 1 14
ANALYllCAL CHEMISTRY
STOPCOCK POSITIONS
'6
N.J.
utilizes an evacuated ehamber with mercury - sealed orifice, appropriate means for bypassing and sweeping out the sample chamber with carrier gas, and capillary pipets for measuring and transferring the liquid samples. The system is readily adaptable to most
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