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Slightly lower results are given by t h e Devarda method as herein modified t h a n b y t h e nitron method. 5-The method has been successfully used on thousands of soil samples representing varied conditions as t o t y p e a n d treatment. It has also been applied with satisfactory results t o crop samples. THE PROXIMATE ANALYSIS OF HARDWOODS: STUDIES ON QUERCUS AGRIFOLIA By W. H. Dore UNIVERSITY
OF
CALIFORNIA AGRICULTURAL EXPERIMENT STATION, BERKELEY, CALIFORNIA Received May 26, 1920
I n previous papers’ t h e author reported methods for t h e summative analysis of wood, and analyses of three coniferous woods and two hardwoods. It was shown t h a t t h e procedure succeeded with t h e coniferous woods b u t not with t h e hardwoods. The present investigation was undertaken for t h e p u r p w e of modifying t h e original scheme so as t o make it applicable t o t h e latter. Studies made upon one of the hardwoods (Quercus agrijolia), with which t h e original methods were unsuccessful, have resulted in a satisfactory accounting for t h e constituents of t h a t wood. Further work is necessary t o establish i t as a method applicable t o hardwoods in general. T h e failure of t h e original scheme with t h e hardwoods was partly due t o t h e fact t h a t Konig’s 7 2 per cent sulfuric acid method for lignin does not give reliable results with t h e woods of t h e broad-leaved trees. This has been observed by Johnsen a n d Hovey2 as well as b y t h e present author3 and more recently by Konig and B e ~ k e r . ~These last authors have made a comparative study of KBnig’s sulfuric acid method, t h e 4 2 per cent hydrochloric acid method of Willstatter,6 and a method of treatment with gaseous hydrochloric acid, as applied t o woods. They found t h e three methods equally applicable t o t h e coniferous woods, b u t with t h e hardwoods the hydrochloric acid methods alone gave t h e full yield of lignin. T h e gaseous hydrochloric acid method was recommended b y these authors for t h e broad-leaved woods. It appeared probable t h a t t h e methods used previously for t h e analysis of t h e coniferous woods might be advantageously applied t o t h e hardwoods, with t h e substitution of t h e newer method for lignin. Experiments were accordingly conducted with the object of working these o u t with the hardwood mentioned. I n addition t o t h e changes made in t h e lignin determination, attention has been given t o t h e possibility of t h e presence of constituents not found in t h e coniferous woods. PREPARATION O F MATERIAL
T h e material used in this investigation was the wood of coast live oak (Quercus agrifolia) in t h e form of fine sawdust. A sound branch about 5 in. in diameter was obtained, t h e bark removed, a n d cross-sectional cuts THISJOURNAL, 11 (1919), 556; 12 (1920), 264, 476. 21, No. 23 (1918), 36; also J . SOC.Chem. I n d . , 37 (1918), 132t. THIS JOURNAL, 11 (1919), 562. ‘2. angew. Chem., 32 (1919). 155; through J. SOC.Chem. I n d . , 88 1
a Paper, 8
(1919). 5300. 6
Ber., 46 (1913), 2401; through Chem. Abs., 7 (1913), 3412.
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made by a fine saw ( 1 3 teeth t o t h e inch) until t h e quantity of sawdust amounted t o about 1 5 0 g. The sawdust was sifted through a sieve having 50 meshes t o t h e linear inch. The oversize was dried a t I O O O C. for several hours, after which i t was ground t o pass through t h e 50 mesh sieve. T h e entire material was then well mixed and preserved in a screw-top Mason fruit jar t o avoid changes in moisture content. I t was t h e intention a t t h e beginning of this work t o use t h e same analytical methods as were employed previously for t h e coniferous woods, with t h e single exception of t h e method for lignin. It was soon discovered, however, t h a t simple extraction with benzene and alcohol did not produce a complete purification of t h e wood tissue from adventitious substances, as shown by the formation of a brown solution on washing with cold water, preliminary t o chlorination. The use of t h e former procedure was objectionable in t h a t i t afforded no means of estimating the water-soluble constituents, which would accordingly not be accounted for in t h e summation. Furthermore i t was found, as will be shown later, t h a t this wood, when extracted with benzene and alcohol only, gives unsatisfactory results, as t o yield and quality of product, in both t h e cellulose and lignin determinations. The method finally adopted t o overcome these objections was t h a t of following t h e bepzene and alcohol extractions with successive digestions in cold water a n d cold dilute sodium hydroxide solution. T h a t redwood cellulose is unaffected by this treatment has been pointed out by t h e auth0r.l Oak cellulose is similarly resistant. ANALYTICAL METHODS
Methods for determining loss on drying, benzene extract, a n d alcohol extract are identical with those previously described in t h e case of coniferous woods.2 SOLUBLE I N COLD WATER-The residue from t h e alcohol extraction was dried, transferred t o a 2 5 0 cc. beaker, 2 0 0 cc. of cold water added, and t h e mixture allowed t o digest for 2 4 hrs. It was then filtered off on a tared Gooch crucible provided with a filtering disk of mercerized cotton cloth, washed, dried for 16 hrs. a t I 00 O C., a n d weighed in a glass-stoppered weighing bottle. The difference between weights gives t h e residue after water extraction. T h e amount soluble in cold water is calculated by adding together t h e percentage figures for loss on drying, benzene a n d alcohol extracts, a n d residue after water‘ extraction, a n d subtracting this sum from IOO per cent. SOLUBLE I N COLD
5
P E R CENT SODIUM HYDROXIDE
soLurroN-The residue from t h e water-soluble determination was transferred t o a suitable beaker, a n d roo cc. of 5 per cent sodium hydroxide solution were added. T h e mixture was left for 2 4 hrs., then filtered off upon t h e same Gooch crucible as before. It was washed thoroughly with water, several times with dilute acetic acid, and finally with water. After drying for 16 hrs. a t 100’ C. i t was again weighed. T h e loss in weight from t h e previous weighing represents 1
2
THISJOURNAL, 12 (1920). 268. I b i d . , 12 (1920), 477.
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
material soluble in cold j per cent sodium hydroxide solution. c ~ ~ ~ . u ~ o s ~ - C e l l u l owas s e determined upon t h e residue from t h e above successive treatments. The analysis was carried out b y t h e Sieber and Walter method previously described b y t h e author.' LIGhm-For this determination t h e gaseous hydrochloric acid method of Krinig and Becker was employed, with slight modification. The method proposed by these authors consists in adding 6 cc. of water t o I g. of t h e wood (previously extracted with benzene and alcohol) in a test tube, then passing" gaseous hydrochloric acid through t h e mixture until it is thinly liquid, in t h e meantime cooling t h e t u b e by immersion in ice. I n t h e present investigation t h e wood was moistened with ordinary concentrated hydrochloric acid instead of with water. Excessive evolution of heat was thereby avoided, and cooling by simple immersion in water was found sufficient. Fou;- samples were run a t t h e same time. Amounts of I g. each were subjected t o t h e same purification treatment as for t h e cellulose determination, transferred t o I X I O in. test tubes, and treated with about I O cc. of concentrated hydrochloric acid. The test tubes were closed with rubber stoppers, each containing two glass tubes for t h e introduction and exit of t h e gas. The inlet tubes extended nearly t o t h e bottom of t h e test tubes. Hydrochloric gas, generated by dropping concentrated hydrochloric acid into strong sulfuric acid, was passed through t h e tubes containing t h e mixtures of wood and hydrochloric acid for about z hrs. The tubes were left closed for 24 hrs., then diluted, and t h e contents filtered on tared Gooch crucibles containing mercerized cotton cloth filtering disks, washed thoroughly, dried for 16 hrs. a t 100' C., a n d weighed in glass-stoppered weighing bottles. P E N T O S A K S K O T O T H E R W I S E A C C O U S T E D FOR-The filtrates and washings obtained in four cellulose de' terminations were combined and evaporated to a little less IOoo cc', transferred to a one-1iter flask, and diluted t o t h e mark. Aliquot portions of I 2 j cc. ( = I g. of mood) were placed in 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 i n the usual manner. The furfural was Drecinitated a s phloroglucide, and t h e precipitate filtered off, washed, dried, and weighed. T h e results were calculated t o pentosan b y means of Krober's tables.2 The furfural-yielding constituents of oak are partly soluble in t h e alkali solution and most of t h e insoluble portion remains with t h e cellulose. The small amount unaccounted for with either of these proximate groups is found in t h e chlorination filtrates and washings. MASYAS (RESIDUAL)-Ten grams of wood were dried, extracted with benzene a n d alcohol, and digested in water and j per cent sodium hydroxide solution as before. then hydrolyzed with hydrochloric acid (sp. gr. 1.02j ) , and t h e mannan determined by precipitation a s mannose phenylhydrazone. The details of t h e method have been described in a previous paper.
An attempt was made t o determine total mannan by direct hydrolysis of t h e raw wood, b u t , owing t o t h e interfering action of tannin or other substances dissolved from t h e wood, i t was unsuccessful. G A L A C T A N (RESIDUAL)-FiVe grams of wood were prepared as before, b y successive extraction. The purified material was evaporated with nitric acid and t h e galactan converted into mucic acid b y t h e method described for coniferous woods.' FURFURAL AND METHOXY DISTRIBUTION-The methods used were those described in a previous paperel RESULTS O F EXPERIMENTS
The composition of oak wood as found b y these methods is given in Table I. The figures are in every case averages of two or more determinations. TABLEI-COMPOSITION OF LIVE OAK WOOD(Ouercus aguifolia) CONSTITUBKT Loss on drying.. . . . . . . . . . . . . . . . . . . . . . . . . . . Benzene extract.. . . . . . . . . . . . . . . . . . . . . . . . . . Alcohol extract.. . . . . . . . . . . . . . . . . . . . . . . . . . . Soluble in cold water, . . . . . . . . . . . . . . . . . . . . . Soluble in cold 5 per cent sodium hydroxide. . Cellulose. . . . . . . . . . . . . .. .. Lignin. . . . . . . . . . . . . . . ........... Pentosans not otherwise accounted f o r . . . . . . Mannan (residual). . . . . . . . . . . . . . . . . . . . . . . . . Galactan (residual). . . . . . ......
TOTAL ...............................
1
THE JOURNAL 12 (1920), 267. Bruwne, "Handbook of Sugar Analysis," Appendix, p. 83
Air-dry Basis Per cent 4.20 0.50 4.33 3.66 1 8 . 71 45.48
Oven-dry Basis Per cent 0:52 4.52 3.82 19.53 47.47 21.14 1.97 Nil 1.56 100.53
20.25
1.89 Nil
-
1.49 100.51
I n this table t h e first five groups of substances represent extraneous matter removed from t h e wood in t h e course of t h e purification process, while t h e last five groups represent substances contained in t h e residual purified tissue. The amounts obtained for each of t h e first five groups vary considerably with t h e manner in which t h e determinations are carried out, b u t t h e weight of purified residue remaining is in all cases about t h e same. I n Table I1 t h e individual, as well as average values are given for constituents of t h e purified tissue, also for t h e yield of purified tissue.
Y
f
985
,
TABLE11-COMPOSITIONO F PVRIFIED WOODTISSUE (Results in percentages of air-dry material, 4.20 per cent moisture) -IndividualAverage Cellulose ...................... 45.33 45.04 46.19 45.38 45.85 -;; ";ti;;;i;;' 20.03 20.47 20.25
32;;;; ~
~
~
~
~
~
~
: :d: : ~: : :~
TOTAL ....................
~
::: ~
Residue after extraction (purified tissue) ...................... 68.80
i
1.89 ~
68.50
~
~
i
~
.
, 1 . .4 9 , ~ : : ___
69.11
68.86
68.22
68.60
The separate extracts obtained i n t h e purification process have not been systematically examined. The benzene extract, consisting probably of oils and resins, is trifling in amount, as would be expected from t h e non-resinous character of t h e wood. T h e alcohol extract is a reddish brown material, consisting of tannin and possibly other coloring substances. T h e water and alkali solutions contain coloring substances not completely removable by alcohol extraction. I n addition, t h e alkali solution contains a considerable amount of furfural-yielding groups. Two portions of t h e solution, on distillation with I 2 per cent hydrochloric acid, yielded furfural corresponding t o I 1.47 and 1 1 . 1 1 per cent of pentosan. Two determinations of t h e acetic acid yielded by t h e raw wood upon hydrolysis with 2 . j per cent sulfuric acid gave 4.j1 and 4.84
* THISJOURNAL,
12 (1920). 472.
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per cent, after correction for formic acid by t h e method given in a previous paper.’ The residue after digestion in sodium hydroxide solution yielded only traces of volatile acids. The series of treatments therefore removes t h e readily hydrolyzable acetic-yielding groups. I t appears probable t h a t t h e cleavage of acetic groups takes place during t h e alkaline digestion, rather t h a n during t h e less drastic extractions t h a t precede i t . The alkaline extract could not be directly examined for acetic acid, because acetic acid had been introduced during the washing of t h e wood residue. The alkali-soluble portion probably consists chiefly of pentosans, substances yielding acetic acid upon hydrolysis, and tannin or other coloring substances. To determine whether oak cellulose is injured by t h e treatments with cold water and alkali, cellulose determinations were made upon material so treated, and also upon material extracted with benzene and alcohol only. The products were examined by t h e mercerization test of Cross and Bevan.2 The results of these experiments are given in Table 111. I
T A B L E 111-INFLUENCE
O F W A T E R AND ALKALI DIGESTION ON Y I E L D AND QUALITYOF C E L L U L O S E
(Results in percentages of air-dry No. of Chlorina- Total tions CelluPRELIMINARY TREATMENT Required lose Extraction with benzene a n d alcohol only . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 46.18 8 44.79 9 45.69 8 44.23 AVERAGE.. . . . . . . . 45.22 Extraction with benzene a n d alcohol a n d digestion in cold water a n d alkali .......................... 4 45.33 4 4.5.04 4 46.19 4 45.38 AVERAGE. 45,48
........
wood) a-
8-
-P
Cellulose
Cellulose
Cellulose
29.38 27.94
10.08 12.60
5.33 5.15
32.93 32.99 33.75 33.80
14.34
I t will be seen t h a t t h e average of cellulose is practically t h e same in both cases, b u t t h e partly purified material requires much longer chlorination t h a n t h a t which was thoroughly extracted, in order t o obtain a product equally free of lignin. The agreement of individual determinations is much better with t h e completely extracted material. The fully extracted material yields more a - and more /3-cellulose t h a n t h e partly extracted material, showing t h a t , in t h e latter case, t h e excessive chlorination effects a partial degradation of t h e a-cellulose t o lower forms. It was found difficult t o obtain t h e @-cellulosein a form t h a t could be filtered and washed. The single determination in t h e case of completely purified material is obviously inexact, as t h e s u m of a- and P-cellulose is greater t h a n t h e total cellulose. The results for a-cellulose, however, afford a reliable comparison of t h e quality of cellulose by t h e two processes, and show t h a t a much better product is obtained when t h e alkali treatment is used. The effect of t h e water and alkali treatment upon t h e lignin was also studied. Material completely extracted gave 20.03 and 20.47, per cent lignin. Material extracted with benzene and alcohol only gave on three determinations 22.11, 2 3 . 7 2 , and 2 5 . j 3 per cent of lignin. The latter results are variable and considerably higher t h a n those on t h e completely ex-
* THISJOURNAL, *
12 (1920), 474. “Paper Making,” 1916 Ed., p. 97; THISJOURNAL, 12 (19201, 267.
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tracted wood, due probably t o t h e partial retention of substances soluble in sodium hydrqxide solution b u t not in hydrochloric acid. Preliminary treatment with t h e alkaline solution is therefore essential t o obtaining a pure lignin. The methoxy content of lignin is not changed b y t h e alkaline digestion, as will be shown later in this article (see Table V). A study of t h e distribution of t h e furfural-yielding groups in t h e wood gave t h e results shown in Table IV. TABLE IV-DISTRIBUTION
OF FURFURAL-YIELDING GROUPSIK 0 . t ~ (Results in percentages of air-dry wood, 4.20 per cent moisture) -Ai Furfural-As PentosanIndividual Av. Individual Av. U n t r e a t e d wood.. . . . . . . . . . . . . . . . 13.12 1 2 . 6 9 1 2 . 9 0 22.38 21.65 22.01 Completely extracted w o o d . . , , , , , 6 . 8 4 6 . 8 2 6 . 8 3 11.7 1 11.68 11.69 Solubleincold5percentNaOH.. 6 . 7 1 6 . 5 0 6 . 6 0 11.47 11.11 1 1 . 2 9 . . . . . . . . . Nil . . . . . . Nil Soluble in cold water TOTAL (compare with untreated wood). . . . . . . . . . . . . . . . . . . . . . . . . . . . 13.43 . . . . . . 22.98 I n cellulose.. . . . . . . . . . . . . . . . . . . . 6 . 1 2 6 . 10 6 . 1 1 10.70 1 0 . 6 7 1 0 . 6 8 In chlorination solutions. . , . . , . , , 1 . 1 5 1 . 0 5 1 . 1 0 1 . 9 8 1 , 8 0 1 . 8 9 I n lignin.. . . . . . . . . . . . . . . . . . . . . . . . . . . . Si1 . . . . . . Kil T O T A L (compare with completely extracted wood) . . . . . . . . . . . . . . . . . . . 7 . 2 1 . . . . . . 1 2 . 57
*
__-
_-
-_
__
I t will be observed t h a t slightly more furfural was obtained from t h e fractions into which t h e wood was separated t h a n from t h e wood itself. The same relation also holds with respect t o t h e furfural yield from t h e fractions composing t h e completely extracted wood. The yield is variable, depending upon t h e conditions maintained during t h e analysis. By separating t h e material into several portions and subjecting each t o t h e treatment prescribed for t h e pentosan determination, t h e opportunity for furfural production is extended, and increased yields are t o be expected. With this explanation, t h e d a t a in Table I V may be regarded as. consistent. The distribution of methoxy groups is shown in Table V. TABLE\‘-DISTRIBUTION O F M E T H O X Y GROUPSI N O A K (Results in percentages of air-dry wood, 4.20 per cent moisture) Individual---Av. 5.68 5 , 4 5 5.56 U n t r e a t e d wood. . . . . . . . . . . . . . . . . . . . . Wood extracted with benzene a n d alcohol 5.56.. . . . . . . . . . . . . . . . . . . . . . . . . .5 . 8 7 5 . 2 5 Completely extracted w o o d , . . . . . . . . . . . 4 . 4 3 4 , 3 6 4 . 2 1 (3.71) 4,33 1,ignin in wood extracted with benzene 3.56 a n d alcohol., . . . . . . . . . . . . . . . . . . . . . 3.73 3.40 Lignin in completely extracted w o o d , . .. 3 . 5 3 ( 2 . 9 4 ) 3.53 1 Figures in parenthesis omitted from average.
--
The method and apparatus used gave good results with pure vanillin (20.3 j per cent against 20.4 theoretical). Considerable difficulty was experienced, however, in getting concordant results with wood a n d lignin. This is believed t o be due partly t o imperfect contact between reagent and material, and partly t o losses incidental t o t h e excessive manipulation required in preparing t h e necessarily small sample for t h e determination. While there is considerable variation between duplicate determinations, t h e d a t a nevertheless indicate marked differences in t h e methoxy content of t h e different preparations. DISCUSSION
The methods here applied t o oak wood as a typical hardwood may be regarded as fulfilling t h e following requirements of a satisfactory procedure for a summative analysis: ( I ) They account for practically all of t h e material of t h e wood. The s u m of constituents is as close to
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I O O per cent as could be expected with methods of this stances present in oak wood: t h e pentosans soluble in character. cold, dilute, sodium hydroxide solution, t h e furfural( 2 ) As compared with other procedures tried, yielding constituent of t h e cellulose, and t h e commaximum yields of cellulose and lignin are obtained, paratively small amount of pentosan, resistant t o t h e with a minimum of impurities or degradation products. alkali treatment b u t dissolved during chlorination. It would appear t h a t t h e first of these is wood g u m (3) Overlapping of constituents is avoided. The (xylan or araban), and the second oxycellulose. T h e cellulose was found free from lignin. T h e studies of Konig and Becker have shown t h a t t h e gaseous hydro- last may be due t o more resistant pentosan or t o chloric acid method gives a cellulose-free lignin. T h e pectin. T h e simultaneous presence of galactan and galactan is determined by a method too specific t o methoxy groups not due t o lignin suggests t h e latter. T h e present investigation indicates t h a t alkaline include either of these constituents. T h e other constituents are determined in separate successive extrac- digestion is necessary for t h e best results with oak wood, tions and cannot therefore overlap with t h e above and presumably with t h e hardwoods generally. From t h e work done so far, it would appear t h a t t h e conif“residue constituents.” erous woods should be prepared without, and t h e (4) N o substances of importance have been overlooked. I n addition t o constituents specifically named hardwoods with, alkaline digestion. Further work is in:the analysis, woods are known t o contain in greater necessary t o determine whether this rule is generally or less amount: acetic-yielding groups, furfural- applicable. It appears probable t h a t t h e method of yielding groups (pentosans, etc.), methoxy groups, alkaline digestion will be found effective with all cutin, pectin, nitrogenous substances, and ash. A highly colored woods. S U NMlA R Y brief consideration of t h e available d a t a will show t h a t these substances are largely accounted for in t h e I-Methods previously used for t h e analysis of fractions deter mined. coniferous woods were investigated as t o their appliIt has been shown t h a t t h e groups yielding acetic cability t o t h e hardwoods. Oak wood, as a typical acid on hydrolysis are wholly contained in t h e extracts hardwood, was analyzed by suitable modifications of removed in purifying t h e wood tissue. A study of t h e these methods. with t h e results herein presented. furfural distribution shows t h a t t h e pentosans are fully a-The purification treatment employed for t h e accounted for, partly in t h e alkali-soluble portion a n d tissue of coniferous woods (successive extraction with partly in t h e chlorination filtrates and washings. benzene and alcohol) was supplemented with digestion T h e balance of t h e furfural yield is from t h e cellulose. in cold water and cold j per cent sodium hydroxide The methoxy distribution shows t h a t these groups are solution. These treatments remove all adventitious largely associated with t h e lignin. Most of t h e substances, b u t do not injure either t h e cellulose or t h e methoxy groups t h a t are not so associated are accounted lignin. for in t h e water- and alkali-soluble portions. A small 3-Lignin was determined by t h e gaseous hydroamount (0.8 per cent), however, is apparently split off chloric acid method recently proposed by Konig and during t h e hydrochloric acid treatment, and this portion is unaccounted for in t h e s u m of constituents. Cutin B ecker. 4-The modified procedure conforms t o t h e requireis absent, as shown by t h e complete solubility of t h e cellulose residue in 7 2 per cent sulfuric acid. Precise ments of a satisfactory analytical scheme in t h a t i t accounts for all of t h e material of t h e wood, yields t h e information is lacking as t o t h e chemical nature of maximum amount of main constituents free from impectins and their occurrence in woods. I t is known purities or degradation products, avoids overlapping t h a t pectin contains methoxy, and yields furfural on distillation with hydrochloric acid and mucic acid on of constituents, and overlooks no constituents of imevaporation with nitric acid. T h e presence of galactan, portance. pentosan, and non-lignin methoxy groups in t h e residutl may be taken as a possible indication of pectin. NITRATE CONTENT OF CERTAIN WATERS CONSIDERED If so, i t is largely accounted for in its above-mentioned BACTERIOLOGICALLY SAFE’ decomposition products. By M. Starr Nichols T h e purified wood tissue after successive treatments WISCOXSINS T A T E LABORATORY O F HYGIENE, U N I V E R S I T Y O F &’ISCONSIX, with t h e four solvents contains only a few tenths of MADISON, WISCOXSIN a per cent of nitrogen and a similar amount of ash. The quantity of nitrate nitrogen permissible in a Presumably these small quantities are distributed potable water has been t h e subject’ of much consideraover t h e constituents cellulose and lignin. S o con- tion and speculation. While every sanitarian has his siderable error can result from neglecting t h e m alto- own quantity standard upon which he bases his judggether ment as t o t h e source and quality of a given water, As has already been noted, t h e composition of t h e each agrees t h a t a large amount of nitrate nitrogen various extracts has not been fully worked out. I n cannot be disregarded. Richards and Woodman2 say, their aggregate, t h e amount of these extracts measures “ I n eastern America nitrates above 0 . j part per million t h e total amount of adventitious substances, as dis- wouldarouse suspicion, and above j parts per million tinguished from t h e wood substance proper. 1 Presented at t h e 59th Meeting of t h e American Chemical Society The distribution of furfural-yielding groups shows S t Louis, Mo , April 12 t o 16, 1920. 2 “Treatise on Air, Water, and Food,” 3rd E d , 1811, p 92. t h a t there are probably three forms of these sub-
