Crop and Soil Reactions to Applications of Hydrofluoric Acid W. H. MACINTIRE, S. H. WINTERBERG, L. B. CLEMENTS, L. J. HARDIN, AXD L. S. JOXES The University of Tennessee Agricultural Experiment Station, Knoxville 16, Tenn. T h e experimental objective was to determine effects that hydrofluoric acid, as increments derived directly from the atmosphere, induces upon soil reaction and fertility, upon seedings, upon subsequent plant growth, and upon the uptake of fluorine. Yields, fluorine uptake, and soil acidity were not affected significantly by applications of hydrofluoric acid that were in simulation to increments that would be expected to reach the soil through rain and dew in contrast to the effects induced by parallels of hydrochloric acid. In a humid region, soils of the type used would not be rendered less fertile through increments of effluent hydrofluoric acid in quantities that would be expected to come directly from the atmosphere at points not immediate to emissions. Under such conditions, and with adequacy of calcium in the soil, possible enhancements in the fluorine content of forage vegetation would be chargeable to its pollution directly from the atmosphere rather than to uptake from the soil.
streamp, and ponds in the localities affected, and the effects that such occurrences exert upon plant and animal life in those localities. The chemical aspect of the field work is being supplemented arid amplified through laboratory, pot culture, and lysimeter studies of the passage of the fluorine ion from incorporations of various fluorides and rock phosphate into forage crops and into the rain water leachings from lysimeters. OBJECTIVES
A particular phase of the project relates to the immediate and subsequent effects that air-derived increments of hydrofluoric acid exert upon soil systems and upon the fluorine content of subsequent vegetation. This paper deals with the early effectn that applications of hydrofluocic acid exerted upon two distinctive soils, unlimed and limestoned, upon the occurrence of Huorine in red clover grown thereon without the contamination that can occur in the field, and also the comparative effects of the ions of fluorine and chlorine from equivalent applications of hydrofluoric acid and potassium fluoride, and hydrochloric acid mid potassium chloride. Rerause fluorine does not aiid cannot occur in its elemental state in the atmosphere (S), the use of the word fluorine in the present text connotes the presence of the element a3 a component,.
L
IVESTOCK production, floriculture, and horticulture are purported to be affected adversely in certain localities where the atmosphere has been contaminated through fluoric emission6 from manufacturing operations. I n 1943, 29 industrial pi ocessei were listed ( l a ) as causing such emissions from components iiative to the materials processed or from additive reactants, such as fluorspar, 406,000 tons of which were used in 1949 ( 2 ) . Fluoric compounds are dispelled from five distinct operatiom in the processings of rock phosphate and of slag in Maury County of middle Tennessee, but in Blount County of east Tennehsre the emissions are from a major operation in which molten cryolite is used as the solvent for alumina in the manufacture of aluminum. In both counties, however, the emissions are chiefly hydrofluoric acid, the dispersion of which may occur as a gaseom phase, as mists, as fogs, and as droplets, according to discharge volume, distance, topography, prevailing winds, and other meteorological conditions and to concomitant ocrurrence of particulates and aerosols. Many farmers in the two Tennessee counties now contend that the fluoric emissions contaminate their forage crops and that the ingestion of the contaminated vegetation is causing their liveetock to suffer the tooth, bone, and degenerative effects that spell fluorosis (1). Because of such contentions, and because the Middle Tennessee Experiment Station is located near the sevei a1 011erations that process rock phosphate and slag in Maury County, and because the university owns an experimental farm near the aluminum operations in Blount County, the Agricultural Experiment Station inaugurated an over-all chemistry-animal husbandry study of the effects of atmospheric effluents upon plant and animal life in the two designated locales. The urgency of the situation was recognized by several organizations among those that operate in the two counties and they are cooperating and collaborating in the furtherance of the current investigation. The jointly-conducted study developed quickly into the Agricultural Experiment Station’s current survey to determine fluorine occurrences in vegetation, soils, air, and in waters from rain,
EXPERIMENTAL
SOILSAXY PRELIMIKARY TREATMEKTS. The charactci,i$tics of the Hartsells h e sandy loam and t’heClarksville silt loam used in the 2-gallon pot cultures of Tables I and I1 are indicated by the analytical values given in Table I of the preceding paper ( 8 ) . These values show fluorine contents of 169 parts per million (p.p.m.) and 160 p.p.m. of fluorine, respectively, and initial p1-l values of 5.2 and 5.9. I n series A, B, and C, the two soils were limestoned at the respective rates of 4 tons and 2 tons of calcium carbonate per acre surface as detailed for these and the supplemental inputs in footnotes to Table I. All pots received per-acre inputs of 160 pounds of phosphorus pentoxide, as monocalcium phosphate, and 185 ounds of potassium sulfate along with a solution that supplief boron, mangancse, copper, and zinc in appropriate quantities. FLUORINE APPLICATIOKS.The fluorine applications were supplied through 200-ml. solutions of hydrofluoric acid that provided fluorine at rates of 100, 400, and 800 pounds per acre surface. Those amounts were equivalent, respectively, to the fluorine in 1.25, 5, and 10 tons of rock phosphate. The hydrofluoric acid applications penetrated to a depth of 0.5 inch. h f k r t,he 6 days allowed for reaction, red clover was seeded to the soils of the four series of Table I. Single applications of hydrofluoric acid effected conditions more intense than those that would ensue from cumulative increments of corresponding quantities of hydrofluoric acid from the atmosphere and from rain waters over an extended period. RESU L l S
Dry weights and determinations of fluorine content of the red clover and the final p H values of the several soil systems are given in Table I and the crops are pictured in Figure 1. HARTSELLS SOIL. On this unlimed soil, the 100-pound application of fluorine induced no observable effect upon the growth of clover and did not enhance its content of fluorine, while causing
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
August 1951
TABLEI. EFFECTS OF APPLICATIONS OF HYDROFLUORIC ACID TO
THE
1801
SURFACEOF T w o SOILS
(As registered b y clover response a n d fluorine content, a n d b y soil pH)
Fluorhe Applications, Lb./AcreQ
Unlimed Series Dry Crop Weight, Fluorine, grams p.p.m.
Soil, pH
Series A D r y Crop Weight, Fluorine, grams p.p.m.
-
Soil, pH
Limestonedb Series B
D r y Crop Weight, Fluorine, grams p.p.m.
Soil, pH
Series C D r y Crop Weight, Fluorine, grams p.p.m.
Soil, pH
On Hartsells Fine Sandy Loam None 100 400 800
Sone 100 400 800
9.6 9.2 1.1 0.2
16.5 14.5 10.3 3.8
16
19 82
14
19
86 150
5.1 5.0 4.6 4.6 5.5 5.4 5.3 5.0
13.2 13.1 12.2 10.9
16.7 16.8 15.9 13.2
2o 18 24 44
6.6 6.6 6.1 5.8
13.2 12.0 11.6
20 21
6.6 6.5
11.3
19
23
6.8
On Clarksville Silt Loam 13 6.9 16.7 15 6.7 17.1 28 6.2 15.7 92 5.8 14.7
13 20 29 44
7.0 6.8 6.6
6.8
6.9
11.4 11.4 10.9
10.7
11 12 23 25
6.7 6.8 7.0 7.1
15.3 16.0 15.5 14.1
15 16 22 43
6.9
7.0 7.0 6.6
The applications of H F were preceded by incorporations of phosphate and potash. The acid, in 200-ml. constant, was sprinkled on the potted soil. After 6 days for reaction, the,upper i / 4 zone was removed, mixed, and replaced. I n every case half of the 44011 a n d 2-ton incorporations of limestone to Hartsells a n d Clarksville, respectively, was incorporated into the lower half of soil. b I n series A, the other half of the limestone was mixed into the upper half of soil before the application of H F . I n series B, the limestone incorporation was as in series A ; but a supplement equivalent t o the H F was mixed into the upper '/a of soil before the application of the acid I n series C a/( of the limestone input was incorporated into the lower 3/4 of soil, b u t the added H F was allowed 6 days for reaction with the acidic soil'before the up'per I/q zone was limestoned a t rate, plus, as in series B. (1
only slight lowering of soil pH. The 400-pound application lesIn the upper 2-inch zone, w-here the two larger applications of sened the crop, enhanced its fluorine content to 82 p.p.m., and hydrofluoric acid had been offset through supplemental inlowered the p H of the soil. The 800-pound application proved corporations of limestone, each final pH value was 6.8. almost lethal to the clover; it imIn series C, the three rates of hyparted a high content of fluorine to drofluoric acid application resulted in the subnormal crop and lowered soil crops that were slightly less than the corresponding crops on series A and pH appreciably. The 100-pound application of fluoinduced final p H values somewhat rine induced little effect upon crop above those induced in series B. The response on the limestoned soil of 400- and 800-pound applications imseries A. The 400-pound application parted fluorine contents that were induced a n increase in occurrence of twice the content resultant from the fluorine in the clover, but the in100-pound applications. I n this series crease in uptake was decidedly less a considerable fraction of the applied than that in the meager crop from hydrofluoric acid must have reacted the 4OO-pound application on the with the bases and alumino compounlimed soi1. The 800-pound applinents of the acidic soil and, therefore, cation repressed the growth of clover a larger fraction of the subsequent considerably and enhanced greatly offsetting supplement of limestone the content of fluorine in the crop. was present to cause elevation of pH. At present, however, the repressive CLARKSVILLE SOIL.On this unlimed effect cannot be attributed unqualisoil of less exchange capacity, the 100fiedly to toxicity of the fluorine ion, pound application caused a slight deper se. crease in growth of clover, that On the limestone soil of series A, showed some increase in its fluorine the 400- and 800-pound applications content and induced slight lowering of' fluorine induced respective final of soil pH. The 400-pound applicapH values of 6.1 and 5.8 in the upper tion caused significant decrease in the 2-inch zone, against a pH value of growth of clover on the unlimed soil, 6.6 for both the 100-pound applicainduced an increase to 86 p.p.m. of tion and the limestoned soil to which fluorine in the smaller crop, and lowhydrofluoric acid had not been apered the soil pH value to 5.3. The plied. Apparently, the two heavier 800-pound application proved almost applications of hydrofluoric acid lethal to the clover, the meager crop of t effected respective decompositions of which showed the maximum of 150 1502 pounds and 3104 pounds of calp.p.m. of fluorine, and lowered soil cium carbonate against the onepH values to 5.0. fourth portion, or 2000 pounds, of the The 100-pound application regisFigure 1. Effects of Applications of Hyover-all incorporation that had been tered no definite effect upon either drofluoric Acid upon Response by Red proportioned to the limestoned upper crop or soil on the limestoned series A. Clover on Unlimed and Limestoned 2-inch zone. The 400-pound application registered Hartsells Soil In series B, the red clover responded its effect upon the clover more through Left to r i g h t . Fluorine applications: None, 100, 400, and 800 lb. as in footnote to Table I alike to three rates of fluorine applicaan increase in the fluorine present A . Unlimed B . Limestoned, as in series A tions and the parts per million of in the crop than through decrease in C. Limestoned, as in aeries B fluorine in the crops were similar. plant growth, and through a further D . Limestoned, as in series C
INDUSTRIAL AND ENGINEERING CHEMISTRY
1802
Vol. 43, No. 8
aiid resultant calciun~chloi+de, whereas the 400- and 800-pound both fluorine a i d chlorine were lethal to the millet. Again, the hydrofluoric acid exerted little effect upon final p H values, whereas each hydrochloric acid application effected a decided lowering of pH. In the parallels for potassium fluoride arid potassium chloride applications, which were equivalent to the corresponding applicatiom of hydrofluoric and hydrochloric acids, t8he200-pound a p plication of fluorine, and of chlorine, did not repress plant growth on Hartsells or on Cla,rksvillc soil. The 400-pound application of each halogen was somewhat repressive upon the millet on both soils, whereas the 800-pound application of fluorine as potassium fluoride u-as let'hal to it on both soils. rllthough the three applicat,ioiis of the chlorine ion as potassium chloride repressed plant growth on the highly acidic Hartsells soil, they induced crop increases on the less acidic Clarksville silt loam. The npplications of potassium fluoride caused significant elevations in pH on both soils, with progression in relation to the quantities applied, \Thereas the corresponding applications of potassium chloride induced little change in the f i i d pH values on either soil. The determinations of fluorine content of the crops that responded to the 200 pounds of fluorine show the usual relationship in increase in the occurrence of fluorine in subnormal crops on acidic soils. Because of the several earlier arid present findings:
T A B L E 11. COMPARATIVE EFFECTS O F EQUIVALENT APPLICAapplications of TIOXS O F SOLUTIONS O F HYDROFLUORIC ACID, HYDROCHLORIC
ACID, POTASSIUM FLUORIDE, AND POTASSIUM CHLORIDE TO Two SOILS (-4s registered by millet respoIise,!and fluorine oontent, and by soil pH) On Hartsells Fine Sandy On Clarksville Silt Loam, Applioat,ions Loam, Ciiilimed Unlimed as E uivalencos Dry Fluorine Dry Fluorine of %luorine, *-eight, cont.ent, Final weight, content, Final Lh./Screa gram p.p.m. pH grams p.p.m. pH Noneb 12.8 7 4.4 15.2 9 5.0 FT F --. 200 400
800 H C1
200 400 800 UF __.
9.2
Sone None 3.2
Sone ?;one
200
13.7
800 ---. KGi
None
400
200 400 800
11.2 9.2
5.8 3.1
18
.. ..
I1 , ,
..
4.5 4.4 4.6 4.1 3.9 3.5
8.2
None None 13.0
None None
8 13
!.8
.
0.0 5.8
None
15.6 10.0
!I 5 11
4.5 4.4 4.3
18.4 17.3 17.9
2%
. .. ,
7
..
.. s
20
..
4..9
4.8 4.9 4.4 3.8 3.4 5.4 6 1 6.7
4.8 4.9 4.6
e 1 1 1 agplications were made to aoil surface i n 200-nil. constant a n d were allowed to react 1 week. Tlie upper '/izone of soil then mas mixed a n d replaced i n the pots. b All pots received full-depth incorporatiom of F-free monocalciuin phosphate to supply PzOa, 160 porinds per acre.
eriiig of soil pH. The 800-puund application iiiduced the most acidic system u i the limestoned soil of this series; it repressed the growth of red clove1 considerably and imparted to it a decided increase in fluorine, which represented the largest migration of the fluorine ion from soil into a crop in this series. In series B, where the prior incorporations of limestone included the respective offsetting supplements of calcium carbonate, the taw laiger applications of hydrofluoric acid induced some repression in the growth of clover of higher fluorine contwt aiicl iiiductd lowei soil pH. On series C, where the incorporatioil oi the augnieiited charges of limestone into the upper eonr was delayed 6 days, the resultant crops and their fluorine content and soil p H values w r c inuch the same as on the limestoned systenis of series B. 1013
.
( a i that the additive fluorine ion undergoes fixation in the soil, nrhereas the chlorine ion does not ( b ) that hydrofluoric acid induced little change in final p € i on eit,her soil, in contrast to the significant lowerings that were induced by the equivalences of hydrochloric acid ( e ) that potassium fluoride caused elevations in p H on both soils, with lethal toxicity only from the 800-pound application ( d ) that the applications of potassium chloride exerted little effect upon final p H of either soil, with attendant decrease in growth on Hartsells and with increases in growth on Clarksville soil
it appears that the lethal efl' induced by the heaviest application of hydrofluoric acid was caused by high acidity, whereas the lethal effect from the equivalent application of potassium fluoride was caused by elevation in pH, which probably was initially inuch greater than the values given as finals in Table I. This probabilhPPLICATIONS O F HYDRo*%UoltICi h C I D VERSUb ZQLIVALEh I' APPLICATIONSOF HYDROCHLORIC ACID, POTASSIUM FLUORIDE, ity was indicated by the decided darkening of the soil where trhe 400- and 800-pound applicat8iorisof fluorine were made a.s pt)i,:isAND POTA~SIUX CHLORIDE.Because the growth of clover was aium fluoride. repressed by the heavy-rate applications of hydrofluoric acid 011
the unlimed Hartsells soil of Figure 1, it appeared that the repression was due either to high acidity or to thc fluoriric ion. Therefore, pot cultures of millet, in lieu of clover, were set up to provide comparisons between the effects of applications of hydrofluoric acid, hydrochloric acid, potassium fluoride, and potassium chloride solutions (as in Table II), in equivalence to fluorine a t rates of 200, 400, 800 pounds per acre surface oil soils similar to those of Table I. On Hartsells soil, the 200-youiid application of fluorine a b the slightly ionized hydrofluoric acid repressed growth of millet but that application was less repressive thau the equivalent application of the highly dissociated hydrochloric acid. The applications of hydrofluoric acid did not induce significant lowerings of hial p H values on either soil of Table 11, wheieas the hydrochloric acid caused appreciable 1oTerings on both soils. Because the fluorine ion of the applied hydrofluoric acid undergoes fixation in the soil, whereas the chlorine ion of the applications of the strong hydrochloric acid does not, the concentrations of the hydrochloric acidengendered solutes were beyond those induced by the hydrofluoric acid. These relationships may be responsible in part for the lesser toxic effect of the 200-pound application of fluorine or1 Haltsells.
On Clarksville soil, of higher calcium content, the 200-pound application of fluorine and resultant calcium fluoride proved far more repressive than the corresponding application of chlorine
DISCUSSION
The exploratory study u a5 prompted by several uncei tLiuitiw and by the hope that the firidings would serve to chart further attacks by means of pot cultureis and lysimeters. Is the immediate fertility of a soil affected by increments of atmosphere-derived bydrofluoric acid? Does the :tti:iosi)hcre-derived fluorine become fixed in the soil and there held toiaciously against uptake by vegrtation and against outgo in rain water leachings? Does a fluorine-enriched soil regain it5 natural fertility and register neai normal pH after cessatioii of atmospheric contamination? Do fluorine-enriched soils impai t a n abnormal content of fluoruic to crops grown thereon? Does the liming of a fluoride-enriched soil minimize the migratbn of the fluorine ion into forage and iutu rain water leachings? The piesent findings and those from wlatcd atudies provide answei s to some of these questions. The eff'rcts that applications of hydrogen fluoride exert upon plant grov th and upon pH, and the ameliorative effects of incoiporations of calcium carbonate, and of superphosphate, were dealt nith in a recent contribution from the S e w Jersey Station (11). A large input of fluorine carried by superphosphate, supplemented by wollar;tonite, caused no increases in fluorine content of successive crops (9), and good crops that showed normal content of fluorine resulted from incorporations of quenched calcium silicate slag that contained 2% of fluo~irie (4). The findings 01
August 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
Sherman, McHargue, and Hageman (13) indicate that the content of calcium fluoride in the slag, or calcium silicofluoride, may induce a beneficial oxidation of manganous materials native to the soil. Findings from long-time lysimeter experiments (6, 6) and from report by Agate (I), indicated that the alumino complexes of a soil hold additive fluorine ion tenaciously. The experimental conditions whereby the single applications of hydrofluoric acid supplied 100, 400, and 800 pounds of fluorine per acre may be considered, respectively, as “possible,” “improbable,” and “unthinkable” acquisitions that a field soil might acquire a s hydrofluoric acid directly from a polluted atmosphere. Even such “possible” acquisitions would be spread over a considerable period, during which the fluorine ion would become fixed (1) and would migrate but slightly into plant tops (9),or into the rain water leachings (6, 6). The pot cultures of Tables 1 and I1 were not leached before or during plant growth and, therefore, the inputs of fluorine were not diminished through drainage waters, No lysimeter data are yet available to show fluorine outgo from applications of hydrofluoric acid, but long-time experiments demonstrated that fluorine is leached only sparingly from cumulative incorporations of calcium fluoride (6, 6), the calcium content of which undergoes leaching far beyond that equivalent to the outgo of fluorine. When the atmosphere-derived acidic fluorides enter a soil that is well supplied with calcium, the immediate reaction is chiefly with that element, and the engendered calcium fluoride would be expected to act as the incorporations of that fluoride have been shown t o act (6, 6). I n marked contrast to the meager concentration of solute fluorides that inputs of calcium fluoride impart to the free water of the soil (6),without inducing measurable effect upon soil pH, inputs of calcium silicate slag impart relatively high concentrations of fluoric solutes to the rain water drainage (6) and induce elevations in soil pH. Nevertheless, substantial incorporations of the fluorine-bearing slag induced no significant increase in the uptake of fluorine by various crops (4, 9). Large inputs of calcium fluoride, and of fluorspar, did not serve as a source of nutrient calcium to plants on acidic soils, but those inputs did impart abnormal occurrences of fluorine in the decidedly subnormal crops ( 7 ) . It has been postulated that the more reactive alumino components of a soil effect a fixation of the released fluorine ion and thus decrease the capacity of those complexes to effect the fixation of the PO4 of fertilizer phosphates (10). Because the clover of the pot cultures was not exposed to an alxiormal occurrence of fluorine in the atmosphere, the fluorine content of the above-ground growth was acquired solely through the roots. I n the field, however, the occurrence of fluorine within and on clover foliage may become enhanced, possibly through stomatal intake and certainly through moist precipitations of fluoric effluents, and through deposits of mineral solids from the air a t points contiguous to those where rock phosphate is mined and processed. It appears improbable that the native fertility of a normal soil would be impaired measurably because of increments of hydrofluoric acid that might reach the soil directly from the atmosphere, a t least a t points other than those where heavy emissions occur. In time, such emissions might cause a diminution in nutrient calcium that would prove detrimental to the growing of good forage of tolerant content of fluorine. After cessation of fluoric emissions, or their abatement to a low level, subsequent vegetation on a nearby limestoned soil probably would show a normal content of fluorine. The initial objectives of the pot culture study were to ascertain the immediate effects to be expected from rain-wash increments of hydrofluoric acids on two distinctive soils, unlimed and limestoned, and in the subsequent uptake of fluorine therefrom. The duration of the early effects of additive hydrofluoric acid upon soils and upon plant composition are objectives in a followup experiment.
1803
SUMMARY AND CONCLUSIONS
Solutions of hydrofluoric acid were applied t o two representative soils in a pot culture experiment t o simulate the action of atmosphere-derived increments of that acid, and to assuie that an enhancement in the fluorine content of subsequent Crops of recfclover would be attributable solely t o the applied acid. Thc 200-ml. applications supplied fluorine a t rates of 100, 400, and 800 pounds per acre surface on both unlimed series and on the three series for each soil, variously limestoned. After 6 days, every upper 2-inch zone of soil of the 8-inch depth was niised and red clover was seeded. The 100-pound application registered slight effects upon yields, upon their fluorine content, and upon soil pH. The 400pound applications caused appreciable decrease in the growth of clover and increases in its fluorine content on the unlimed soils; but the repressions in growth and the concomitant increases in fluorine content were decidedly less pronounced on the limestoned soils. The 800-pound applications almost inhibited growth of clover on the unlimed soils, lessened it markedly on the limestoned soils, and increased appreciably the occurrence of fluorine in the subnormal crop. The larger applications of hydrofluoric acid caused lowerings of pH, except in those series where the base-rate incorporations of limestone had been augmented to offset the hydrofluoric acid additions in the upper 2inch zone. The effects of applications of fluorine and chlorine upon soils and crops were compared through use of hydrofluoric acid, hydrochloric acid, potassium fluoride, and potassium chloride in equivalent amounts a t three rates. The hydrofluoric acid. exerted little effect upon soil p H in contrast to the decided lowerings induced by hydrochloric acid; potassium fluoride caused decreases in plant growth and induced elevations in soil pH, whereas potassium chloride caused increases in plant growth and no changes in soil pH. It is concluded that the reaction of soil and its fertility will not be im aired significantly by quantities of hydrofluoric acid that woulzcome directly from the atmosphere, a t locations othrr than those close to the emissions. The present observations do not contradict previous caonclusions that a good growth of forage will not show significant increase in fluorine content through uptake from additions of solid fluorides on a soil well supplied with calcium, but the heavy inputs of hydrofluoric acid did impart an abnormal content of fluorine t o clover on the two soils used, unlimed and limestoned. The factor of ersistence of the detrimental effects of the heavy applications of Eydrofluoric acid and the extent of fluorine outgo in rain water leachings from applications of hydrofluoric arid are objectives of additional studies. LITERATURE CITED
(1) Agate, J. N., et al., “Industrial Fluorosis,” Privy Council,
Medical Research Council Memo 22, London, His Majesty’s Stationery Office, 1949. (2) Davis, H. W., “Fluorspar and Cryolite,” Report, U. S.Bureau of Mines Yearbook, p. 2, 1948. (3) MacIntire, W. H., and Associates, I s u .
[email protected].,41, 2467 (1949). (4) MacIntire, W. H., Hardin, 1,. J., Winterberg, S. H., and Hammond, J. W., Soil Sci., 50, 229 (1940). (5) MacIntire, W. H., Shaw, mr. M., and Robinson, B., Ibid., 67, 377-94 (1949). ( 6 ) MacIntire, W. H., Shaw, W. M.,Robinson, B., and Sterges. A. J., Ibid., 65, 321-39 (1948). (7) MacIntire, W. H., Winterberg, 8.H., Clements, L. B., and Dunham, H. W., Ibid., 63, 195-207 (1947). (8) MacIntire, W. H., Winterberg, S. H., Clements, L. B., Jones, EKG.CHEM.,43, 1797 (1951) L. S., and Robinson, B., IND. (9) MacIntire, W. H., Winterberg, S. H., Thompson, J. G.. and Hatcher, B. W., Ibid., 34, 1469-79 (1942). (10) Nagelschmidt, G., and Nixon, H. L., Nature, 154, 429-30 (1944). (11) Prince, A. L., Bear, F. E., Brennan, E. G., Leone, I. A, a n d Daines, R. H., Soil Sci., 67, 269-77 (1949). (12) Sappington, C. O., “Essentials of Industrial Health,” p. 2278, Philadelphia, J. B. Lippincott Go., 1943. (13) Sherman, G. D., McHargue, J. S., and Hageman, R. H., Soil S C ~56, . , 127-34 (1943). RECEIVEDOctober 26, 1950. Presented before t h e Division of Fertilizer Chemistry a t the 118th Meeting of the . ~ M E R I C A N CHEMICAL SOCIETY,C h capo, Ill.
