Organic Matter in Arkansas Bauxite
1
B!
LIGXITEAND SOILOVERBURDEX WITH FIGURE 1. MINESHOWISG TYPICAL VEGETATION A . Lignite; B. Bauxite
The bulk of organic matter in Arkansas bauxite comes from the overburden, especially from the lignitic clays. It is composed mostly of humic acids, humates, and their oxidation products. The oxidation products of these humic acids, after extraction with sodium hydroxide, may be separated into fractions insoluble in mineral acids but soluble in ethyl alcohol, soluble in acids but precipitated with aluminum hydroxide in neutral solution, and soluble in neutral solution. Analyses of the fractions separated are given where isolation was possible. Tests for specific compounds usually occurring in soils were negative. Fairly pure samples of humic acids were obtained from the lignites and analyzed. Analyses of inorganic material combined with humic acids from lignite and bauxite also are given and chemical difference is shown. A satisfactory method for the determination of organic matter in bauxite is presented.
Origin and Nature DON UTLEY A l u m i n u m Research Laboratories, N e w Kensington, Pa.
T
HE presence of organic matter in Arkansas bauxite is a matter of common knowledge to those who have mined it or used it for commercial purposes. This report represents part of the work undertaken to learn something of the behavior of this organic matter when subjected to the reagents used to treat bauxite in industrial processes. Most of this organic matter comes from the overburden. The overburdens on these deposits are composed of soil, clay, sand, ironstone, or lignite, or a combination of all five. Of the types mentioned, lignite is the only one with a high carbon content. This lignite was formed as a bog under anaerobic conditions and was laid down directly on the bauxite. The seepage of the organic matter from the lignite into the bauxite is shown in Figures 1 and 2. This impure coal of tertiary origin (3) is high in ash and sulfur, and low in fixed carbon. Pyrite is visually present and the odor of sulfur dioxide is pronounced. A typical analysis of this lignite is given in the following table. However, the lignite overburdens in contact with the bauxite are far less pure, being mixed with clay and sand. The ash on those examined ranged from 40 to 80 per cent. Moisture, %
4sh, %
Volatile matter, %
17.22 15.73 40.25
Fixed carbon, % Sulfur, yo Heat content, B. t.
U.
cerning the complex compounds found there. these compounds (7) as follows:
26.80 0.73 7470
Page classifies
1. Comparatively well-defined complex substances of known origin-carbohydrates and proteins. 2. Definitely characterized simple substances-amino acids and other organic acids, aldehydes, and bases. 3. Ill-defined substances of uncertain origin-humus.
The clayey soil above the lignite is covered with a growth of pine, oak, hickory, and gum. It is acid in nature and is not very deep. The decay of this vegetation, no doubt, has contributed organic matter to the ore deposits.
The carbohydrates and proteins, with few exceptions, do not persist long in the original state. The proteins, except scleroproteins (hair, hoof, and horn) , are rapidly broken down into amino acids and polypeptides which are built up with the carbohydrates into tissues of soil organisms. Cellulose
Soil and Lignite Organic Matter I n spite of the vast amount of work done on organic matter of soil, peat, and lignite, considerable confusion exists con35
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VOL. 30, NO. 1
is much less rapidly attacked than starches, gums, and sugars. dark red sol to a light yellow, true solution; acetic and Waxes and resins may be present for a long time unaltered. formic acids are end products of the oxidation ( 2 ) . The simple substances, such a8 amino acids and other One important property of these humic acids is their capacorganic acids, aldehydes, bases, etc., are produced from subity to neutralize or absorb bases (1). They are neutralized stances of the first class by the process outlined or are present very little by ferric hydroxide, much more by aluminum in the manure added. These simple substances form a n imhydroxide, and entirely by ferrous hydroxide. Their bufferportant link in the soil biological processes and, along with the ing action is another well-known characteristic. first group, are transient. Overburden and Bauxite Organic Fractions The third -group, - described looselv as humus, consists of dark colored amorphous substances” which are produced in Samples of overburden (clays, sands, ironstones, soils, and the soil from vegetable matter under the combined influence lignites), rocks in contact with the bauxite, and the bauxites of air and moisture. These gradually disappear by breaking were taken for examination. After being dried at 110” C., up into simpler compounds. they were pulverized to 100 mesh. Confusion also exists as to what constitutes humus, Od6n Two methods of extraction were employed. The first was (6) limited the term “humic acid” to mean that fraction of extraction in hot 5 per cent sodium hydroxide and subsethe soil alkaline extract precipitated by mineral acids and inquent precipitation with dilute sulfuric acid. The second was soluble in alcohol. I n this article “humic acid” or “humic extraction with dilute alkaline sodium acetate and precipitaacids,” which appears to be a more correct term (W), will be tion with dilute hydrochloric acid after removal of other inithat material defined by O d h . The remainder of the matepurities with various solvents. rial of humic origin will be referred to as water-soluble humus, Tests for special groups and compounds sometimes found alcohol-soluble humus, etc. in soils were made both on the original samples and on the Methods of separation from other organic material usually alkaline extracts from them. No sugars, carbohydrates, call for dispersion in dilute alkaline solution and precipitation aldehydes, aliphatic acids, proteins, purines, cyanides, isocyanides, amines, or amides were detected. Likewise tests by mineral acids (IO), previous treatment with chlorine dioxide to remove lignin (4), previous separation of mineral ( I O ) for indoles, pyrroles, and nitroso and azo compounds were matter by digestion with dilute acids, and previous separanegative. tion of waxy material by extraction with organic solvents ( 2 ) . In order to effect a clear-cut separation of organic matter from Alkaline extraction iS Open to Criticism because it oxidizes suspended inorganic matter, the bauxite and overburden samples humic acids ( 2 ) . Chlorine dioxide, a powerful oxidizing were treated with hot 5 per cent sodium hydroxide solution and allowed t o settle overnight. The solution was then carefully agent, decomposes them (8). They appear to be insoluble from the settled residue. A clay filter similar t o that i acidsl alter~them ~little ~ \iphoned organic solvents. ~ in used by Anderson and Byers (1) was not available. Any susor none at all ( 2 ) . Arnold, L w Y , and ThieNen ( 2 ) , after pended matter siphoned from the residue was of colloidal ditreatment with dilute acids, benzene, alcohol, and water, mensions or less and could not be retained on a C. S. & S. Blue Ribbon filter papei. Thi. solution was made slightly acid wlth disperse them in dilute sodium acetate solution and precipitate dilute sulfuric acid. The with hydrochloric acid. precipitated humus, after The humic acids ( 2 ) settling, was washed three times by decantation and appear to be colloids. then filtered. If m o r e They exhibit the Brownthan three decantations ian m o v e m e n t w h e n were made, the material viewed under the ultracould not be retained on A the filter. The filtered microscope. The peptizprecipitate, after b e i n g ing power of c e r t a i n sucked dry. was treated on I anions decrease in the the funnel with hot ethyl following order: OH- > alcohol until the extracts c0,-- > C K - > became yellow. The material extracted with alcoC2H302- > CzO4-> hol was r e c o v e r e d by Sod-- > C1- > NOS-. distillation of the main The series for inducing portion of the solvent and evaporation of the rest on coagulation are Ba++ > a water bath. The filtrate Ca++ > H + > K+ > from the first decantation Na+. They are peptized of the sulfuric acid precipireadily by aqueous ortation, if colored, was ganic solvents, such as I made neutral with sodium hydroxide to precipitate alcohol, a c e t o n e , and the mineral matter. A pyridine. I n the cataFIGURE2. MINESHOWING LIGNITEOVERBURDEW note was made if organic phoresic cell humic acid A . Lignite; B . Bauxite c o 1 o r precipitated with sols move towards the it. Although direct extraction with sodium hydroxide oxidizes positive electrode in acid, neutral, and basic solutions. some organic matter and disperses colloidal clay, it was thought composit~onof humic acid prepsWaksman states that advisable to make such an extraction, since an alkaline digestion with caustic 1s used in certain commercial processes. Sulfuric rations varies (11). The carbon content USUallY ranges acid was used for precipitation since sulfides, sulfites, and SUIfrom 52 to 56 per cent and may be as high as 58 per cent. Xitrogen and sulfur, both of which are present, are considered fates Theare material normally precipitated present in by theacid materials and insoluble examined.in alcohol by some investigators as impurities; others believe that they possibly is composed of humic acids with are essential constituents ( 2 ) . Using a quinhydrone ekesilicate or hydrous oxides. The alcohol-soluble fraction appears to be pure organic material. The organic matter precipitated trode, Arnold et al. found the average pH of several sols of with aluminum, titanium, and iron hydroxldes m neutral solution humic acids to be 3.8 (a). The acids are oxidized readily by is humic in nature and is possibly combined with the inorganic nitric acid at room temperature. They disperse in strong elements ( I O ) . No n-ay was found t o separate this organic matsulfuric acid and reprecipitate again on dilution. Oxidation ter from the morganic, and no way was found t o isolate the acidsoluble organic material. is rapid in alkaline solution. Oxidizing agents convert the
i
I
JANUARY, 1938
INDUSTRIAL AXD ENGINEERING CHEMISTRY
31
a t about pH 8.0. This experiment was repeated using humic acids from bauxite. I n this case the indicator substance was bright red. On addition of aluminum sulfate it was precipitated with aluminum hydroxide when neutralized with sodium hydroxide. This reaction took place to a lesser extent when humic acids were treated with hydrogen peroxide in neutral solution, but no oxidation took place in acid solution. An appreciable amount of alcohol-soluble material was found in the residues from the alkaline and neutral oxidation experiments. Since formic and acetic acids are end products of humic acid oxidation, tests for these compounds were made. None were found in any of the fractions examined. Prolonged hot oxidation in sodium hydroxide solution with hydrogen peroxide of the humic acids FROM TABLEI. PERCEXTAGE ANALYSISO F HCMIC-4CIDS EXTRACTED LIGNITE WITH SODIUM HYDROXIDE AND PRECIPITATED WITH SULFURIC ACID and alcohol-soluble humus produced oxidation Sample -Ash -&na]ysis--Organic f i n a l y s i ~ products that, upon acidification and distillation SO. Source .ish Si02 R103 Total Carbon Nitrogen with steam, gave tests for both acetic and formic 1 Humic acids from ligacids. nite 37 46.88 46.20 50.14 96.34 45.03 0 40 2 Humic 55.11 37.92 93.03 43.34 1.51 Analysis showed that the inorganic material in nite 39acids from lig- 68.31 3 Humic acids from ligthe humic acids from the lignites was mostly 61.76 49.49 44.24 93.73 46.59 1 09 nite 45 ferrous iron and aluminum silicate. In the humic 4 Alcohol-sol. humus from bauxite (composite) 13.51 ... ... ... 47.65 1.03 acids from the bauxites the combination was 5 Alcohol-sol. humus from lignite (composite) 9.41 . .. ... .,. 47.76 0.40 alumina, ferric iron, ferrous iron, and silica. Digestion under pressure a t 1.50" C. with sodium hydroxide (102 grams sodium hydroxide per liter) peared into the alcohol-soluble portion. The ash in the of three bauxites previously treated with hot dilute caustic, humic acids from the lignites was high and essentially alumiextracted slightly more color. However, the bulk of the num silicate. Repurification failed t o lower this ash content. extractable organic matter was removed by double extraction Likewise, some of the organic material was made soluble in with hot 5 per cent sodium hydroxide. alcohol on repurification. Although a trace of organic mateColor comparison showed that there is a distinct difference rial was present in all colorless extracts examined, the amount in humic extractions with sodium hydroxide from bauxites was infinitesimal and no organic groups were identified. and lignites. The colors of the lignite extracts ranged from The distribution of organic matter extracted from some black to brown; in the bauxite extracts the colors ranged of the samples is given in Table 11. from dark red to yellow. Since the colors could not be One sample deserves special mention-an iron phosphate matched by dilution, this difference was something more rock in contact with the bauxite in a surface mine where the than a matter of concentration. overburden was a thin soil. A sodium hydroxide extract of this rock was bright red. Very little material was precipitated upon addition of dilute sulfuric acid. The soluble TABLE11. DISTRIBUTION OF ORGANIC COLORIN SODIUM material was yellow in acid solution and red in alkaline, OF SAMPLES HYDROXIDE EXTRACT changing at about p H 8.0. This red color was adsorbed and -Sol. in HI SO^Adsorbed precipitated with aluminum hydroxide at the neutral point. by -Insol. in HzSOrIf sufficient aluminum was present, the filtered solution was .41101 in Sol. in Sample 1-01. in Sol. in neutral neutral yellow in both acids and alkalies. Bauxite from the same area No. Description alcohol alcohol soln. soln. exhibited this phenomenon to a lesser extent. Extractions 34 Bauxite (dark oolites) Trace $ Trace 35 Bauxite (dark oolites) from bauxite of other areas, using larger amounts of material, 36 Oolitic bauxite Trace + revealed the same phenomenon. + Trace 37 Lignitic clay +7+ Trace 39 Ljgnjtjc clay -Extracts from the lignites gave no acid-soluble organic 45 Ligrutic clay $$$ Trace 48 Iron phosphate Trace + ++ ++ color. The organic color in the extracts from the bauxites 50 Bauxite and clays is distributed between the acid-soluble and the 51 Bauxite + + ++ 52 Bauxite + + acid-insoluble. The lignite and the bauxite in contact with it contain a high concentration of sulfurous acid, due to the oxidation of This suggests a difference in the nature of mineral and the pyrite present. The absence of the acid-soluble organic matter in the lignite is possibly due to the highly acid conlignite humus. That there is a difference in organic-inordition of the lignite plus the presence of the sulfur dioxide; ganic tie-up will be shown. Other possible differences are the soluble portion has seeped into the more basic bauxite degree of oxidation and relation of nitrogen and sulfur to rest below. of molecule. Oxidation of humic acids with hydrogen peroxide The presence of the acid-soluble organic matter in extracts in alkaline solution and acidification of treated solution yielded from the bauxite and its absence in the extracts from the a humus precipitate lighter in shade than the original humic lignite, where sulfurous acid is always present, suggests that acids. these colored soluble compounds might be oxidation prodI n an attempt to get humic fractions with less ash content, ucts of humic acids. A sample of humic acids from lignite the bauxite and lignite samples were treated by a method was boiled for several minutes with hydrogen peroxide in similar to the one used by Arnold to obtain pure humic alkaline solution. The solution was made acid and the acids from peat (2). Preliminary investigation showed that insoluble material filtered off. The acid filtrate was yellow the humic acids from the bauxites and lignites would not disperse readily in neutral sodium acetate solution but would and turned reddish brown when made alkaline. The color change, as was the case with the phosphate rock, took place in slightly alkaline solution. Therefore, the treatment was
Analyses of the humic fractions from lignitic overburdens and bauxites are given in Table I. Organic analysis is on an ash-free basis. A true figure for carbon and nitrogen could not be obtained on samples 1 , 2 ,and 3 because of the unknown amount of water combined with the high ash of these samples. A large amount of bauxite was handled to obtain the small amount of organic material. Most of the recoverable organic matter from the bauxite showed in the alcohol-soluble fraction. With the exception of lignite sample 1, the humus precipitates from lignites contained practically no alcoholsoluble portion. When attempts a t repurification of alcoholinsoluble humus from bauxites were made, most of it disap-
+
+
:
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VOL. 30, NO. 1
modified accordingly. The scheme used is outlined in cipitation with hydrochloric acid and washing by decantation, Figure 3. the atered precipitate was treated with hot alcohol to remove A higher concentration of hydrochloric acid was used in alcohol-soluble humus. The alcoholic extract was added to the removal of mineral matter from the bauxites than from that from the original sample, and the composited material the lignites, and double extraction was employed. The ions was recovered by distillation and evaporation of the alcohol. found in the acid solution were Al+++,Fe++, Fe+++, and These samples and the humic acids were dried at llO°C. and SO4--. No carbohydrates or sugars were found. After preanalyzed. Analyses are given in Table 111. Organic analycipitation of inorganic cations, this extract was usually colorsis is on an ash-free basis. less but sometimes pale yellow. A small amount of organic matter of some sort was always present. A large amount of yellow or orange waxy TABLE 111. PERCEXTAGE ANALYSISO F PURIFIED HUMIC FRACTIONS Fraction material was found in the benzene extract from NO. Description Ash Carbon Nitrogen Sulfur the lignites. A trace of this substance was al1 Lignite humic acids from No. 37 11.91 57.22 0.60 3.52 ways present in the benzene extracts from the 2 Lignite humic acids from No. 39 14.69 55.85 1.19 1.21 3 Lignite humic acids from No. 45 14.24 54.13 1.99 2.92 bauxites. I n the lignites it ranged from 0.2 to 4 Bauxite humic acids (composite) 47.53 45.26 0.85 1.39 0.75 per cent of the original sample; in the bauxites 5 Lignite alcohol-sol. humus (composite) 2.62 48.37 0.29 3.59 it amounted to about 0.01 per cent. This wax had a melting point identical with that of montan wax which is commonly found in the benzene extract from lignite The carbon figures for the low-ash materials vary in the range given by Waksman for humic acids (11) and approach ( 5 ) . Montan wax has a melting point range of 73" t o 84" C., depending on the source. It oc;;rs in pea&, brown coal, bitu58 per cent. The nitrogen and sulfur are generally believed minous shale, and lignite. Crude montan wax from lignite is to be in organic combination. The lower carbon figure on the humic acids from the bauxite, and the higher ash indiusually broxnish to black in color. The wax from the lignite cates a difference in structure of humic acids from bauxite examined here was yellow or orange and resembled beeswax. and lignite. Direct extraction with benzene yielded a dark-colored wax. The combined effect of the hydrochloric acid used and the sulfur dioxide in the lignite possibly bleached this wax. From 0.2 to 0.7 per cent organic matter was extracted TABLEIV. DISTRIBUTION OF ORGASICCOLOR 15 SOLVENTB from the lignite with hot alcohol. Very little was extracted Sol. in Sol. in Sol. in Sol. i n BenAlco- Sol. in NaAc + Sample from the bauxite. No tannins or alkaloids were found. The KO. Description HC1 zene hol Water KaOH organic matter extracted appeared to be of a humic nature. 34 Bauxite (dark KO sugars, tannins, or proteins were found in the water + oolites) Trace Trace Trace 35 Bauxite (dark extract. oolites) Trace Trace + 36 Oolitic bauxite Trace Trace + The bulk of the extractable organic material was removed 37 Lignitic clay Trace Orange + - f++ TWO.. by extraction with alkaline sodium acetate and appeared 39 Lignitic clay Ye&w + to be humic acids. In order to lessen oxidation, the alkaline wax 45 Lignitic clay Trace Ye&w f extracts were removed from contact with the samples as soon Wax as the suspended matter settled. They were then filtered on 48 Iron phosphate + Trace Trace Trace t+ 50 Bauxite Trace Trace ++ a Buchner funnel through double C. S. & S.White Ribbon Trace Trace ++ 51 Bauxite Trace Trace ++ 52 Bauxite papers, and made acid with hydrochloric acid. After preI T Un
Pulverized sample (Lignites refluxed with
2.i ZCl,
bauxites with IC$ ECl) F i l t r a t e (metallic,ions,. hydrolytlc proaucts)
(Refluxed with benzene) F i l t r a t e (vaxes, f a t s m a resinsj
on ine evaporeted, & i k d 1dlb"C.
(Refluxed with 9% alcohol)
F i l t r a t e (tannins .alkal o i d s Ligher elcohAls d c o hol-soluile humic compounds
(Refluxed with water)
NaOH
(Extracted with
+
1% N&c)
F i l t r a t e ( - w a r s , tannins pectins proteiAs, water-shuble humic compounds
( F i l t e r e d on Beuc'mer funnel using double C.S. & S. Vinite Ribbon paper)
Ty
d e b o d y material,
( l i g n i n , etc'., (Discarded)
Z r e c i D i t a t e jhuvic coupounasJ
F i l t r a t e ( h m i c compoundsi
7 (AJded SCl)
F i l t r a t e (humic compoundsj
I
(Treated with hot alcohol) (humic acids) (Dried a t 110'C.)
FIGURE 3. MODIFIEDARNOLDMETHODFOR EXTRACTION OF HUMIC ACIDSFROM BAUXITE AND LIGNITE
+++ +++
To make certain that the mineral matter found in the humic acid fraction from bauxites was not due to occlusion, this sample was repurified by the same procedure used in obtaining the original humic acids. Sample 4 is the repurified fraction. The ash content was reduced approximately 5 per cent by this treatment, and some of the organic matter was made soluble by the alkaline treatment. That this organic-inorganic tie-up is a t least a close physico-chemical relation, if not a direct chemical combination, is evident. The humic acids of the lignites seem to be of the free acid type; the humic acids of the bauxites are combined as humates. The distribution of organic color in the various solvents used for purification is given in Table IV. The modified Arnold method of purification was used. A spectrogram was made of this ash and of a composite of the ash from the humic acids of the lignites. The following elements are present: Composite of Ash from Lignite Hurmc Acids Significant Mino? amounts impurities Calcium Aluminum Chromium Silicon Copper Sodium Gallium Titanium Magnesium Iron Tin Zirconium Manganese Molybdenum Boron
Ash of Composited Bauxite Humic Acids Significant Minor, impurities amounts Calcium Aluminum Chromium Iron Sodium Silicon Molybdenum Titanium Gallium Manganese Magnesium Tin
INDUSTRIAL AND ENGINEERING CHEMISTRY
JANUARY. 1938
Spectrographic traces of impurities are not listed. AU of these elements, with the possible exception of boron, have been detected by the spectrograph in Arkansas bauxite. No spectrographic analysis of the lignite is available. The high sodium content is due t o the occluded sodium chloride from the reagents used. Partial analysis of the ash is given in the following table; aluminum oxide and aluminum silicate predominate in the ash from the lignite humic acids, whereas aluminum oxide is the predominating material in the a h from the bauxite humic acids. Iron oxide, titanium oxide. and silica occur in the latter in about equal amounts: Corn mite Aeh of of A e ~ f r o r nCompmtted Lianite Baurite Hurn~o Humic Acids Adds
Sios
Ti02 MnO
30.9
11.3 2.5 5.0
..
44.4
18.7 18.2 16.4 0.6
Corn mite
Ash of
Lignite
Bauxite Humic Adds
oi Asgfrom Cornposited Iiuumie Aoids
2x0.
MoOi NaCI
Total
1.5
0.6
44.2
96.0
.. .. .. -
98.3
Digestion of the humic acids from bauxite with 1 to 5 sulfuric acid and titration of the filtered solutions with potassium dichromate indicated that the sample contained at lesst 4.5 per cent ferrous iron (calculated as ferrous oxide). Heretofore, it was thought that the only ferrous iron in bauxite soluble in dilute acids occurred as siderite. The bulk of the organic matter extracted was found in the sodium acetate extract. This material, when precipitated with hydrochloric acid, was distributed through acid-insoluble, alcoholaoluble, and acid-soluble in the same order as by direct alkaline extraction.
Determination of Organic Matter Color comparison has proved unsatisfactory as a method for the determination of organic matter in bauxite. Prelimimary treatment with dilute sulfuric acid to remove carbonatea, and subsequent combustion, seems to be the best method. An arbitrary ratio of carbon to organic matter must be taken. The foregoing work indicates that the organic matter in bauxite is approximately 50 per cent carbon. The most satisfactory method for the determination of organic matter in bauxite seems to be oxidation, using sulfuric and chromic acids according to Scott (9). Organic matter determinations on blended metal grade Arkansas bauxite over a period of 6 months ranged from 0.34 to 0.43 per cent.
Summary 1. Most of the organic matter in bauxite comes from the
overlying lignite and is humic in nature. 2. The humio acids extracted range in composition from 52 to 56 per cent carbon. Nitrogen and sulfur also are present. They are dispersed in alkaline solution and precipi-
39
tated by dilute mineral acids. Oxidation is rapid in alhsline solution; carbon dioxide, formic, and acetic acids are formed as end products. They adsorb bases and act as buffers. 3. Special tests for sugars, earbohydratea, aldehydes, simple organic acids, indoles, pyrroles, for nitroso, purine, and azo compounds, and far cyanides, isooyanides, amines, and amides, were negative. 4. Direct alkaline extraction and precipitation with dilute sulfuric acid showed that bauxite organic matter can be separated into fractions insoluble in acid and in alcohol, insoluble in acids but soluble in alcohol, soluble in acids hut precipitated with alumina in neutral solution, and soluble in neutral solution. All appear to be oxidation products of the humic acids. 5. Preliminary purification of samples with hydrochloric acid, benzene, alcohol, and water, before dispersion in alklkaline sodium acetate, indicated that most of the organic matter is of the humic acid type. The fractions from the lignites have a normal carbon content; those from the bauxites are somewhat lower and are combined with a quantity of inorganic material, posyibly as inorganic humates. 6. A spectrographic and chemical analysis of the ash reveals that the predominating inorganic material from the lignites is aluminum silicate and aluminum oxide, and from the bauxit.es, aluminum oxide. 7. Color comparison is unsatisfactory for determination of organic matter. The wet combustion method appears to he the most satisfactory. The organic matter in Arkansss bauxite is normally 0.3 t.o 0.4 per cent.
Acknowledgment The writer wishes to thank R. C. Cross and his staff of The Republic Mining and Manufacturing Company, and also the Spectrograph Department of the Aluminum Research Laboratories for their assistance in this investigation. The helpful criticism and encouragement given by IT. V. Churchill, J. D. Edwards, R. B. Derr, and F. C. fiary of the Aluminum Research Laboratories are greatly appreciated.
Literature Cited (1) Andereon, M , S..and Byerrs, H. G., U. 8. Dept. Asp., Bdl. 377 (1933). (2) h o l d , C. L.. Low, A.. and Thiesaen, R., U. S. Bur. Mines, Kept. Inae8tiyolim 3258 (1934). (3) Branner, J. C.,Ark. Geol. Survey, Ann. R e s . , 2, Ch. V (1892). (4) Johnuon, E. C.. dissertation. Univ. Pittsburgh, 1930. (5) Mellon, I., Chem. IndzLstries. Dee.. 1935. (6) OdOn, Sven, KoLZoidchnn. Beiheffe,11, 75-260 (1919). (7) Page, 1%.J., Trona. Faraday Soc., 17, paFt 2,see. 3 (1922). (8) Schmidt, Eric. and Atterer. Matthais, B e . , WB, 16714 (1927). (9) Scott, W. W.,"Standard Methods of Chemical Analysis," Vol. 1, New York, D. Van Nostrsnd Co.. 1929. (10) Shorey, E. C.,U. 8. De@. Agr., Bull. 211 (1930). (11) Waksman, 8.A,, J . Chem. Educutia. 12,No. 11 (Nov.. 1935). Rscsmrmo July 8. 1937.
