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pentoxide 38.0, for acetone 41.4, and for diethyl ether 32.9, all being of approximately the same order. From a composite curve of the present authors’ data on n-amyl mercaptan, taking values for K of from 30-150 seconds, a coefficient of 5.08 is obtained for the range 425-475” C., which gives 1.384 for 10” C. intervals, a heat of activation of 33,800 calories, and E/RT at 24.6. Should it be necessary to invoke chain reactions to explain the speed of such unimolecular reactions, the thermal decomposition of mercaptans may be formulated as follows: CnHZn+ISH +(aHzn+l SH (1) CnHzn+lSH SH +HzS CnHznSH (2) CnHznSH +CnHZn SH (3) The assumption is made of scission into free radicals. The recombination of these free radicals then becomes statistically very improbable. Equation ll however, is only a trigger reaction, and Equations 2 and 3 constitute a plausible chain thereafter. The following may also be written:
+
+
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Equation 4 is a companion reaction to Equation 1 and would be evinced by a small yield of saturated hydrocarbon. Otherwise the chain goes on as before, Acknowledgment The authors wish to acknowledge the cooperation of C. E. Anding, Jr., in the development of the refinements of the analytical determinations of mercaptans and the helpful criticism of J. B. Hill and L. M. Henderson.
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Literature Cited (1) Borgstrom and Reid, IND. ENO. CHEM.,Anal. Ed., 1, 186 (1929). (2) Elgin, IND. ENG. CHEM.,II,1290 (1930). (3) Faragher, Morrell, and Comay, Ibid., I D , 527 (1928). (4) Hurd and Meinert. J. A m . Chem. Soc., 62, 4978 (1930). (5) Kahn, Bull. SOC. chim. Roumania, 6, 70 (1923); C. A . , 18, 1467 (1924). (6) Lachman. J . A m . Chem. Soc., 46, 2358 (1923). (7) Liebermann and Seyewitz, Ber., 24, 788 (1891). (8) Reed and Theriault, J. Phys. Chem., S6, 673 (1931). (9) Sabatier and Mailhe, Comfit. rend., 160, 1569 (1910). (10) Taylor, J . Phys. Chem., 54, 2761 (1930).
Composition of Mechanical Separates from Ground Phosphate Rock’ W. L. Hill, H. L. Marshall, and K. D. Jacob FBRT~LIZER AND FIXED NITROGEN INVESTIGATIONS, BUREAUOF CHEXISTRYAND SOILS,DEPARTMENT OF AGRICULTURE, WASHINGTON. D. c .
When samples of the various commercial types of domestic hard phosphate rock are ground by a uniform procedure to pass a 100-mesh sieve, there is considerable variation in the distribution of particle size with the different samples, particularly in the %and” and 66clay” fractions. This is due not only to variations in the physical character of the phosphates themselves but also to the presence of variable quantities of impurities, such as quartz and silicates. In general, the high-grade phosphates contain the lowest percentages of “sand” and the highest percentages of “clay” particles. In the case of the Florida phosphates, the silica concentrates to a marked extent in the “sand” fractions, while in the case of Tennessee brown-rock phosphate it tends t o concentrate to R slight extent in the ‘Isand” and “clay” fractions. Silica concentrates to a marked extent in the %ilt” and 66clay’’fractions of Idaho and Wyoming phosphates.
In general, there is considerable concentration of the iron and aluminum in the Way’’ fractions of the ground phosphates. In general, calcium and phosphorus follow the same trends in the different fractions. They tend to concentrate slightly in the “silt” and “clay” fractions of the Florida phosphates, and in the L6silt”fractions of Tennessee brown-rock phosphate, while they concentrate to a considerable extent in the “sand” fractions of Idaho and Wyoming phosphates. An approximate estimation of the distribution of phosphorus pentoxide in the mechanical separates from ground samples of commercial phosphate rock may be made directly from the results of the mechanical analysis. There is a small but progressive increase in both the ammonium citrate and the citric acid solubility of the phosphorus pentoxide of phosphate rock as the particle size decreases.
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I
T HAS been shown ( 3 , 4 ) that, in general, there is consider-
able variation in the chemical composition of the different sizes of particles separated mechanically from natural finely divided phosphates, such as the waste-pond and soft phosphates of Florida. Inasmuch as similar data were not available for the domestic types of hard phosphate rock that had been concentrated for commercial use by the customary methods, a study was made of the chemical composition of the various ranges of particle sizes separated mechanically from several ground samples of these materials. The results of this invest.igation are given in the present paper. Materials Used
FLORIDA LAND-PEBBLEPHOSPHATESampleS 910 and 912 were low-grade and high-grade materials, respectively, I R e c d v e d M a y 23, 1931.
from deposits near Mulberry, Polk County. Sample 947 was a low-grade material from a deposit near Brewster, Polk County. FLORIDA HARD-ROCK PHOSPHATE-Sampk 932 was a highgrade material from a deposit near Dunnellon, Marion County. TENNESSEE BROWN-ROCK PHOSPHATE-sampleS 906 and 908 were high-grade materials from deposits near Wales, Giles County, and Mountpleasant, Maury County, respectively. WYOMING PHosPHAm-Sample 948 was a low-grade material from a deposit near Cokeville, Lincoln County. IDAHO PHosPHAm-Sample 973 was a medium-grade material from a deposit near Conda, Caribou County. The Florida and Tennessee phosphates were concentrated for commercial use by washing, screening, and drying; the
October, 1931
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Table I--Physical Composition of Phosphates
SAMPLE
TYPEOF PHOSPHATE
“SAND”147-50p Large scale Pipet separation method
%
%”
“SILT”50-5p Large scale Pipet separation method
%
“CLAY”
