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V O L U M E 26, NO. 9, S E P T E M B E R 1 9 5 4 Mechanical Slit Control for the Beckman IR-2 Infrared Spectrophotometer. Dean H. Couch and A. L. Sstterthwaite, U. S. Naval Ordnance Test Station, Chins. Lake, Calif.
on, so that a warm-up period is not needed for the next run. Thus, after starting the instrument no further attention is required to complete the recording.
slit control for the Beckman IR-2 infrared with it the infrared absorption spectra. of compounds can be recorded directly in per cent transmittance. Blanks are recorded st 100 =t 5% transmittance. Beckman IR-2 infrared spectrophotometers have been in use for several years, and several mechanical slit controls have been developed. Some of these devices consisted of a simple spool and belt arrangement ( 1 , 2). Another type of slit control, essentially the same BS that described here, has been used by the California Research Carp. for aeverd years (S). The design considerations and the procedure for collecting data have been discussed by Tolberg and Boyd (4). The conversion of the data to information necessary for the construction of the control differs from that of Tolherg and Boyd in that an approximation method was used.
RESULTS AND CONCLUSIONS
MECHANICAL
A spectrophotometer has been devised;
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This slit control gives a blank recording a t 100 5 % transmittanoe between 2.5 and 15 microns. For recording the blank, the gain control w u set on 10 and the variable control was set a t 627' of maximum. The carbon dioxide and water vapor hands artre alwaytys recorded.
CONSTRUCTION OF SLIT CONTROL
A plot of diameter us. revolutions for the spiral was made for the machinist. The spiral was made of brass plates 0.25 inch thick, which were bolted together as they were milled to shape. The coue-shilped drive spool w m made from solid brass. The final working model of the slit control iS shown in Figure 1, in operating position on the Beckman IR-2 infrared spectrophotometer. A No. 3o piano wire is used to link the spool and spiral together. Other modifications which add to the convenience of operation of the spectrophotometer are presented in Figure 2. OPERATION O F SLIT CONTROL
The instrument is turned on and allowed to warm up as usual. The starting conditions for the slit control are cheoked by turning the wavelength drive knob to the 2.50-micron position. The Nave-length drive clutch is engaged to hold this position. A mark on the bottom edge of the drive spool should line u with a mark on the frame below it, A similar mark on the spira7should line up with a vire on the left side of the frame, After these points are checked, the slit is adjusted to 0.880 revolution, and the Jacobs chuck is tight,ened. The wave-length drive clutch is apened and the device is turned hack manually to 15 microns.
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Figure 2. Wiring Diagram Operating tests have shown this slit control is satisfactory for genera1 studies of infrared absorption spectra. It produces per cent transmittance recordings that are easily compared in contrast to the difficulties encountered with the original sawtooth type recordings. The Slit control has been in use since January 1952. No appreciable change in the blank recording has resulted from changes in the glower, sensitivity of the thermocouple, 07 other variables. LITERATURE CITED
(1) Badger, R. M., California Institute of Technology, private com-
munication.
(2) Beach,
J. Y . , paper presented at Ohio State Symposium on Moleeulsr Structure and Spectroscopy, Columbus, Ohio, June 1951. IRI Rhreve. 0.D.. and Henther. M. R.. ANAL. C ~ E M .22, . 835-7
Paper Ionograms. H. L. Demorest and Richard Baskin, Radioisotope Unit, Veterans Administration Hospital, Minneapolis, Minn. NEED
has arisen in this labomtory for a sensitive detector
A to be used for paper chromatogram and paper ionogram
Figure 1. Mechanical Slit Control for the Bediman IR-2 Infrared Suectrouhotorneter
The recorder is standardized and the zero position is checked. The recording is started by engaging the wave-length drive clutch. Tlihen the wave-length scale reaches 9 microns, a knot on the load cord tips a mercury switch and closes a solenoid (Figure2). This changes the rotating shutter from glass to metal. A t the end of the run the load weight is drawn up against a limit switch. This shuts off the wave-length drive motor, recorder motor, and solenoid. The rest of t.he electronic equipment is left
scanning in which the compounds are tagged with carbon-14, a weak beta emitter. T o date, the position of the compound tagged with carbon-14 has been located on the filter paper by moving i t heneath a thin-window Geiger counter [Frierson, TT-. D., and Jones, J. TV., ANAL. CHEM.,23, 1447 (1951)l ionization chamber [Jones, A. R., AN&[.. CHEM., 24, 1055 (195211, or by cutting the filt.er pnper into small sections which are then counted in a proportional counter. I n order to he able to improve the sensitivity of detection over the thin-window Geiger counter method and to avoid the tedious procedure of cutting the filter . Dmer . into sections. an instrument has been developed in which the sample is placed within the counting chamber of a gas How counter. The paper is then scanned within the chamber for the presence of radioacti INSTRUMI
As shown in Figure 1, the ...l... _.I_____._ a chsmher housing, D,with a slotted plate, H,a main chamber I_
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