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in t h e chlorination washings, these constants are not t o be regarded as proximate constituents but rather as radicals connected with t h e constituents cellulose and lignin. With t h e exception noted, these constants may be ignored in t h e summative analysis of coniferous woods. SUMMARY
I-A study is made of t h e distribution of t h e groups contained i n redwood which yield furfural, acetic acid, and methoxy, with t h e object of learning their relation t o t h e constituents cellulose and lignin. 11-About half of t h e furfural-yielding groups are associated with t h e cellulose, b u t only a small amount with t h e lignin. T h e portion present as true pentosan is hydrolyzed and removed during chlorination. 111-The acetic-yielding groups are partly associated with t h e cellulose, much less so with t h e lignin. A small amount appears t o be detached from either. T h e results are not conclusive in view of t h e small amount present i n redwood a n d t h e analytical difficulties. I n t h e case of coniferous woods acetic acid probably need not be considered as a proximate group. IV-The methoxy groups are wholly associated with t h e lignin. They may be partially split off from it b y acid hydrolysis. V-In t h e summative analysis of coniferous woods, all of t h e acetic-yielding and methoxy groups a n d part of t h e furfural-yielding groups may be disregarded as already accounted for in t h e cellulose and lignin. T h e furfural-yielding substances contained in t h e chlorination washings and representing hydrolyzed pentosans should be estimated. THE PROXIMATE ANALYSIS OF CONIFEROUS WOODS By W. H. Dore DIVISIONOB AGRICULTURALCHEMISTRY, U N I V E R S I T Y OF CALIFORNIA AGRICULTURAL EXPERIMENT STATION, BERKELEY,CAL Received November 18, 1919 INTRODUCTORY
A method has been recently proposed b y t h e author for t h e summative proximate analysis of woods.l.* Later investigations have shown t h e advisability of certain modifications of t h e original scheme which are considered in detail in this paper. T h e proposed system for t h e analysis of wood effected a separation of t h e wood substance into t h e fol!owing fractions: loss on drying, benzene extract, alcohol extract, water-soluble, soluble in one per cent sodium hydroxide, cellulose, and lignin. Full information as t o t h e composition of these fractions was lacking, b u t it was believed t h a t t h e wood constituents were separated into logical groups based upon chemical similarity and economic value. T h e scheme was found t o account for nearly all of t h e material of coniferous woods i n t h a t t h e sum of all constituents varied from 96 t o 97 per cent for the three conifers examined. With t h e hardwoods t h e method was unsuccessful, as I O t o 1 7 per cent of t h e constituents remained unaccounted for. T h e available d a t a seem t o indicate t h a t t h e chemistry of t h e hardwoods is an entirely separate problem. The woods of t h e broad-leaved trees have accordingly been omitted
* Numbers refer to Reference, page 479.
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from consideration in this investigation and t h e conclusions are applicable t o t h e conifers only. DEFECTS I N P R O P O S E D SCHEME ( I ) ITS F A I L U R E TO G I V E C O R R E C T R E S U L T S F O R C E L L U -
was noted in t h e original p a e e r l t h a t when digestion in one per cent sodium hydroxide was used less cellulose and lignin were obtained t h a n when this treatment was omitted. I n a subsequent paper2 it was shown t h a t t h e diminished yield of cellulose was due t o partial destruction of true cellulose instead of to greater purity of t h e product. Accordingly t h e results for cellulose are incorrect. No direct d a t a are available for lignin, b u t i t has been shown in t h e preceding paper t h a t lignin readily loses a portion of its methoxy groups when it undergoes acid hydrolysis. Possibly t h e s a m e effect is produced b y alkalies. ( 2 ) T H E V A G U E S I G N I F I C A N C E O F T H E WATER-SOLUBLE A N D ALKALI-SOLUBLE FRACTIONS-In t h e absence Of detailed studies of t h e substances contained in these portions, it was believed t h a t t h e y consisted of substances corresponding approximately t o Konig’s “proto” a n d “hemi” forms of cellulose and lignins3 It is apparent from subsequent studies,2 however, t h a t they contain also degradation or hydrolytic products of t r u e cellulose and true lignin. T h e numerical expression of these fractions has therefore no value as a n analytical statement of wood constituents. L O S E A N D LrGNIN-It
(3)
THE F A I L U R E T O EXPRESS THE HEMICELLULOSES-
Schorger’s studies of mannan4 and galactan6 have shown t h a t these carbohydrates a r e Eound in all conifers, sometimes in considerable quantity. Xylan is well known as a constituent of woods. It is therefore evident t h a t a complete analysis of a wood should t a k e these hemicelluloses into consideration. I n t h e proposed scheme t h e water- and alkali-soluble portions only partially accounted for these bodies together with other substances. (4) O R G A N I C RADICALS-The original scheme took no account of organic radicals present-the so-called “wood constants.” T h e preceding paper has shown t h a t , with t h e exception of t h e furfural-yielding substapces soluble in t h e chlorination washings, these radicals may be disregarded as proximate constituents of coniferous woods.6 T h e original scheme is defective, however, in t h a t i t ignores this soluble furfural-yielding substance. T h e remedies for t h e above defects are quite evident. T h e cellulose and lignin determinations should b e made reliable b y omission of t h e alkaline hydrolysis. T h e water- and alkali-soluble fractions would disappear, leaving the hemicelluloses entirely unaccounted for. It would then be necessary t o give t h e hemicelluloses a separate place in t h e scheme, and methods would be required for their estimation either collectively or individually. T h e soluble furfural-yielding substance (probably t h e pentosan, xylan) would be included in t h e hemicelluloses. T h e present investigation is an a t t e m p t t o revise t h e original scheme in accordance with t h e above suggestions. Methods have been applied for t h e determination of t h e hemicelluloses. The revised procedure has then been checked by making these and
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t h e other determinations required for a complete summative analysis on t h e three coniferous woods formerly employed. EXPERIMENTAL
T h e woods examined were redwood ( S e q u o i a s e m p e r v i r e n s ) , yellow pine (Pinus p o n d e r o s a ) , and sugar pine (Pinus l a m b e r t i a n a ) . T h e original material was in t h e form of slabs. I n t h e case of t h e redwood it represented mostly sapwood with a small amount of t h e outer portion of heartwood. I n t h e case of t h e pines it represented sapwood only. T h e samples were in t h e form of fine sawdust obtained b y making a number of cross-sectional cuts of t h e slabs and screening t h e resultant material through a sieve having 50 meshes t o t h e linear inch. As considerable coarse material was rejected, t h e samples cannot be regarded as strictly representative of t h e original material. T h a t , however, is of no importance t o t h e purpose of this s t u d y which was t o determine t h e applicability of t h e analytical methods t o t h e woods employed. ANALYTICAL METHODS
DRYING-TWO grams of t h e wood were dried at 100' C. t o constant weight. B E N Z E K E EXTRACT-TWO grams of material dried as above were placed in an alundum thimble and extracted in a Soxhlet apparatus for 6 hrs. with benzene. T h e solvent was t h e n evaporated and t h e residual extract dried for I hr. a t 1 0 0 ' C., and weighed. A L C O H O L EXTRACT-The residue from t h e above treatment was extracted for 6 hrs. with 95 per cent alcohol. T h e solvent was evaporated and t h e residue dried and weighed as before. CELLULOSE-TWO grams of material after extraction with benzene and alcohol as above were transferred t o a Gooch crucible containing a cloth filtering disk and washed with distilled water. T h e cellulose was determined by t h e Sieber and Walter method as described i n t h e preceding paper and elsewhere.' T h e residues were tested for lignin b y digestion i n 7 2 per cent sulfuric acid and when appreciable amounts were found, t h e lignin was filtered off and weighed, and t h e cellulose corrected for it. LIGNIN-TWOgrams of material after extraction with benzene and alcohol were air-dried a t low temperature (60' C.) and transferred t o a 750 cc. flask. 2 0 cc. of 7 2 per cent sulfuric acid were added and t h e mixture allowed t o s t a n d a t room temperature for 3.5 hrs. 5 0 cc. of cold water were added, then 5 0 0 cc. of hot water. T h e residue was filtered off on a tared Gooch crucible, washed thoroughly with hot water, dried, and weighed. HEMICELLULOSES-The hemicelluloses are apparently contained quantitatively in t h e chlorination washings,2 and it was thought at first t h a t these solutions might be utilized for their determination. They were found t o be unsatisfactory for this purpose except i n t h e case of t h e soluble pentosans. The presence of lignin derivatives interferes seriously with either t h e collective estimation of t h e hemicelluloses b y reducing sugar methods or t h e separate mannan and galactan determinations. LOSS ON
477
S O L U B L E PENTOSANS-The chlorination filtrates and washings from four cellulose determinations representing 8 g. of original material were evaporated t o a little less t h a n 500 cc., transferred t o a 5 0 0 cc. volumetric flask and made up t o volume. Aliquot parts of 1 2 j cc. each were placed i n t h e distilling flask of t h e pentosan apparatus, 30 cc. of concentrated hydrochloric acid added, and t h e furfural distilled off in t h e usual manner. T h e furEural was precipitated as phloroglucide, and t h e precipitate filtered off, washed, dried, and weighed. T h e results were calculated t o xylan by means of Krober's tables. SIANNAN-The method used was t h a t described b y Schorger.8 Ten grams of t h e wood were hydrolyzed b y boiling for 3.5 hrs. with 150 cc. of hydrochloric acid (sp. gr. 1.025) in an Erlenmeyer flask under a reflux condenser. T h e mixture was then filtered and t h e residue rinsed into a beaker and digested with I O O cc. of water for a few minutes on t h e hot plate. T h e solution was poured through t h e filter and t h e residue again rinsed back into t h e beaker and t h e digestion repeated. This process was continued until about 500 cc. of filtrate were obtained. The filtrate was neutralized with sodium hydroxide and t h e solution made slightly acid with acetic acid, after which it was evaporated t o 1 5 0 cc. It was filtered into a glass-stoppered Erlenmeyer flask, and a mixture of I O cc. of phenylhydrazine and 2 0 cc. of water acidified with glacial acetic acid was added. T h e mannose hydrazone was in every case immediately precipitated. T h e whole was allowed t o stand for 2 hrs. with frequent shaking and then filtered on a Gooch crucible fitted with a filtering disk of mercerized cotton cloth. It was washed several times with cold water a n d then with acetone, dried a t 100' C. and weighed. T h e weight of residue was calculated t o mannan by multiplying by t h e factor 0.6. GALACTAN-Five grams of t h e material were placed in a I O O cc. beaker, and 60 cc. of nitric acid (sp. gr. 1.15) were added. The beaker was placed in a water b a t h and t h e liquid evaporated t o about 2 0 cc., care being taken not t o allow t h e temperature of t h e water b a t h t o exceed 8 7' C. T h e mixture was then diluted t o about 7 5 cc. with hot water, and filtered. T h e residual cellulose was washed until t h e filtrate came through practically colorless. A total volume of about 250 cc. was generally t h u s obtained. T h e filtrate and washings were evaporated on t h e water b a t h a t 87' C. t o a volume of about I O cc. T h e residue was set aside for several days t o allow t h e mucic acid t o separate out. Large crystals (possibly oxalic acid) always formed a t first, t h e n a d a y or two later fine flakes of mucic acid separated out. At this point t h e mixture was stirred vigorously t o facilitate t h e precipitation. About 2 4 hrs. after t h e mucic acid appeared t h e mixture was diluted with 2 0 cc. of cold water. T h e larger crystals redissolved leaving t h e mucic acid unaffected. After a further 2 4 hrs. standing, t h e mucic acid was filtered off on a tared asbestos Gooch crucible and washed with about 50 cc. of water, 60 cc. of alcohol, and several times with ether. It was then dried a t 100' C. for 5 hrs. and weighed. Galactan was calculated b y multiplying t h e weight of residue b y t h e factor 1.2.
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By t h e foregoing methods t h e following results were obtained for t h e three coniferous woods examined. T h e figures are i n every case averages of two or more determinations. I n t h e first three columns are given t h e results on air-dry material as found by analysis; in t h e second three, t h e same results are recalculated t o t h e oven-dry basis. ANALYSESOF W O O D S (Results in Percentages) - . -AIR -DRYBASIS-OVEN-DRY BASIS1 SAMPLE No.. . . . . . . . . . 2 3 1 2 3 RedYellow Sugar Red- Yellow Sugar Pine Pine wood wood Pine Pine 8.98 9.84 Loss on drying at 100 C. 11.62 ............ Benzene extract., ...... 2.02 2.56 0.30 0.34 2.22 2.84 3.88 1.36 1.71 Alcohol extract.. 4.39 1.49 1.90 CellFlose . . . . . . . . . . . . . . 48.51 52.54 53.36 54.89 57.72 59.18 30.49 26.82 26.60 Lignin. 34.50 29.47 29.50 Soluble oentosans (as
....... ...............
3.18 1.68 5.80 5.98 0.71 0.45 32 101.41 102.18
3.67 3.49 1.86 3.21 6.37 6.63 0.50 0.78 0.50 101.50 101.54 102.41
D I S C U S S I O N OF METHODS
CELLuLosE-It has been previously shown t h a t t h e method here practiced (omission of preliminary hydrolysis) gives t h e maximum yield of cellulose free from hemicelluloses and lignin. The process therefore conforms t o t h e requirements of an accurate cellulose method and t h e product t o t h e proposed definition of a t r u e cellulose derived from lignified material.2 LIGNIN-The term “lignin” has not yet been defined with sufficient precision t o permit a comparison of t h e product with exact specifications. Lignin is generally understood t o denote t h e non-cellulose portion of t h e wood tissue proper and this conception implies its freedom from extractives, hemicelluloses, and cellulose. T h e most accurate method for lignin is therefore t h e one t h a t yields t h e greatest amount of t h e substance with t h e highest purity according t o t h e above standards. It is believed t h a t there is sufficient evidence t o justify t h e claim t h a t t h e method used conforms t o these requirements. Both acid and alkaline hydrolysis result in diminished yield of product and i t has been shown t h a t this is due ( a t least i n t h e former case) t o a partial splitting off of t h e methoxy groups which are characteristic portions of t h e lignin complex. Accordingly, only by t h e complete omission of hydrolysis is t h e full yield of lignin obtainable. Inasmuch as t h e lignin disappears completely on being submitted t o t h e alternate action of chlorine gas and sodium sulfite solution, i t is free from cellulose which would otherwise remain as a residue. On hydrolyzing with 2. j per cent sulfuric acid no reducing sugars were obtained, so t h e material is free from hemicelluloses. T h e preliminary treatment with benzene and alcohol precludes t h e possibility of t h e presence of extractives. T h e residue may be therefore considered “pure” in accordance with t h e requirements outlined. S O L U B L E PENTOSANS-Dilute alkaline solutions have been recommended for extracting xylan or wood gum from t h e hard woods.9 I t has been asserted, however, t h a t t h e wood gum of coniferous woods is much less readily soluble in alkaline solvents t h a n t h a t from t h e wood of t h e broad-leaved trees.1° For this reason i t
Val.
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NO. j
appeared t o be desirable t o use t h e chlorination liquors for t h e determination of soluble pentosans. MANNAIi-The method gave results t h a t were i n good agreement with each other and consistent with those given b y Schorger” for t h e corresponding woods. Small portions of t h e residue, recrystallized by alcohol, gave a melting point of 188’ C. GALACTAN-In their paper on t h e galactan of the western larch, Schorger and Smith12 report only traces of soluble galactans in t h e coniferous woods examined. I n their experiments I O O g. of t h e material were digested several times in hot water and t h e resulting solution evaporated nearly t o dryness and treated with nitric acid in t h e usual manner. Other investigators,13 however, have reported t h e presence of galactan in sulfite waste liquors, indicating t h a t galactans are contained in some of t h e paper-making woods. It therefore seemed probable t h a t galactans are present in not readily soluble form. Accordingly no a t t e m p t was made in t h e present investigation t o extract t h e galact a n as such from t h e wood by means of solvents. Instead t h e procedure of attacking t h e wood directly with nitric acid was decided upon as t h e best means of giving t h e full galactan content of t h e wood. T h e evaporation of t h e wood substance with nitric acid results in t h e production of a large amount of insoluble oxycellulose which interferes with t h e separation of t h e mucic acid. This difficulty was overcome by t h e procedure devised by Miyake14 in which t h e mixture, after evaporation, is diluted, and t h e solution containing t h e mucic acid is filtered off from t h e insoluble matter and again evaporated. T h e author has pointed o u t t h e uncertainty of yield of mucic acid by t h e usual process when only small amounts of galactan are present.15 Schorger and SmithlG have shown t h a t much better results are obtained if t h e temperature is not allowed a t a n y time t o exceed 87’ C., instead of maintaining t h e b a t h a t 94’ t o 96’ C., as prescribed in t h e official method for galactan.17 T h e use of the lower temperature has accordingly been adopted. Considerable difficulty was encountered a t first in obtaining a crystallization of t h e mucic acid after evaporation. This appeared t o be due chiefly t o t h e interfering action of oxalic acid or other substances contained in t h e solution. When t h e latter was evaporated t o t h e usual volume of 2 0 cc., no separation of mucic acid occurred even after several days’ standing. By evaporating t o a smaller bulk clear crystals separated out after one or two days. These crystals on standing increased in size and a d a y or two later t h e characteristic mucic acid flakes were precipitated. After t h e last precipitation was judged t o be complete, t h e larger crystals were easily removed by diluting t h e solution t o t h e usual volume of 30 cc. T h e amounts of residue were always too small t o permit of a meltingpoint determination b u t t h e appearance of t h e precipitate was such as t o leave little doubt t h a t i t was actually mucic acid. Considering t h e nature a n d difficulties of t h e method, t h e agreement of results m a y be considered satisfactory. Redwood gave 0.40 and 0.47 per cent; yellow
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T H E J O U R N A L O F I N D U S T R I A L A N D E N G I N E E RI N G C H E M I S T R Y
pine gave 0.96, 0.66, 0.43, and 0.80per cent; sugar pine gave 0.55 and 0.35 per cent of galactan. It is believed t h a t t h e described procedure gave approximately correct results. A critical study of t h e whole galactan method is still much needed, however. DISCUSSION O F R E S U L T S
It is believed t h a t analyses of coniferous woods made b y t h e methods described account for all important constituents of those woods. T h e s u m is in every case slightly over I O O per cent b u t not more so t h a n might be expected from t h e character of t h e methods employed. A variation of several tenths of a per cent between duplicate determinations is usual. The cellulose and lignin are probably always slightly overestimated on account of t h e practical impossibility of getting complete contact between all particles of t h e material and t h e attacking reagents. This difficulty could be partly overcome b y better mechanical condition of t h e wood. T h e possibility of overlapping of values due t o certain constituents being included in more t h a n one determination has received careful consideration throughout these investigations. It is believed t h a t such double estimations have been largely avoided. Most of t h e proximate groups can be shown t o be free from any of t h e constituents contained i n t h e other groups. I t has already been pointed out t h a t this is t r u e i n t h e case of cellulose and lignin. Mannan and galactan determinations depend upon reactions too specific t o admit of t h e inclusion of other constituents. By improving t h e mechanical condition of t h e sample i n respect t o fineness, better results should be obtained i n all t h e determinations. Some of t h e determinations, particularly t h a t of galactan, could probably be made more accurate and reliable. These changes would no doubt give a considerably better summation and a consequently more satisfactory accounting of t h e constituents of t h e coniferous woods. S U 14MA R Y
An improved procedure is described for t h e summative analysis of coniferous woods. Methods are given for t h e estimation of t h e following constituents: loss on drying, benzene extract, alcohol extract, cellulose, lignin, soluble pentosans, mannan, and galactan. 2---By t h e omission of preliminary hydrolysis, more reliable results are obtained in t h e cellulose and lignin determinations t h a n b y methods previously used. 3---Soluble pentosans are determined in t h e chlorination liquors, mannan and galactan on separate portions of t h e original material. Improvements in t h e galactan determination are described. 4--Complete analyses of redwood, yellow pine, and sugar pine are carried out b y these methods. A summation of slightly over I O O per cent is obtained in every case. 5--The results indicate t h a t overlapping of t h e proximate groups, i. e . , partial inclusion of a n y constituent i n more t h a n one group, has been largely avoided. 6--Analyses by t h e proposed scheme probably I-
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account for all important constituents of coniferous woods. REFERENCES I-THIS JOURNAL, 11 (1919). 556. 2-Ibid., 12 (1920), 264. 3--2. Nahr. Genussm , 28 (1914), 177. 9 (1917), 748. 4-THIS JOURNAL, 5-Schorger and Smith, Ibid., 8 (1916), 494. 6-Dore, preceding paper, p. 472. 7-Sieber and Walter, Chem. Abs , E (1914), 1202; Johnsen and Hovey, Paper, [23] 21 (1918), 36; J. Soc. Chem. I n d . , 87 (1918), 1328. 8-THIS JOURNAL, 9 (1917), 748. 9-Cross and Bevan, “Cellulose,” p. 187. 10-Klason, Cross and Bevan, “Researches on Cellulose,” 3, 105; Schorger, THISJOURNAL, 9 (1917), 562. ll-Ibid., 9 (1917), 749. 12-Ibid., 8 (1916), 499. 13-Lindsey and Tollens, Ann., 267, 341; Klason, LOC.cit.; FIaggIund, Biochem. 2 ,70 (1915), 416. 14-Chem. A b s . , 6 (1912), 2958; 8 (1914), 2007. 15-THIS JOURNAL, 7 (1915), 721. 16-Ibid., 8 (1916), 498 (footnote). 17-U. S Department of Agriculture, Bulletin 107, 55.
THE DETECTION OF ARSENIC IN SULFUR By Harold S. Davis and Mary D. Davis MELLONINSTITUTE
RESEARCH, UNIVERSITY O F PITTSBURGH. PITTSBURGH, PA. Received October 23, 1919
OF INDUSTRIAL
A certain sample of sulfur was reported t o contain arsenic. It had been tested by a method first devised b y Schaeppil and later accepted b y many authorities.2 We found t h a t t h e sulfur contained no trace of arsenic, b u t t h a t when i t was tested b y Schaeppi’s method, a decided qualitative test for arsenic was obtained. On further investigation it was found t h a t this method contains a fundamental error which makes it useless as a test for small quantities of arsenic. T h e method as described b y Schaeppi consists essentially in first digesting t h e sulfur with dilute nitric acid for t h e purpose of removing calcium chloride, sulfate, and sulfide. T h e sulfur washed free from acid is now treated with dilute ammonia solution for 1 5 min. a t 7 o o t o 80’ C. Schaeppi assumes t h a t a n y arsenic present in t h e sulfur must exist as sulfide, mainly arsenious sulfide, and will be dissolved b y t h e ammonia. T h e arsenic is then estimated indirectly through determination of t h e amount of sulfide by precipitation with silver nitrate in neutral solution. “For very rough estimations, i t is sufficient t o t r e a t I O g. of finely ground sulfur with nitric acid, t o extract with ammonia, and t o add silver nitrate. From t h e intensity of t h e color or the quantity of t h e precipitate of silver sulfide, i t may be judged whether t h e sulfur is approximately free from arsenic or is strongly contaminated.”3 Schaeppi endeavored t o test t h e accuracy of his method b y dissolving known amounts of pure arsenious sulfide in ammonia solution, carefully neutralizing with nitric acid, and titrating with decinormal silver nitrate using chromate as indicator. His results showed fairly good agreement between t h e quantities of arsenic taken and those found. However, his results would have Chem. I n d . , 4 (1881). 409. Crooks, “Select Methods of Chemical Analysis,” 4th ed., 416; Lunge, “Technical Methods of Chemical Analysis,’’ 1 (1908), 267; Lunge, “The Technical Chemist’s Handbook,” 1916, 107. a Crooks, Loc cit. 1
*
