INDUSTRIAL AND ENGINEERING CHEMISTRY
40
distinctly separated from lines produced by other minerals present in the sample to be analyzed, and it should be as near as possible to the line of the substance sought, SO that the two will undergo the same absorption effects and will have nearly the same general background fogging. Using the technic described here, a separation of 0.3 mm. is satisfactory for good resolution. Since each crystalline substance present in the sample gives several diffraction lines, a suitable line may be found in almost every case for the satisfactory application of the method. TABLE111. RESULTS OF ANALYSES Sample
Material
~ Q u a r t a X-ray Microaco ic method metho]
% K K K K K K
K
K K K
1 2 7a 8a go 21 22 23 24 25
Mine dust Mine ore Feldspar Corundum Abrasive wheels Mine dust Mine dust Mine dust Mine dust Mine dust
24.5 31.5 26.0 Less than 1 Less than 1 3.5 13.2 54.6 16.7 13.4
%
..
33:8 0.8
8.3
.* .. .. ..
..
These samples were obtained from the Research Laboratories of the Aetna Life Insurance Company, Hartford, Conn., and were examined there for quartz by the petrographic immersion method. 5
TABLEIV. TEST OF X-RAYMETHOD(8) Sample No. 2 with added quartz No, 22 with added quartz
Quartz Found 37.0 54.6
Quartz Calculated 35.5 66.6
The apparatus used is necessarily expensive, but no more so than that required for dependable analysis with the quartz spectrograph. Aside from the time required for the long grinding operation, an analysis may be completed in about 4 hours. The method should find ready application to many other industrial problems, such as those encountered in the manufacture of cement, plaster, and allied products, in identification and quantitative estimation of intermediate and final products in industrial processes, and in any case in which an
A Sensitive Check Valve E. L. GREEN
U. S. Department o f Agriculture, Bureau o f Plant Tndustry, Washington, D. C.
I
N precipitating copper by hydrogen sulfide, a number of determinations were lost because of accidental interruption of the gas stream before all the solutions in the train had been saturated. Partial vacua developed where these unsaturated solutions took up the gas in the connections, and finally the solutions in the flasks backed up into the scrubbing devices. To prevent any such movement, an unusually sensitive check valve was required for the gas delivery tubes. The device illustrated has served this purpose. The outer shell, A , is an ordinary 25-mm. (I-inch) test tube cut to a suitable length. B is made by sealing a piece of 4-mm. tubing to a piece of 15- t o 18-mm. test tube of the indicated length. A t point C the neck of part D is ground into B t o an airtight seat. To avoid sticking, this joint should have a blunt rather than a
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exact quantitative knowledge of the chemical or mineralogical composition of a mixture is necessary or desirable. The authors are a t present using the method to study the kinetics of the change of some oxides from one allotropic form to another in the dry state, and it has been applied with success to the compounds of lead in storage battery research.
Summary An empirical method for the quantitative analysis of mine dusts in terms of their mineralogical content using x-ray diffraction is described. A crystalline compound which is not present in the dust sample is added to it in a definite ratio. The densities of a diffraction line of the constituent sought and of a line of the added substance are compared photometrically. From the ratio the amount of the substance sought may be determined by reference to a curve in which similar ratios are plotted against per cent substance sought, the curve being prepared using synthetic standard samples of known composition. Duplicability of results is within 5 per cent of the amount of the substance sought in the case of quartz. The method has been applied only to quartz-silicate ore mixtures, ranging between 0 and 100 per cent, but should prove applicable to many other minerals.
Literature Cited (1) Clark, G. L., “Applied X-Rays,” 2nd ed., New York, 1932, McGraw-Hill (complete discussion of x-ray diffraction by crystalline powders). (2) Clark and Reynolds, Univ. Toronto Studies, GeoZ. Ser., No.38,13 (1935). (3) Hull, A. W., J . Am. Chem. Soc., 41,1168 (1919). (4) Knopf, U.S. Pub. HeaZthRepts., 48,183 (1933). (5) Ross and Sehl, IND. ENQ.CHEM.,Anal. Ed., 7,30 (1935). (6) Scheibe, “Chemische Spektralanalyse, physikalische Methoden der analytischen Chemie,” Vol. I, p. 108, Leipzig, Akademische Verlagsgesellschaft, 1933. (7) Ibia., pp. 125-30. (8) Walker, Univ. Toronto Studies, Geol. Ser., No. 38,5 (1935). RECBIVBD September 26, 1935. Presented before the Division of Physical and Inorganio Chemistry at the 90th Meeting of the American Chemical Society, San Francisco, Calif., August 19 to 23, 1935.
long taper. Part D is made from a 10-mm. test tube. A tail is drawn on the upper end to guide it into its seat. A tail on the lower end serves as a handle during the grindihg ’and is then sealed off. When D is finished it must float less than half submerged in water. With D in place, the lower end of B is softened and threeindentations are pressed into it t o retain D. I n use, as small a quantity of water as will serve is placed in A . A current of gas entering through B displaces the water from it into A and D falls away from its seat. As soon as the current of gas tends to reverse, the water rises inside B and floats D into its seat. Areverse pressure too slight to close one of these valves but still capable of backing gas through it is impossible. R B C E I ~ ENovember D 9. 1935.
