ANALYTICAL CHEMISTRY
2022
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Small flashes and explosions will probably occur at the junction of the side arm and the platinum gauze section; these explosions are controlled by pinching the rubber tube from the Niederl gasometer or the leveling bulb. The silicon-hydrogen bonds will be broken by the hot platinum catalyst. Organic compounds may reach the copper oxide catalyst, but will be oxidized there. Halides, if present, are trapped on the hot silver catalyst. The amount of sample to be burned should be governed by the appearance of the indicating Drierite. This method has given good results with gases containing silane, SiH,, and ethylsilane, C2HjSiH3. Sample CHIC1 9j%ClHsSiHr
61Hb
4-5% Nz
Theoretical C, % H, 7% 23.8 6.0 38.0 12.7 0 12.6
Determined C, % H, % 23.4 6.0 37.7 12.6 0 12.6
LITERATURE CITED
(1) Brunn, J. H., and Faulconer, W. B. RI., IND.ESG.CHEM.,ANAL. ED.,8,315-16 (1936). (2) Niederl, J. B., and Niederl, Victor, "Organic Quantitative Microanalysis," 2nd ed., pp. 101 et seq., Wiley, New York, 1942. (3) Pregl, Fritz, "Quantitative Organic Microanalysis," revised and edited by Julius Grant, 4th English ed., pp. 33 et seq., Blakiston, Philadelphia, 1946. (4) Zimmerman, Wilhelm (to I. G. Farbenindustrie A.-G.\, Ger. Patent 642,166 (Dec. 1, 1934).
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Infrared Capillary Cell for Volatile liquids Raymond H. Pierson and Allen L. Olsen, U. S. N a v a l Ordnance Test Station, China Lake, Calif.
-5mm 5mm-
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FRONT VIEW OF SALT WINDOWS
the production of infrared spectra, a capillary cell is someF times preferred to a fixed space cell, because the capillary provides a thinner sample film and is easier to recondition if
Figure 1
the salt M-indows become contaminated. A problem arises in using the capillary cell if the sample is volatile. Two simple modifications for overcoming this difficulty utilize reservoirs to provide replacement of material lost through volatilization a t the edges of the salt windows, and are, therefore, applicable only to single component liquids and to qualitative work. Many workers (1-6) hsve proposed designs of infrared cells for handling volatile liquids. While the present suggestion offers only a partial solution to the general problem, it describes apparatus that can be made in a very short time from inexpensive and readily available materials using simple tools. The simplest modification is accomplished by making a small depression in the salt windows themselves, as shown in the lower portion of Figure 1. (The Teflon and glass pieces are not utilized in this simplest modification.) Two salt plates held in a demountable cell frame are drilled a t moderate speed either with a steel drill or with a spherical burring tool (rotary file). By using the latter tool a hemispherical depression is produced instead of the cylindrical one shown in the figure. X hypodermic syringe and needle are used to fill the cell and to keep the reservoir filled during production of a spectrum. -4little loosening and retightening of the frame may occasionally be necessary for the eliniination of air bubbles on first filling of the cell. For a moderately volatile liquid such as ethyl alcohol, less than 1ml. of liquid will be required during a determination. The cell can be used with or without a spacer. When no spacer is used and it is desired to determine the average sample thickness, the capillary is best calibrated by measuring peaks of a suitable solvent in the capillary cell and in several fixed cells.or a variable-space cell and calculating the capillary space from a plot of thickness against absorption. The cell described is not suitable for more volatile substances such aa carbon disulfide or acetone. A modification employing a Teflon and glass insert has been found adequate for these liquids and is also illustrated in Figure 1. Because the normal operating temperature a t the cell is about 37" to 39' C.,even this second
modification is not suitable for liquids (such as ethyl ether) which have boiling points below 40' C. Although drilling is done in the vertical position, the windows are rotated in use, so that the reservoir is a t about 10 o'clock. In this position there is an adequate slope for gravity feed of the sample, but the drill hole and insert are outside the path of the infrared beam. The Teflon portion of the insert is made by drilling a plug commonly furnished for closing Perltin-Elmer fixed cells. Drill sizes as indicated in the figure were found suitable but are not critical so long as reasonably snug fits are obtained. Teflon may be undesirable for some liquids, but otherwise its use as an adapter for the glass tube is advantageous (because of the softness and cold-flow properties of Teflon) over a direct glass-to-salt window connection. The total reservoir capacity of the cell shown is about 0.3 ml. For a 40-minute spectrum trace a total of five fillings (1.5 ml.) were required with carbon disulfide and one and one half fillings (about 0.5 ml.) with acetone. When reasonable care is taken in keeping the capillary filled during spectrum tracing, there should be no dripping of solvent onto the base of the instrument. Possibility of accidental solvent damage to the instrument finish may be guarded against in a number of ways-for example, by arranging several layers of cloth so as to intercept any spillage or droplets. If highly flammable liquids are examined in the cell, suitable precautions should be taken regarding fire or explosion hazards.
OR
LITERATURE CITED
(1) Broadley, H. R., Rev. Sci. Instr., 19, 475 (1948). (2) Friedel, R. il. and , Pelipets, 11.G., J . Opt. Soc. Amer., 43, 1051
(1953). (3) Fry, D. L., Nusbaum, R. E., and Randall, H. hi., J . A p p l . Phys., 17, 150 (1946). (4) Oetjen, R. A., Ward, W. hl., and Robinson, J. A., J . Opt. Soe. Amer., 36, 615 (1946). (5) Smith, D. C., and Miller, E. C., J . Opt. SOC.Amer., 34, 130 (1944). (6) Smith, F. -4., and Creits, E. C., d s . 4 ~ .CHEM.,21, 1474 (1949). >
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