423
V O L U M E 28, NO. 3, M A R C H 1 9 5 6
110. Tripotassium Silver Tetracyanide, K,Ag(CN),
C 0 R R E S P 0 N DEN C E
Analysis of Micron-Sized Particles
E U G E N E STARITZKY and F I N L E Y H.ELLINGER, The University of California, Lor Alamor Scientific Laboratory, Lor Alamor, N. M.
silver tetracyanide is prepared by evaporating Ta t room temperature an aqueous solution containing potasStabilRIPOTASSIUM
sium clanide and silver cyanide in the molar ratio 3 to 1. ity relations of this compound in the system KC?;-AgCr\;-H20, at 25' C. have been studied by Bassett and Corbet ( I ) , who, however, erroneously assigned to it the formula K3Ag(Ci\;)4.H20. The silver salt is isomorphous with KsCu(CP& the composition of which is well established.
Partial Pow-der X-Ray Diffraction Pattern of KZAg(CN)h hkl
119 101 211 209 201 2ii 22? 21 1
310 321 201 329 211 301 332 32i
411, 330 400 420 312
d , A., Calod. 6.139 4.940 3.918 3.849
3.181
3.036 2.938 2.852 2,607 2.525 2.470 2.383 2.352 2.292 2.134 2.090 2.047 1.925 1.891 1.867
d , A.h Obsd. 6.14 4.94 3.92 3.84 3.18 3.04 2.947 2.853 2.598 2.529 2.468 2.381 2.350 2.295 2.140 2.088 2.048 1.920 1.893 1.863
I/Ilh 95
30 60 70 35 55
20 100 15 65
10 15
.
10 10 10 20 15 25 15 15
Pliilips 114.6-mm.-diameter powder camera, Straumanis mounting; = 1.5418 4. Relative peak intensities above background from densitometer nieasurernents. a
Determination of Particle Size SIR: It has been suggested (2) that, in Lodge's Millipore technique for fine particle analysis, it should be possible to derive a relation between the size of the reaction spot, or halo, and the original particle size, as Seely ('7) and Pidgeon (6) had done for the gelatin test for halides. Tufts and Lodge (8) have discussed some of the errors inherent in such a relationship. They point out that, if such a calibration is made-for example, for the halide test, using sodium chloride, the error caused by assuming this calibration to hold for all halides of natural atmospheric origin will be less than the other errors of the method. An investigation was made to determine these relationships for several reactions on Millipore. GENERAL METHOD
The technique used was fundamentally similar to Seely's ( 7 ) . Particles of a known species were collected. The Millipore filter was cut in two; one half was examined directly, and the other half was treated chemically to develop the characteristic reaction spots for the ion under study. Both particles and halos were counted by size classes in identical-sized areas; if the total numbers of halos and particles differed greatly, the sample was rejected, and the experiment was repeated. If this was unsuccessful, study usually revealed that the smallest particles gave no visible reaction spots, and thus the lom-er limit of identification was established. The particle and halo counts by size class were then compared. It was assumed that the largest halos were derived from the largest particles, the next largest halos from the next largest particles, etc. Thus, if the tenth largest halo was 50 microns in diameter, the diameter of the tenth largest particle was determined (customarily from smoothed distribution curves).
X(CuKo) 6
CRYSTAL MORPHOLOGY System and Class. Trigonal, trigonal-trapezohedral. Axial Element. CY = 74" 7'. Habit. Rhombohedrons ( 110), occasionally with the base (111/ . Polar Angle. (110) A-(O11) =-76' 55'. Interzonal Angle. [ l l l ]A [ l l l ] = 79" 22'. X-RAYDIFFRACTION DATA Space Group. R32 (Di).-4strong effect M as ob- piezoelectric _ served. Cell Dimensions. ao = 8.19 A.; CY = 74.2'; cell volume 497 A. 3 Formula Weights per Cell. 2. Formula Weight. 329.24. Density. 2.20 grams per cc. (x-ray); 2.18 (flotation).
RELATIONSHIP B E T W E E N PARTICLE A N D HALO DIAMETER C A L C I U M TEST 0 MAGNESIUM TEST X - - - H A L I D E TEST N I T R A T E TEST +
-
* 0
48
-----
/7
1
OPTICALPROPERTIES Uniaxial negative, Refractive Indices (5893 A.). no = 1.521; n E = 1.516: geometric mean 1.5193. Molecular refraction 45.5 cc. (based on xray density). Colorless. LITERATURE CITED
y/
(1) Bassett, If., Corbet, A. S.,J. Chem. Soc. 125, 1660-75 (1924). CONTRIBUTIONS of crystallographic data for this section should be sent to Walter C. MoCrone. 3140 South Michigan Ave., Chicago 16, Ill. W o r k done under the auspices of the Atomic Energy Commission.
Figure 1.
I
I
2
4
I
I
6 8 P A R T I C L E D I A M E T E R , ,u
I 13
I2
Approximate calibration curves for five reactions on Millipore
Aaauming that test substances are representative of their dao-
,424
ANALYTICAL CHEMISTRY
These were said to correspond, and a graph lvas made of halo 2’s. particle size. If possible, an analytical expression was derived for the relationship. Where this was a straight line through the origin, the slope-Le., the ratio of halo to particle size-was determined, and was termed the “growth factor.” These are shorn-n in Figure 1 : det’ails of the determinations are given below. SPECIFIC TESTS
Halides Other Than Fluoride. The refractive index of sodium chloride, the test material, was found to be so close to that of the filter material that it was difficult to measure the particles accurately. .\ccordingly, the following method was used, which appears to have generai utility in such cases.
A large drop of dry redistilled acetone was placed on a microscope slide, and the half filter bearing the unreacted part.icles was rapidly placed upon it. \Then the acetone had evaporated, a clear, cellophanelike membrane remained, with the salt particles embedded in it. This was immersed in dist.illed water for 0.5 hour, then dried. Thus, air-filled replicas of t,he particles were obtained which Tvere clearly visible under the microscope. The mathematical treatment described above yielded the results shown in the figure. The physical evidence indicated that a line through the origin should be expected. This line is shown, and yields a growth factor of 4 i 3 . This value has already been used in several published studies (3-5). Sulfate Ion. Sodium sulfate was used as the test material. Sodium sulfate is weakly anisotropic, and hence the crystals may be distinguiqhed by the use of crossed polaroids. Thus the replira method was not necessary. The best line through the origin yields a growth factor of 1.68. Nitrate Ion. This was treated in the same manner as the sulfate. Because the reaction spots were radiating clusters of fine needles, frequently unsymmetrical in appearance, the halo diameter used was that of a circle of equal projected area. This is obviously subjective, but after some practice gave reproducible results. S o halos were found corresponding to particles smaller than 2.0 microns. This presumably represents the lower limit of identification for this method. The best straight line obviously does not pass through the origin. It has the equation d h = 3.73 d, 6.29, where d h is halo and d, is particle diameter. Magnesium Ion. I t was necessary to u8e dry, powdered magnesium sulfate in order to obtain dry crystals for examination. Fading of the halos was retarded by not u-ashing the filter after chemical treatment. The gram-th factor was found to be 1.88. Calcium Ion. Here again it was necessary to use a dry powder spray. The test substance was calcium acetate. The halopart,icle relationship does not appear to be a simple one.
+
CONCLUSION s It is possible to determine particle size spect,ra for a number of chemical species. It seems possible that’ this technique could be
extended furt,her to other ions. Field tests have shown that the halide technique yields highly satisfactory results, giving the expected logarithmico-normal distribution, u-hich also obeys Junge’s ( 1 ) “r-cube” law. ACKNOWLEDGMENT
The authors wish to t,hank Horace R . Byers and Roscoe R. Braham, Jr., of this laboratory for many helpful discussions. The research reported in this paper has been sponsored by the Geophysics Research Directorate of the Air Force Cambridge Research Center, Air Research and Development Command, under Contract AF19(604)-618. LITERATURE CITED
(1) (2) (3) (4) (5) (6)
Junge, C., Tellus 5, 1 (1953). Lodge, J. P., ANAL.CHEY.26, 1529 (1954). Lodge, J. P., J. Meteorol. 12, 493 (1955). Lodge, J. P., Baer, F., Ibid., 11, 420 (1954). Lodge, J. P., McDonald, J. E., Baer, F., Ibid., 11, 315 (1954). Pidgeon, F. D., ANAL.CHEY.26, 1832 (1954).
(7) Seely, B. K., Ibid., 24, 576 (1952). (5) Tufts, B. J., Lodge, J. P., Ibid., in press. Cloud Physics Project Department of Meteorology University of Chicago Chicago 3 i , Ill.
JAYES P. LODGE,J R . * H24XX1*F. R O S S ~ WILLIAMK. S U M I D A S BARBAR.4 3. T U F T S
1 Present address, Robert A . Taft Sanitary Engineering Center, 4676 Columbia Parkway, Cincinnati 26, Ohio. 2 Present address, 7304 Forest Road, Hyattsville. RId. * Present address, Ceramics and Minerals Department, Armour Research Foundation, 3427 South Federal St., Chicago, Ill.
MEETING R E P O R T
Society for Analytical Chemistry of the Microchemistry Group of the society A w.t h meeting the Mid-Southern Counties Section of the Royal JOIST
Institut,e of Chemistry was held in Southampton Oct. i, at, which the folloning papers were presented and discussed. Trace Elements in Archeology. C. F. M. FRYD,D e p a r t m e n t of Government Chemist, Government Laboratory, Clements I n n Passage, Strand, London, W. C. 2. Recent extensions of public interest in archeology h a r e been accompanied by a widening of t h e scope of t h e analyst in t h e examinat,ion of archeological specimens. T h e archeologist today relies on the chemist not only to help him in the exposure of occasional fraud, b u t much more frequently to assist in t h e dating of a specimen, either directly when a time scale can be established for the accretion or removal of an element, or comparatively when one specimen can be presumed by reason of intermediate chemical characteristics t o fall chronologically between two known specimens. T h e trace elements are important in this respect and their examination is not without interest.
.
Methods for Determining the Trace-Element Status of Plants.
E. J. HEWITT, University of Bristol, Agricultural and Horticultural Research Station, Long h s h t o n , Xr. Bristol. I t is possible t o recognize changes from the optimum states of trace-element availability for plants in three ways-by soil analysis, by plant analysis, and by physiological studies. T h e first was not considered further. Physiological studies may be partly visual, but they require detailed knowledge of plants; t h e symptoms of deficiency may be confused by other disorders and be already serious by the time they could be seen. Alternatives were fertilizer trials, pot cultures, or spraying or injecting trace elements. Plant analysis is usually made on physiologically active regions of the specimen. If stringent precautions are taken to avoid contamination, especially from soil, reasonably consistent results are obtained by different analysts, except for boron and iron. One difficulty is t h a t the metal content may v a r y considerably with t h e portion of t h e plant taken; another is t h a t plants could show deficiency symptoms for a particular metal b u t might contain not very much less t h a n a healthy plant-the diagnostic value of chemical analysis is then not great. Work in his own department had indicated particular difficulties t h a t might arise with iron. Estimation of Trace Elements in Plant Material and Soils by M e a n s of Aspergillus niger. D. J. D . NICHOLAS, University of Bristol, Agricultural and Horticultural Research Station, Long Ashton, Nr. Bristol. T h e mold Aspergillus niger has been used as a test organiam t o determine copper, zinc, manganese, and molybdenum in soils, plant and animal tissues, and in enzymes. Experimental methods have been developed for t h e preparation of standard growth series for iron, zinc, copper, manganese, and molybdenum. T h e pure culture methods include purification of culture solutions by chemical or ion exchange procedures and t h e preparation of glassware and inocula free from trace metals. T h e bioassay method is preferred to chemical procedures because of its higher accuracy and specificity a t low concentrations of t h e metal.
At a meeting of the Physical Methods Group on Kov. 30 the following officers were elected: chairman, J. E. Page; vice chairman, R. A. C. Isbell; honorary secretary and treasurer, L. Brealey, 417 High Road, Chilwell, Kotts.
