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INDUSTRIAL AND ENGINEERING CHEMISTRY
9. The sensitivity (roughly 0.05 microgram of uranium) waa checked and found to be in good agreement with previous reports. This figure may be considered the practical sensitivity for direct application of the test to uranium minerals low in rare earths and other interfering elements. 10. A preliminary study of the chemistry involved in the test indicated that a solution of uranium in sodium fluoride is formed at any temperature above the fusion point of sodium fluoride, and that this solution on crystallization becomes fluorescent. At low flame temperatures any excess uranium remains undissolved, whereas a t higher temperatures the excess is converted to what appears to be sodium uranate which tends to quench the fluorescent phase. 11. The test, coupled with simple examination of the fluorescence spectra, afforded positive evidence that the greenish fluorescence of certain semiopals, moss agates, and hyalites is due to included uranyl compounds. 12. It is concluded that this bead test merits a place among the very few reasonably specific and reliable fluorescence tests known. It compares favorably in these respects with ordinary
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microchemical tests in general and is vastly superior to the standard ones for uranium. LITERATURE CITED
(1) Goddard, E. N., and Glass, J. J., Am. Mineral., 25, 381-404 (1940). (2) Hernegger, F.,Anz. Akad. Wisa. Wien Math. naturw. Klaase, No.2 , 15 (1933). (3) Hernegger, F.,and Ksrlik, B., Sitzber. Akad. Wisa. Wien Math. naturw. Klasse, Abt. 2A,144,217-23 (1935). (4) Hoffmann, J., Spreehsaal, 73, 153-7 (1940); Chem. Zentr., I, 3963 (1940). (5) Hoffmann, J., SprechsauZ, 74, 155-7 (1941); Chem. Zentr., 11, 642 (1941). (6) Lee, 0 . I . , Chem. Reviews, 5 , 17-37 (1928). (7) Lee, 0.I., personal communication. (8) Nichols, E. L.,and Howes, H. L.,J. Optical Soc. Am., 13,573-87 (1926). (9) Nichols, E.L., and Slattery, M. K., Ibid., 12, 449-66 (1926). (10) Papish, J., and Hoag, L. E., Proc. Natl. A d . Sci., 13, 726-8 (1927). (11) Slattery, M.K., J . Optical SOC.Am., 19,175-86 (1929). PUBLICATION of this paper delayed at the request of the Office of Censorship.
NOTES ON ANALYTICAL PROCEDURES Device for Automatic Protection of a Diffusion Vacuum Pump THEODORE J. WANG O h i o State University, Columbus, O h i o
lF A
leak occurs in an oil diffusion vacuum system, the hot oil vapor may react with the oxygen of the incoming air to deteriorate the oil and form a sludge which clogs the system. A simple arrangement is herein described which serves to protect the oil in the event of a leak. The scheme consists of utilizing the unbalance voltage developed in a Pirani gage to trigger a thyratron, which in turn opens the diffusion pump heater through a relay. The complete circuit for alternating current operation is shown in Figure 1. The necessary isolation between the bridge supply TO PUMP HEATER
FILAMENT TRANSFORMER
Figure 1, Circuit for Alternating Current Operation
potential and the thyratron operating potentials is secured with minimum expenditure for parts through the use of two 5-volt filament transformers. One transformer supplies the tube heaters, and the other transformer-connected in reverse and fed from the Bvolt output of the first-supplies the rectifier anode. Switch SI has three positions: center, “off”, with the alternate current supply line open; down, “test”, with the Pirani galvanometer connected; and up, “stand-by”, with the thyratron inserted in place of the galvanometer. The value of the gas pressure a t which the pump heater cuts out may be preset by adjustment of the variable bridge arm and the cathode potentiometer. I n the particular constructed setup to which the given values of the components in Figure 1 correspond, the indicating meter used in the test circuit was a Triplet 0-100 direct current microammeter, and the relay employed happens to have been a discarded one of unidentified manufacture. The values of the current limiting resistors rtssociated with both the meter and the relay would, of course, probably have to be changed to accommodate different typesof equip TER ment in these places. It is essential that the grid and anode potentials on the thyratron be in phase, or the tube will not fire. To ensure the proper phase relation it may be necessary to reverse the connections to one (any one) of the four transformer windings. A relay of the lock-in type might be desirable for security. However, in the event of a temporary power interruption a nonlocking relay would serve to restore the pump heat a t the a p propriate time following the interruption when the pressure is again sufIiciently low.
