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ANALYTICAL CHEMISTRY
Quantitative Analysis of Soil Clays with the North American A N D J. L. Phillips ,X-Ray Spectrometer. G. TALVENHEIMO WHITE,Agricultural Experiment Station, Purdue University, Lafayette, Ind.
than that of sodium chloride are required. The use of vacuum makes it ossible to extend the range of analysis from calcium down to tEe next row of lighter elements.
A systematic study was made of factors affecting the qualitative and quantitative estimation of clay minerals present in soil clays. The preferred orientation technique was emploved exclusively. Wyoming bentonite, illite, kaolinite, vermiculite, prochlorite, and glauconite served as "standards" to represent the main clay mineral groups. Some of the factors studied were dialysis, cation saturation, concentration of clay, solvation with various polyhydroxy organic compounds, and relative humidity. Calcium saturation, gl cero1 solvation, and drying at 8% relative humidity produced tge optimum conditions for quantitative analysis. The clay mineral content of soil clays was interpreted in the light of working curves prepared from polycomponent mixtures of bentonite, illite, kaolinite, and quartz. The illite (Pennsylvania underclay) used in these studies possessed an expandable crystal lattice. Existing standard clay minerals appear to be inadequate for the quantitative determination of clay minerals in soil clays, owing t o the preqence of illitemontmorillonite intermediates.
Lattice Constants, Expansion Coefficients, and Atomic Weights of Diamond, Silicon, and Germanium. M. E. STRAUMANIS . ~ N DE. Z. AKA,School of Y h e s and hletallurgy, University of Missouri, Rolla, No.
Application of a Geiger Counter to Weissenberg Single Crystal Intensity Measurements. HOWARD T. Evavs, JR., Philips Laboratories, Inc., Irvington-on-Hudson, N. T. In order to improve the accuracy of intensity measurements made with the Weissenberg camera, the film has been replaced with a Geiger counter. The angular position of the counter arm is measured on a graduated circular plate normal to the spindle rotation axis. The whole instrument is readily interchangeable with the film holder. Provision is made for oscillating the crystal through an angle continuously variable from 0' to 3". Intensity of a reflection is measured by using a wide slit with the Geiger counter fixed, and totalizing the number of counts received while oscillating the crystal through the reflecting angle. The angular settings are either measured directly from the film, or by means of a simple graphical device. Upper level reflections can be brought into the measuring circle by means of the inclination setting. This technique has the same range and the same Lorentz and polarization functions as the normal beam method, In routine operation, each reflection requires about 3 minutes for measurement, and is reproducible t o 1%. The need for accurate x-ray stabilization and proper alignment n-as emphasized. Application of the method to a ipecific case was described. Proportional Counter Design for X-Ray Diffraction Measurements. R. PEPINSKY, Pennsylvania State College, State College, Pa. In order to obtain very high efficiencies and essentially zero dead time for x-ray diffraction intensity measurements, new proportional counters have been designed. These are essentially cylindrical tubes with side-window apertures, and with rare gasmethane fillings. Operation in the proportional voltage range assures rapid counter recovery, and the side-window construction results in elimination of dead space due to electrical end effects of the sort encountered in end-window tubes. Consequently high filling pressures can be used, and high efficiency therewith achieved. The cylindrical counter body is of copper, to which brass end flanges are soldered. The circular end pieces are of Teflon, and these serve both as vacuum gaskets and central-wire insulators. The central wire is spot welded to heavier nickel wire, and the latter is soldered into axially drilled machine screws which are threaded through the Teflon insulators and made vacuum tight by washers and nuts. Before assembly the copper body is cleaned in a brightrdip and washed. Evacuation and filling are through a '/a inch inside diametpr copper tube, which is crimped closed subsequentlp. Windows are either 0.25-inch circular apertures, or long slots parallel to the cylinder axis, nickel or other foil being used for window material. The slot windows facilitate the use of the counter for higher layer line recording in a single-crystal goniometer. Designs are presented of multiwire counters for use with small diameter probe-type fine-focus x-ray tubes. Vacuum X-Ray Fluorescence Analysis Apparatus. L. S. BIRKS, U. S. Naval Research Laboratory, Washington, D. C.
A vmuum Geiger counter spectrometer, designed for fluorescence analysis, was described. Several modifications in the Geiger counter are necessary, and crystals with spacing larger
A picture of the complete setup for most precise lattice constant determinations between 0" and 60" C. was shown. For these determinations no standard substances were necessary, nor any mathematical corrections except that of refraction of x-rays. Expansion coefficientsand atomic weights, if the density is known, can also be calculated ( 2 ) from these data. The lattice constants and coefficients of expansion of diamond, silicon, and germanium are as follows: Diamond. Two varieties of industrial bort and two pure diamond stones of gem quality (courtesy Diamond Research Laboratory, Johannesburg, South Africa) were used for the investigation. Cobalt radiation and a single /3 line (331) in the backreflection region (+ 7.98') were used for the calculation of the constants. Mean lattice constant of diamond a t 20' C. (corrected for refraction): 3.55963 * 0.00002 kx. Coefficient of expansion of diamond calculated from present data taken between 10' and 50" C.: 1.18 X loF6. Coefficient of expansion of diamond determined by Fizeau: 1.18 x 10-6. Atomic veight of C in diamond (calculated): 12.0099 (chemical weight 12.010), using 3.5148 at 18' as the mean value of density determinations of Bearden ( 1 ) and Tu ( 3 ) . The deviation of the present value of the lattice constant from those obtained hv other investigators was discussed. Silicon. The hyperpure silicon sample (99.9i0', Si) was obtained from the Du Pont Co. The lattice constant was determined using Cu radiation and a single a1 line (444) with + 10.70". The a2 line (444) is superposed by the P line (731) and hence too broad for measurements. Mean lattice constant of silicon at 20" C.:5.41987 * 0.00004
=
=
kX.
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Germanium. Metallic germanium of better than 4 9's purity wa5 obtained from the Eagle-Picher Co. Cr radiation and a,and a2 lines (422) with + E 7.15' were used for the calculation of the constant, which at room temperature was found to be 5.64602 kx. The coefficients of expansion, atomic weights, and densities of silicon and germanium were discussed. ( 1 ) Bearden, J .4.,Phys. Rea., 54, 654 (1938). (2) Straumanis, M. E., J . Applied Phys., 20, 726 (1949). (3) Tu, Y . , P h y s . Ret., 40, 662 (1932).
Society for Applied Spectroscopy The Society for Applied Spectroscopy will meet at 6 p.>f. January 9 for informal dinner at Tosca's, 118 Fulton St., Xew York, and for its regular meeting at 8 P.M. at the Socony-Vacuum Training Center, 63 Park Row, Harold K. Hughes of the Socony-Vacuum Laboratories will speak on "Quantitative Chemical Analysis by X-Ray Absorption Spectroscopy." Fourth Symposium on Analytical Chemistry. Louisiana State Univeraity, Baton Rouge, La., January 29 t o February 1, 1951 Chemical Institute of Canada, Division of dnalytical Chemist r y . Mount Royal Hotel, Montreal, Canada, February 15 and 16, 1951. Third annual regional conference Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy. William Penn Hotel, Pittsburgh, Pa., March 5 to 7, 1961 Fourth Annual Summer Symposium. U'abhington, D. C., June 14 to 16, 1951
