Scribner, B. F., “Spectroscopy in Science and Industry,” p. 52, New York, John Wiley & Sons, 1938. Torok, Tibor, Spectrochim. Acta, 2, 300 (1943).
Combined Shutter and Projection Device for Alignment of Electrodes in Spectrographic Analysis. A. Lee Smith and V. A. Fassel, Institute for Atomic Research and Department of Chemistry, Iowa State College, Ames, Iowa.
P.APER13 of t h e Institute for Atomic Research. Work done under Contract W-7405 eng-82, M a n h a t t a n District, U. S. Corps of Engineers. F. H. Spedding, project director.
spectrographic analysis the position and spacI ingquantitative of the electrodes are critical if reproducible results are to 11’
A Colorimeter Tube Adapter for the Pfaltz and Bauer Fluorophotometer, Model B. Richard L. Durst and John B. Lewis, S. F. Durst & Company, Inc., Philadelphia 20, Pa.
be obtained. Proper alignment is usually made by means of an auxiliary lens which projects the electrode image on a previously marked screen (2, 4 ) . In some cases the electrodes are quickly positioned after the exposure has been started; for more careful work, the electrodes are aligned before excitation by the use of B manually operated lamp or projection device placed behind the electrodes t o project their image (1, 3, 5 ) . The apparatus is almost instantaneous in action and is operated electrically by conveniently placed push buttons. It also provides an excellent shutter for spectrographs not already so equipped. It operates on the principle that an iron rod placed in a solenoid tends to center itself when alternating or direct current is passed through the windings.
INreadings several colorimetric methods used in the control laboratorv are best made in reaction tubes, to avoid transfer
and time losses. With commercial equipment the authors found randcm variations of considerable magnitude, and it was observed that the taller the chemist the smaller the variation. This was found to be due to variations in diffused light that was reaching the instrument from windows behind the operator. When the colorimeter tubes were wrapped with black tape for 5 cm. (2 inches) above the chamber of the instrument, practically all variations were removed. The device illustrated has been used with excellent results. The construction and dimensions are self-evident. A drawn copper tube could have been used but would not have been as satisfactory as the heavier machined tube, which more firmly seats the unit in the cuvette housing. This adapter was made to fit No. 9800 Pyrex tubes 18 X 150 mm., with as little wobble as possible. The adapter furnished by the company as an insert for the cell carrier‘was found to be unnecessary with well-fitted tubes. Colorimeter tubes were obtained by selecting from several dozen tubes those which fitted the adapter, and classifying them for transmittance into groups of reasonable identity with various filters. The green trade mark is used as the position marker when reading.
I The assembly is mounted on a 0.125-inch brass plate bolted to an optical bench carriage. The double solenoid is made by winding enough KO. 32 cotton-covered copper wire on a 4-inch brass tube with Bakelite spacers to give a resistance of about 80 ohms in each section. The soft iron core, 4 inches long and 0.25 inch in diameter, should slide freely in the tube. The polished steel mirror is mounted on an arm which is free to rotate through . a 45” angle, thus swinging the mirror in and out of the optical path as the position of the solenoid core changes. A spring bears against the notched disk which is a part of the mirror arm, and ensures the mirror’s stopping in the same position each time. A metal stop near the edge of the base plate limits the motion of the mirror. If desired, a circuit contact may be mounted on the mirror arm to turn on the lamp automatically when the mirror is in the projection position. The lamp used on the instrument described is a 50-watt toy projector bulb of type S-11, although any similar lamp may be used. The socket is mounted on an insulated platform which is fastened to the base plate. A cover may be placed over the whole assembly, with suitable holes cut for the optical path. Electrical connections may be made by means of a tube socket mounted back of the lamp. The two sides of the double solenoid are activated by individual push-button switches (momentary contact) mounted in a convenient place.
-2.9
3.72”4
ACKNOWLEDGMENT
The plate was constructed by riveting together two pieces of brass sheet and boring and threading a hole through them. The tube was made by boring a piece of 2.5-cm. (1-inch) brass rod and threading one end to fit the hole. This device was made by the George B. Henne Company, Philadelphia. To avoid internal reflections the surfaces were blackened (by Plummer and Kershaw, Philadelphia), with optical black, which produces a dull finish integral with the metal.
The authors wish t o thank Lael Smith for assistance in the const uction of the instrument. LITERATURE CITED
(1) Applied Research Laboratories, Catalog 128, p. 17. (2) Brode, W. R., “Chemical Spectroscopy,” 2nd ed., p. 55, New York, John Wiley &Sons,1943. (3) Clayton, H. R.,J.Sci. Instruments, 18,65 (1941).
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