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DESCRIPTION O F CANADIAN I N L A N D R E V E N U E
TABLS I1 Volume of Benzene Found First Second Runnings Runnings cc. cc.
Total Benzene Found Per cent 0.2 0.2
11 12 13 14
20 20 20 20
.. .. .. 10
0.7 0.7 1.4 1.5
...
... ...
0.1
0.4 0.4 0.7 0.7 1.4 1.6
THE PROXIMATE ANALYSIS OF WOOD By W. H. DORE Received October 21, 1918
0.2
The above table shows only three divergences between the benzene found and t h a t known t o be present. I n every case this is due t o our having neglected t h e precaution we recommend of collecting a second portion of distillate. Such errors are small and only occur where the percentage of benzene is relatively high. Certain experiments which we have made, the details of which need not be given, show t h a t t h e presence of a large amount of acetone in the distillate would increase the apparent ,amount of benzene.
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ANACYTICAL LABORATORY DEPARTMENT OF CUSTOMS AND INLANDREVENUE OTTAWA, CANADA
Benzene Actually Present Per cent
0.2 0.4 0.4 0.8 0.8 1.6 1.6
11,
Pyridine would give a similar result, but its interference can be quite overcome by increasing t o 3 cc. t h e amount of hydrochloric acid added in the oxidation stage of the determination. I t may be noted t h a t determinations can be made more rapidly by the new method t h a n b y the old, t h e accuracy being a t the same time increased, while t h e use of a n arbitrary correction is avoided.
METHOD
T o I O O cc. of the solution t o be tested, 2 0 0 cc. of water are added. No matter how strong the alcohol this is enough water t o bring the sp. gr. above 0 . 9 6 , a n d a moderate excess of water is no disadvantage. T h e mixture is distilled and the first 2 0 cc. of t h e distillate is collected in a suitable graduated vessel. We have found a straight 50 cc. Eggertz tube, divided into tenths of a cubic centimeter, very suitable. It must be provided with a close-fitting straightsided rubber stopper for insertion when t h e distillation is completed. A 50 cc. burette may be substituted for the Eggertz tube if allowance is made for t h e volume of t h e undergraduated portion immediately above the stopcock. Some such straightsided vessel has great advantages over one in the form of a flask, and graduated cylinders with small enough subdivisions cannot easily be obtained. Should i t be suspected, from the appearance of the mixture after dilution, t h a t the benzene present exceeds 0 . 7 5 per cent, it is a wise precaution t o collect a further I O cc. of distillate (making 30 cc. in all) in a separate vessel. This second running should be treated like the first 2 0 cc. and any benzene found i n it should be added when the percentage is being calculated. The rate of distillation should be about I cc. per min., and should not be allowed t o exceed 1.5 cc. per min. To the distillate thus obtained is added 1 5 cc. of potassium dichromate solution ( l / e saturated) followed by 2 cc. of hydrochloric acid (sp. gr. 1.2). After mixing well, the closely stoppered tube is allowed t o stand till an olive-green color develops. Fifteen minutes generally suffices. By careful measurement from a pipette, I O cc. of petroleum ether are next added t o the contents of the tube. The mixture is thoroughly agitated, then allowed t o separate into two layers, and the volume of the upper layer read. This volume less I O cc. gives the percentage of benzene present in the sample. I n the table below will be found the results obtained by this method on the same mixtures employed for our determinations by t h e Holde-Winterfeld- Wolff method. Volume of Distillate Collected First Second EXPT. Runnings Runnings No. Cc. cc.
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This paper is a preliminary report on a study of the chemistry of certain California woods from t h e standpoint of their chemical utilization. As the first step in this investigation a complete proximate analysis of these woods has been undertaken and a consideration of the analytical methods employed and results obtained is herewith presented. There have been numerous contributions t o the literature of wood chemistry in recent years. Most of these have been of a rather scattering nature, but several investigators have undertaken the systematic investigation of the chemistry of particular woods. While much information as t o constituents of wood and methods of procedure has resulted from these studies, the d a t a now available has the defect of not being summative. Examples of complete analyses of woods are practically absent from t h e literature, if we except a few attempts in which the undetermined matter is broadly classified as “non-cellulose material b y difference.” An analysis of a wood in which all of its material is accounted for appears t o have advantages over one t h a t gives a number of constants of the wood without expressing their summative value, from both theoretical and practical standpoints. Our knowledge of the chemistry of wood cannot approach completeness as long as there is a large gap of undetermined constituents. Neither can a wood be completely evaluated commercially until all constituents of possible economic importance have been determined. I n view of t h e exceedingly complex nature of wood a n d the meagerness of our knowledge of wood chemis: try, a complete analysis can mean nothing more t h a n a separation of t h e wood substance into groups of compounds. It appears t o be quite practicable, however, t o effect a grouping of wood constituents on t h e basis of chemical similarity t h a t will have definite theoretical and commercial significance and serve as a starting point for further study. The structural substance common t o all woods is ligno-cellulose, a material in which two constituents (cellulose and lignin) are found and which are believed by most investigators t o be chemically combined. Somewhat allied t o cellulose are the hemi-celluloses, distinguished from true cellulose by a feebler resistance t o t h e action of chemical reagents. These substances are found t o a greater or less degree in all
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
woods. Of a more incidental occurrence are the extractives, a heterogeneous class of bodies found in woocls and believed t o be in the nature of excretory products of the life processes. As their name implies, these extractives may be removed from the woods by treating with solvents without affecting the wood tissue. The extractives include volatile oils, resins, tannins, dyes, and other substances of less common occurrence. The analyses given in this paper.include determinations of loss on drying, exkactives soluble in benzene, extractives soluble in alcohol, substances soluble in water, substances soluble in I per cent sodium hydroxide solution, cellulose, and lignin. It is believed t h a t this classification of wood constituents includes practically all substances occurring in woods and t h a t i t is sufficiently logical and useful t o warrant its adoption. The methods of analysis which are now t o be described have been adapted from a variety of sources. The author has drawn extensively upon the published writings of Cross and Bevan, Konig and Rump, Schorger, and others, for methods of procedure. A recent article by Johnsen and Hovey describes several novel methods t h a t are worthy of attention. Unfortunately the article did not come t o the author's attention until after his experimental work had been performed and he was therefore unable t o make use of the suggestions offered. EXPERIMENTAL
The work here described is a preliminary study chiefly for the purpose of determining the applicability of the analytical methods t o different woods. The figures given are not t o be regarded as necessarily indicating the average composition of trees of the species named, as no special attempt was made t o make the samples strictly representative. Sample I -Redwood (Sequoia sempervirens), a slab 'from a tree about -P ft. in diameter. Composed mostly of sapwood but including a small amount of the outer portion of the heartwood. Not weathered. Sample 2-Yellow pine (Pinusponderosa), and Sample 3, sugar pine (Pinus Eambertiana), were also slabs. Representative of sapwood only. Not weathered. Sample 5-Live oak (Quercus aquifolia), obtained from a number of large chips. Well weathered. Sample 6-Blue gum (Eucalyptus glodulus), a log about 6 in. in diameter. Well weathered. For the analytical sample, fine sawdust was prepared by making a number of cross-sectional cuts with a hand-saw having I I teeth t o the inch. The sawdust so obtained contained a few large fragments of wood which were removed by passing through a 2 mm. sieve. The samples were kept in Mason fruit jars with the 'ids screwed down tight t o avoid changes in moisture content. ANALYTICAL M E T H O D S
g. of the wood are air-dried a t C . in a constant-temperature electric oven t o constant weight. The first weighing is generally made after 16 hrs. drying (over night) and the second LOSS O N DRYING--2
100'
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after 24 hrs, I n most cases there is practically no difference between these weighings. B E N Z E N E EXTRACT-^ g. of the wood, dried for 16 hrs. a t I O O O C., are placed in an alundum thimble and extracted for 6 hrs. in a Soxhlet apparatus. The solvent is evaporated and the residual extract dried for I hr. a t 100' C. A L C O H O L EXTRACT-The extracted wood from the above treatment is extracted for 6 hrs. with 95 per cent alcohol which has been treated with potassium hydroxide t o remove aldehydes and re-distilled. W A T E R SoLuBLE-The above sample of wood, after extraction with benzene and alcohol, is dried a t 70' C. over a steam radiator and transferred t o a 300 cc. Erlenmeyer flask. I O O cc. of water are added and a reflux condenser fitted t o the flask. I t is then boiled on a hot plate for 3 hrs., filtered, washed with hot water, dried for 16 hrs. a t 100' C., and weighed. For these last operations a Gooch crucible having a cotton cloth disk fitted in the bottom is used. The crucible is dried and weighed in a glass-stoppered weighing bottle, both before and after the filtration. The difference between the weights gives the residue after water extraction. The water-soluble material is calculated by adding loss on drying, benzene and alcohol extracts, and residue after water extraction, and subtracting this sum from the total weight taken or from 100 per cent. S O L U B L E I N I P E R C E N T SODIUM H Y D R O X I D E SOLU-
TION-The dried residue after water extraction is transferred t o a 2 5 0 cc. beaker by spatula and camel's hair brush. IOO cc. of I per cent sodium hydroxide solution are added and the beaker is placed in a boiling water bath containing water a t the same level as in the beaker. I t is kept in this bath I hr., then filtered off on the same Gooch crucible and washed well with hot water. Finally i t is washed once with dilute acetic acid (20 per cent), then thoroughly with hot water and again dried in the weighing bottle for 16 hrs. a t 100' C. The loss in weight of crucible and contents since the previous weighing represents material soluble in I per cent sodium hydroxide solution. CELLULOSE--P g. of material dried, extracted with benzene, alcohol, water, and I per cent sodium hydroxide as above described, are washed once with water and the excess water drawn off by suction, The moistened residue is then transferred t o a 300 cc. Erlenmeyer flask in the following manner: The crucible is inverted over a watch glass and the residue forced out upon i t by blowing through the bottom of the crucible. The moist material retains the form of the crucible with the cloth disk upon the top. This is removed with a spatula, the few adhering wood particles are washed off into a beaker, and the cloth is returned t o its place in the crucible. The cake of extracted wood is then placed in the flask by inverting the latter over i t as i t stands on the watch glass and inverting the whole. If a flask with a sufficiently large neck is used this is readily accomplished. Any particles of wood remaining on the watch glass are now rinsed into the crucible as are also those contained in the beaker. They may be transferred t o the flask
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b y a spatula if present in quantity, but a few small particles may ordinarily be neglected as the same filter will be used for the cellulose, and the material will not be lost but will merely escape the first chlorination. These details of manipulation while seemingly complex are quickly and easily carried out after a little practice. The flask containing the moist sample of extracted wood is then fitted with a perforated rubber stopper carrying a glass tube reaching nearly t o the bottom of the flask and terminating on the outside in a short rubber tube. The flask is shaken t o break up the cake and distribute the particles over the bottom and thus offer a greater surface t o the action of the gas. The tube is connected t o the suction pump and the flask exhausted as completely as possible. It is then closed by tightening a pinch clamp upon the rubber tube. The tube is disconnected from the suction apparatus and connected t o a chlorine reservoir. Chlorine gas is slowly admitted, the passage of the gas being judged by the rate of passage of bubbles through a wash bottle containing water, interpos.ed between reservoir and flask. During this treatment the flask is cooled by immersion in a beaker of water. As the sample becomes saturated with chlorine the flow of bubbles becomes very slow. This point is taken as the indication of complete chlorination and the flow is interrupted. The flask is then disconnected and a dilute solution of sulfurous acid is immediately added. The residue is rinsed onto the same Gooch filter and washed with hot water. I t is then rinsed into a beaker and I O O cc. of 2 per cent sodium sulfite are added. The whole is boiled for half a n hour, after which it is again filtered off on the Gooch and washed thoroughly with hot water. To secure the complete removal of lignin i t is necessary t o repeat the entire treatment several times. From 3 t o j chlorinations alternating with the sodium sulfite treatment are required. The completeness of the process is judged by the appearance of the residue which should consist of fibrous material and should be practically free from unchanged wood fragments. The intensity of color imparted t o the sulfite solution is also an index of the quantity of lignin remaining in the fibers. After the process has been repeated a sufficient number of times t o give a pure cellulose, the crucible containing the residue is placed in the glass-stoppered weighing bottle, dried a t 100' C. for 16 hrs., and weighed. I n case the sample contains large fragments of wood they will persistently resist chlorination. Sawdust as ordinarily prepared invariably contains a few such particles and in consequence a n absolutely pure cellulose is not obtained. I n these analyses the residues, after weighing, have always been tested for purity by allowing them t o digest in 7 2 per cent sulfuric acid for 3 hrs. The cellulose is dissolved by this treatment, leaving as a residue any lignin t h a t has not been removed. If appreciable residues are obtained, the mixture is diluted, filtered off on a tared Gooch, washed, dried at IOO', and weighed. The cellulose
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determinations are then corrected by deducting the weight of lignin found. LIGNIPi-2 g. of material are dried, extracted with benzene, alcohol, water and I per cent sodium hydroxide in the same manner as for the cellulose determination. The dried residue is then transferred t o a large Erlenmeyer flask and 20 cc. of 7 2 per cent sulfuric acid are added. The flask is rotated and shaken until all of the wood particles are moistened with the acid, then left t o stand 3 hrs. with occasional attention t o see t h a t all particles come in contact with acid. At the end of t h a t time the cellulose is dissolved in the acid, leaving t h e lignin as a black residue. The mixture is diluted with 50 cc. of cold water and shaken t o ensure moistening of all particles, then 300 cc. of boiling water are added. The residue is filtered off on a tared Gooch similar t o t h a t used in the other determinations, washed thoroughly with hot water, dried in a weighing bottle for 16 hrs. a t 100' C., and weighed as lignin. By the methods described above, the following results were obtained for the five woods examined. The figures given are in each case the average of a. number of determinations. The agreement of duplicate determinations will be discussed later in the article. TABLEI-ANALYSES O F WOODS-AIR-DRYBASIS Results i n Percentages Sample No.. . . . . . . . . . . . . . . . . . . . 1 2 3 5 6 Red- Yellow Sugar Live Blue wood Pine Pine Oak Gum Loss on drying at looo C . . . . . . . . . . . 8 3 3 9.84 8.98 7 . 7 2 10.12 Benzene extract.. . . . . . . . . . . . . . . . . . 0 . 2 9 2.02 0.30 0.06 2.56 Alcohol extract.. . . . . . . . . . . . . . . . . . . 4 . 1 4 1.71 1.36 4.00 2.24 1.54 3.52 1.81 1.98 Water soluble.. . . . . . . . . . . . . . . . . . . . 0.80 7 . 1 5 12.25 9.13 Soluhle in 1 per cent sodium hydroxide 7 . 8 4 10.47 Cellulose.. ....................... 47.58 48.38 48.67 47.52 51.48 Lignin. . . . . . . . . . . . . . . . . . . . . . . . . 27.62 23.60 2 3 . 2 3 1 3 . 5 9 13.28 T ~ T A..................... L
TABLE11-ANALYSES
--
---
96.80
97.12
96.35
83.80 91.24
WOODS-OVEN-DRYBASIS Results in Percentages Sample N o . , . . . . . . . . . . . . . . . . . . . 1 2 3 5 6 Red- Yellow Sugar Live Blue wood Pine Pine Oak Gum 2.22 2.84 0.33 0.07 Benzene extract . . . . . . . . . . . . . . . . . . . 0 . 3 2 4.53 1.49 1.90 4.33 2.49 Alcohol extract .................... Water soluble ..................... 0.87 1.70 2.20 3.81 2.01 Solublein 1 percentsodiumhydroxide 8 . 5 7 1 1 . 5 0 10.13 7 . 7 5 13.63 5 2 . 0 2 5 3 . 1 5 53.98 5 1 . 5 0 5 7 . 2 8 Cellulose ......................... 3 0 . 2 0 2 5 . 9 4 25.77 14.73 14.78 Lienin . . . . . . . . . . . . . . . . . . . . . . . . . . . OF
I
TOTAL. . . . . . . . . . . . . . . . . 9 6 . 5 1 9 6 . 0 0 96.82
82.45
90.26
D I S C U S S I O N O F METHODS A N D R E S U L T S
sAMPLmG-Preparing sawdust is the ideal method of accurate sampling, for the reason t h a t i t is the simplest way of obtaining fine material t h a t represents a complete cross section of any given piece of wood. A cross-sectional disk is equally representative, but t o reduce i t completely t o a state of subdivision suitable for analysis b y rasping, filing, planing, or other means is a tedious and difficult task. If only a part of t h e disk is used, much care is required t o make the portion taken representative of the disk as a whole. Other forms t h a t have been recommended b y various authors for use in the cellulose determination are shavings by Cross and Bevan'" and Schorger,2 and raspings by Dean and Tower,3 Sieber and Walter,* and Johnsen and H ~ v e y . Sawdust ~ has generally been looked upon with disfavor, the objections being t h a t the material tends t o compact and resist penetration of reagents, particularly chlorine gas, and is
* Numbers refer t o corresponding numbers in "References," p. 563.
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difficult t o transfer quantitatively from vessel t o vessel without t h e use of much water from a wash bottle stream.3 I n t h e practice here described these difficulties have been largely avoided and have not appeared t o be more serious with sawdust than in t h e case of similar experiments upon shavings. The first sample used in this work was prepared from a disk l/z in. thick, cut from a redwood slab (Sample I). The analytical sample was made by planing shavings from this disk, cutting along the radial lines. The shavings were then broken up b y crushing. This material proved unsatisfactory both from the standpoint of ease of manipulation and receptiveness t o the action of reagents. Below is given a comparison of the behavior toward chlorine of redwood, in three different mechanical conditions. The coarse sawdust was prepared by a 'circular large-toothed saw. The particles over z mm. in diameter were sifted out. The other samples were prepared as described. TABLS; 111-EFFECT OF MECHANICAL CONDiTION
ON
EASEOF
CHLORINATION
SAMPLE I-REDWOOD Number of Chlorinations
Shavings..
........................
4
4 4 4 Coarse Sawdust.. . . . . . . . . . . . . . . . . . 4 4 4
4
Fine Sawdust..
...................3
Percentage of Lignin in Residue 0.83 0.77 1.61 5.78 0.16 1.64
0.30 1.20 0.53
3
0.14
3
0.54
3
0.48
I t will be seen t h a t more lignin is removed from the fine sawdust in three chlorinations than from the coarse sawdust in four chlorinations, also t h a t it is more uniformly removed. The difference between coarse sawdust and the shavings is not so marked b u t the advantage appears t o be slightly with the coarse sawdust. When i t is remembered t h a t no effort was spared t o secure fine shavings, i t is seen that. sawdust is decidedly t h e more satisfactory form of material. The percentages of cellulose after correction for the lignin in t h e residues agreed equally well in the different forms of materials. Schorgere has found i t practically impossible t o sect;re a residue of cellulose free from lignins in working with shavings. Johnsen and H ~ v e yon , ~the other hand, working with raspings t h a t have passed an 80 mesh sieve b u t not a 100 mesh one found n o , difficulty i n getting a cellulose t h a t is lignin-free. The author's experience has been t h a t the possibility of completely removing t h e lignin by chlorination depends solely upon the mechanical state of the sample. No doubt t h e success of Johnsen and Hovey and the failure of Schorger in t h a t endeavor was due t o the fact t h a t t h e former worked with fine material and the latter with coarse. Fine raspings would, no doubt on account of their uniformity, give a very pure cellulose and, if t h a t were the only consideration, would be the best form of material. The author has preferred t o use fine sawdust, with its inevitable occasional coarse particles, for the reason t h a t the material unquestionably is a properly representative sample of the
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section cut in making it. When the cellulose residue is corrected for the lignin contained in it the result is as accurate as though a pure cellulose had been obtained and objections t o sawdust on the ground t h a t i t does not yield a lignin-free cellulose need no consi der at ion. The selection of material of uniform fineness by the use of fine screens is open t o t h e objection of possibly rendering the sample non-representative, The heavily lignified tissue marking the annual ring, or the grain of the wood, resists mechanical disintegration more than the less lignified material between these rings, and one would therefore expect in the coarser fractions a larger proportion of lignin. The removal of large fragments by a coarse screen does not affect the validity of t h e sample in the same way, as these fragments have practically the same composition as the entire wood. LOSS O N DRYING-The matter of drying wood and cellulose has been investigated by various authors and has been studied quite thoroughly in recent years by Renker.' Cellulose retains water persistently a t temperatures above 100' C. Although the hygroscopic moisture may be estimated with approximate accuracy by drying t o constant weight a t I o j ' to 1 0 7 O , there is no sharp line of demarcation between hygroscopic moisture and water of hydration lost a t higher temperatures. It is apparent therefore t h a t the method here practiced is not t o be regarded as an accurate moisture determination but an arbitrary treatment for certain purposes t h a t require an explanation a t this point. I t is necessary to dry the material a t several stages in the course of analysis and it is essential t h a t the drying should be made each time under the same conditions in order t h a t the results be strictly comparable. It is necessary t o remove most of the moisture before beginning the extraction with benzene in order t o minimize the danger of hydrolysis during extraction. The loss of weight of the wood substance under the same drying conditions as its fractions are later t o be dried is one of the necessary analytical determinations t o be included in a summative analysis. As low a temperature as is compatible with approximate drying should be used t o avoid decomposition of carbohydrates. Taking all of these requirements into consideration, 100' C. appears t o be a logical selection. For convenience a constant-temperature electric oven was used and t h e drying period was invariably over night, or 16 hrs. I n the beginning experiments were made using a vacuum oven and drying at 60' t o 70' C. under 2 3 . 5 in. of vacuum for 11 hrs. The data for weight lost, benzene, extract and cellulose determinations were obtained in the case of redwood so dried, and were found t o be substantially the same as in the case of material dried a t I O O O C. for 16 hrs. Accordingly it was concluded t h a t there was no advantage in attempting t o lower the drying temperature by vacuo methods and the more convenient temperature of 100' C. was adopted and used throughout the work. It was also found t h a t there was practically no
'
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difference in the results of the cellulose determination whether the material was dried after water extraction and extraction with I per cent sodium hydroxide solution, or whether i t was chlorinated without intermediate drying. From this it appears t h a t drying a t IOO O C. probably does not produce chemical changes in cellulose, a t least in the case of redwood. The loss on drying a t 100' C. does not include all of the hygroscopic moisture, but is likely t o include some essential oil. It is a purely arbitrary determination made for summative purposes. B E N Z E N E EXTRACT-A comparison of the amounts of material extracted by various immiscible solvents indicated t h a t benzene extracted slightly more material than ether, petroleum ether, or carbon tetrachloride, and slightly less than chloroform, acetone, or carbon bisulfide. The differences were not marked and the selection of benzene was made in order t o make the results comparable t o those of other investigators who had used this solvent. The chief substances of economic value extracted by benzene are resins and essential oils. A L C O H O L EXTRACT-This fraction contains tannins and coloring matter if these substances are present in the wood. After the extraction of the wood with benzene and alcohol the woodstructure remains practically unaltered. It then consists essentially of lignocellulose or cellulose and lignin in chemical combination with each other. The terms cellulose and lignin as here used do not refer t o two definite compounds, but each represents a class of substances t h a t are more properly referred t o as celluloses and lignins. Normal cellulose or alphacellulose obtained by the purification of the cotton plant appears t o be a single substance with quite definite constants and properties. I n addition t o this alpha-cellulose, oxycelluloses and celluloses having methoxy and furfural-yielding groups have been identified in woods. Besides these true celluloses a great many other carbohydrates are known t o exist in woods. The list includes the hemicelluloses (mannans, galactans, and pentosans) and simple carbohydrates. Probably a great many other unidentified compounds are also present as synthetic or degradation products related t o cellulose and other carbohydrates. For the evaluation of wood for its cellulose-producing power it is necessary t o determine the amount of highly resistant or true cellulose. The ideal method will accordingly include a preparatory treatment which will hydrolyze and remove practically all of the less resistant carbohydrates. I n practice i t is difficult to decide just how drastic a treatment should be employed for this purpose as the line of demarcation between these groups is not well defined. Konig and Rumps have made an extensive study of the substances found in plants. They have divided the celluloses and lignins remaining after the removal of constituents soluble in benzene, alcohol, and water into three groups based upon their resistance t o reagents. These are designated as the proto, hemi, and ortho groups of cellulose and lignin. Protocelluloses and protolignins comprise t h a t portion of the
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tissue t h a t is hydrolyzed and dissolved by treatment with enzymes or digestion with water unaer pressure. The hemicelluloses and hemilignins are removed b y the treatment of t h e residue with I t o 3 per cent sulfuric or hydrochloric acids leaving finally unaffected orthocellulose and ortholignin. With our present limited knowledge of the nature of these substances the chief interest in this classification is the possibility t h a t i t ?ffers of separating the true or resistant cellulose from the less stable carbohydrates. The orthocellulose of the above authors evidently approximates somewhat t o true cellulose, while the distinction between 'proto and hemi forms has probably no particular significance a t this point. The use of a method of acid hydrolysis for separating the hemi groups is open t o the objection t h a t some of the true cellulose might be attacked. Cellulose is quantitatively converted into dextrose by acid hydrolysis under favorable conditions and i t would seem t h a t a partial conversion under the conditions given by the authors might occur. Recently Johnsen and Hoveyg have suggested t h e use of a mixture of acetic acid and glycerin for hydrolyzing and removing the hemicelluloses. These authors claim t h a t true cellulose is unattacked by these reagents. It would seem t h a t this method might furnish a satisfactory distinction between the true and the hemi forms of cellulose. Cross and Bevanlo have used digestion for 3 0 min. with a boiling I per cent sodium hydroxide solution for removing the hemicelluloses. Renker' considers t h a t the treatment with sodium hydroxide solution attacks t o some extent material t h a t should be regarded as true cellulose and t h a t the digestion should be omitted. Schorger" makes the same claim a n d suggests a broader definition of cellulose t o include such hemicelluloses as may survive chlorination and sulfite treatment.12 I n these experiments t h e author has followed the procedures of Cross and Bevan, using the alkaline treatment for the separation of t h e hemicelluloses. The method is arbitrary but has the advantage of paralleling such industrial practices as involve alkaline digestion. A comparison is hete given of two analyses of coarse redwood sawdust (Sample IA). I n one of these t h e alkaline digestion was carried out as described. I n the other, cellulose and lignin were determined upon portions in which the alkaline digestion was omitted. TABLE IV-EFFECTS
O F ALKALINEDIQESTION-REDWOOD Results in Percentages Alkaline Treatment Alkaline Treatment Used Omitted 13.17 13.17 Loss on drying. 0 . 3 2 0.32 Benzene extract.. 3.85 3.85 Alcohol extract.. 0.64 0.64 Water soluble.. 7.38 ..... Soluble in 1 per cent sodium hydroxide.. 45.10 49.11 Cellulose.. Lignin (brown ammonia lignin). 28.45 31.38
........................ ...................... ....................... ........................ .. ............................ ......... T O T A L . . . . ............... ... 98.91
-
98.47
It will be seen t h a t in the case in which the alkali was used t h e amount of cellulose was 4 . 0 1 per cent less and t h e lignin 2.93 per cent less. The sum of these, or 6.94 per cent, represents the hemi forms of these substances dissolved by the sodium hydroxide
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and accounts for most of the 7 . 3 8 per cent sodium the fibers t o a n excess of the gas. This is accomplished hydroxide-soluble material. by first opening up t h e pores of the fiber and the space The water-soluble portion probably contains very between fibers by evacuating the container, then aleasily hydrolyzable carbohydrates and lignin. K l a ~ o n ' ~lowing the chlorine t o be drawn into the vacuum. As has shown t h a t in the case of pine wood, wood gum the substitution in the fiber progresses more gas will and bodies closely related t o lignin are extracted by be drawn in until t h e reaction is complete, when the boiling water. flow will almost stop. This affords a reliable indicaOf the numerous methods t h a t have been devised tion of the completeness of the main reaction, and the for the determination of cellulose the chlorination danger of over-chlorination due t o large excess of method of Cross and Bevan is the only one in which chlorine in the surrounding atmosphere is obviated. the separation is based upon specific reactions of the I n order t o test the extent t o which oxidation is conlignin group. The other methods depend upon selec- trolled by this treatment, a sample of coarse redwood tive oxidation or hydrolysis and have the defect of sawdust (Sample IA) was chlorinated in the ordinary being unable t o remove completely the non-cellulose way in a flask cooled by immersiOn in a beaker of water portion without t o some extent affecting the cellu- a t room temperature. Parallel determinations were lose. made on the same sample in which the flasks were Cross and Bevan'4 long ago demonstrated t h a t when packed in a mixture of ice and salt. Cross and Bevan's moist lignocellulose is brought into contact with chlorine found t h a t by cooling the material t o o o C. during gas the lignin forms a substitution product t h a t is chlorination the yield of cellulose was increased several soluble in sodium sulfite solution. The authors realized per cent, due t o the control of oxidation. If oxidat h a t excessive chlorination resulted in secondary re- tion were not prevented by the method here emactions in which the cellulose was partially oxidized, ployed i t would be expected t h a t the results when the but they showed t h a t by limiting the time of action freezing mixture was used would be appreciably of the gas and cooling the material t o o o C. during higher. An examination of the figures below will chlorination the oxidation reaction could be controlled show t h a t there is practically no difference in the reand accurate results obtained.I5 sults secured by the two treatments, indicating t h a t The method of Cross and Bevan has been critically oxidation is probably completely controlled without studied by Renker' who, in addition t o limiting the the use of special cooling. TABLE V-EFFECT OF COOLING-COARSE REDWOOD SAWDUST time of chlorination and cooling, adds sulfurous acid Results in Percentages solution immediately after chlorination t o prevent Total Lignin in Residue Residue Cellulose oxidation. More recently Schorger has made use of Coarse sawdust, water-cooled, 4 chlorinations 45.08 0.16 44.92 the same agencies. 46.63 1.64 44.99 45.42 0.30 45.12 The chlorination as accomplished by Cross and 46.74 1.20 45.54 sawdust, in crushed ice and salt, 4 Bevan and by Schorger has been carried out by spread- Coarse chlorinations.. . . . . . . . . . . . . . ... . . . . . . .. . 44.95 0.08 44.87 45.70 0.54 45.16 ing the material out in beakers and causing a slow flow of chlorine into the beakers so as t o bathe the fibers The d a t a given in the above tabulation show the continuously in fresh gas. The work of all these usual agreement of duplicate cellulose determinations. authors tends t o show t h a t after sufficient chlorine A variation of several tenths of one per cent is t o be has been absorbed t o form the substitution com- expected ordinarily. It should be stated t h a t deterpound any further exposure t o the gas results in partial minations in which there is a high lignin correction are oxidation of the cellulose. The only effective control generally unreliable and such determinations have therefore is t o limit the time of chlorination. The been excluded from the averages. As examples the first chlorinations were of 3 0 t o 60 min. duration, the following figures for yellow pine and blue gum are later, 1 5 t o 30 min. quoted. Sieber and and more recently Johnsen TAELEVI-AGREEMENT OF CELLULOSE DETERMINATIONS Results in Percentages and Hovey,g carried the reaction on in Gooch cruciTotal Lignin in bles BO arranged t h a t the chlorine gas is drawn through Residue Residue Cellulose Sample 2, Yellow Pine.. , . , . . . . . , . 4 8 . 4 0 0.11 48.29 by suction. Using fine rasped material, these authors 49.29 0.52 48.77 52.22 find 4 chlorinations of 2 0 , 15, 15, and I O min. with 2.29 49.932 48.19 None 48.19 the usual intermediate sulfite treatments sufficient 48.27 None 48.27 51 . s o 1.37 50.13% t o remove all lignin without any oxidation effects. 48.36 None 48.36 2.09 53.80x This method has manipulative advantages in t h a t the Sample 6 , Blue G u m . . . . . ., ...... . . 55.89 51.54 0.26 51.28 material remains in the same vessel throughout the 51.84 0.31 51.53 53.15 1.53 51.62% procoss. I n all of the methods here described the material is The figures marked x are those having large lignin kept in an atmosphere containing an excess of chlorine corrections and in all cases but one the results are over t h a t required for the substitutive reaction and considerably higher than those with small lignin cori t is attempted t o stop the reaction a t about the time rections. The differences between duplicate lignin this reaction is completed and before oxidation begins. determinations were of about the same magnitude as The method used by the author in this investigation in t h e case of cellulose. differs from these in t h a t oxidation is controlled by The method used for the determination of lignin is limiting the amount of chlorine used and never exposing t h a t used by KOnig.'B This author found t h a t by
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treating extracted wood with 7 2 per cent sulfuric acid after the method employed by Ost and Wilkening,l7 there remained a residue of non-cellulose material or lignin. Later Konig and RumpS found t h a t in this treatment proto- and hemilignins were dissolved by the sulfuric acid as were also a part of t h e ortholignins. The black residue remaining was termed by these authors “colored ortholignin.” It is evident t h a t this “colored ortholignin” is not a measure of the full lignin content of the wood. Apparently it bears some definite relation t o true lignin and von FellenberglS has advanced the theory t h a t Konig’s ortholignin differs from true lignin by 2 molecules of water. For true lignin the formula C22H19(CI-18)209is proposed and for Konig’s colored ortholignin CZ2H15(CH3)207. If these relations hold, the weight of residue obtained by the method here used may be calculated t o true lignin by multiplying by a factor t h a t corrects for t h e two lacking molecules of water. As derived from t h e ratio of molecular weights of t h e above compounds this factor is 1.086. As a test of the applicability of this correction t o t h e results obtained the figures for lignin in t h e case of t h e three coniferous woods examined have been multiplied by 1.086 and t h e sum of t h e constituents using t h e new figures has been determined. TABLE VII-CORRECTION
OIL LIGNINDETERMINATIONS Results i n Percentages 1 2 5 Red- Yellow Sugar wood Pine Pine 27.62 23.60 23.23 Konig’s colored ortholignin.. . . . . . . . . . . . . . . . . . . . . . Above figures X 1.086 (von Fellenberg’s true lignin) 3 0 00 2 5 . 6 3 2 5 . 2 3 Sum on basis of Konig’s lignin.. . . . . . . . . . . . . . . . . . .9 6 . 80 9 6 . 3 5 9 7 . 1 2 Sum on basis of von Fellenberg’s lignin. . . . . . . . . . . . 9 9 . 1 8 9 8 . 3 8 9 9 . 1 2
It is seen t h a t the totals using this correction are considerably closer t o I O O per cent t h a n those using the figures obtained by analysis in the case of t h e coniferous woods. These findings are consistent with von Fellenberg’s theory and indicate the possibility of an accurate lignin determination based upon the method of Konig with a factor correction. A more complete study of the relation between these two forms of lignin will be required, however, before these figures can be accepted. The author intends t o make a further study of these relations. The totals shown in Tables I and I1 indicate t h a t in the case of t h e coniferous woods practically all of t h e constituents are accounted for, while.with the hardwoods such is not t h e case. This is a t least partly due t o t h e nature of the lignin. The lignin obtained from the coniferous woods appears t o be a homogeneous substance having the same physical form as t h e original material. I n t h e case of t h e two hardwoods examined, there appeared t o be a certain amount of material of an appearance somewhat similar t o t h a t of the coniferous woods; but in addition a large amount of colloidal substance was obtainable. It is evident t h a t the lignin of the hard woods is a much more complex substance than t h a t of the conifers and t h a t the method of Konig for its determination does n o t apply in the case of ,the former woods. Johnsen a n d HoveyIg have come t o a similar conclusion, as they state t h a t the method of treating with 7 2 per cent sulfuric acid applies t o spruce and other
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conifers but fails entirely with the broad-leaved trees. I n carrying out t h e lignin determinations considerable hot water was required t o wash out t h e sulfuric acid. The dried residue had a black appearance and i t was thought t h a t this might be due t o charring during the drying. Several determinations were carried out in which t h e material was washed slightly with 4 per cent ammonium hydroxide solution followed by hot water t o ensure t h e removal of all sulfuric acid. By this procedure a dull brownish residue was obtained t h a t was somewhat heavier than the black lignin. Two samples of this brown material were Kjeldahled and yielded 0.32 per cent and 0.3 I per cent of nitrogen, while a sample of t h e black material yielded only 0 . 0 5 per cent. This indicated t h a t t h e brown material had taken up ammonia either by absorption or the formation of a compound. Lignin is generally believed t o possess acid properties and t h e formation of an ammonium salt with lignin i s not unlikely. The black substance, even after drying, gradually changed over into t h e brown substance on prolonged digestion in 4 per cent ammonia solution showing t h a t the black color is not due t o charring, but is the natural color of the substance. The possibility of the presence of cutin in woods requires a brief consideration a t this point. Cutin is a constituent of barks and epidermal plant: tissues generally. I t appears t o be occasionally present i n the wood substance of trees. Konig and Rump20 have reported t h e presence in fir and beech of 0 . 1 4 per cent and 0 . 1 3 per cent cutin, respectively. Cutin is a white substance of waxy appearance and characterized by high resistance t o chemical reagents. I n the methods here used it remains with the cellulose after chlorination and with the lignin after treatment with 7 2 per cent sulfuric acid. If present in t h e woods i t would have been left with the lignin correction residue found after treating the cellulose with 7 2 per cent sulfuric acid. I n the case of only one wood, t h e oak, was any material found t h a t might have been this substance. I n t h a t wood a small amount of substance corresponding t o t h e described properties of cutin was obtained but in insufficient quantity to definitely identify i t as such. Apparently cutin is not a constituent of importance in the tissue of woods. I n recent years considerable attention has been devoted t o t h e determination of certain constants of woods. These constants include the furfural-yielding groups, methoxy, formyl, acetyl, and acetic residue groups. SchorgerZ1 and Johnsen and HoveyZ2 have lately contributed determinations of these groupings in certain American woods. These determinations are generally considered as constants of the woods but are in reality constants of constituents of the woods. It appears t o t h e author t h a t a study of t h e distribution of these constants in the groups, separated according t o the scheme outlined in this paper, will have a considerable interpretative value. It is his intention t o make such a study. I n general, i t may be said t h a t the methods used in this investigation when applied t o the conifers account
June, 1919
T H E J O V R N A L OF I N D U S T R I A L A N D E N G I N E E Ri X G C H E M I S T R Y
for practically all of t h e material of t h e woods. I n the case of t h e hardwoods, the method for lignin is not applicable, due t o the entirely different and highly complex nature of t h e non-cellulose constituents. SUMMARY
I--Methods for t h e summative analysis of woods are described and analyses of five California woods by these methods given. 2--Sawdust is found t o be t h e most satisfactory mechanical condition of wood for analytical purposes. 3--Cellulose in wood is determined by a modification of the Cross and Bevan method involving chlorination. in vacuo. The cellulose residues are tested for the presence of lignin and corrections applied when necessary. 4-Lignin is determined by Konig’s method with 7 2 per cent sulfuric acid. The probable relation of lignin so obtained t o true lignin is discussed. ;-In t h e analysis of coniferous woods by these methods 96 t o 9 7 per cent of t h e wood constituents are accounted for. I n t h e case of t h e hardwoods examined, the lignin determinations fail and only 83 t o 9 1 per cent of t h e wood constituents are obtained. 6-Cutin is not a constituent of importance in wood tissue. REFISRENCES 1-Cross and Bevan, “Cellulose,” 2nd ed., p. 244. 2-Schorger, THIS JOURNAL, 9 (1917), 557. 3-Dean and Tower, J . A m . Chem. Soc., 29 (1907). 1125. 4-Sieber and Walter, Chem. A b s . , 8 (1914), 1202. 5-Johnsen and Hovey, Paper, 21 (1918), 40. 9 (1917), 564. 6-Schorger, THISJOURNAL, 7-Renker, J . Sac. Chem. I n d . , 28, 1269. 8-Konig and Rump, Z . N a h r . Genussm., 28 (1914), 177-222. 9-Johnsen and Hovey, P a p e r , 21 (1918), 42. 10-Cross and Bevan, “Cellulose,” 2nd ed., p. 95. 9 (1917), 564. 11-Schorger, THISJOURNAL, 12-Schorger, I b i d . , 9 (1917), 562-3. 13-Klason, Cross and Bevan’s “Researches on Cellulose,” 3, p. 105. 14-Cross and Bevan, “Cellulose,” 2nd ed., p. 102. 15-Cross and Bevan, I b i d . , p . 96. 16-Konig, Chem.-Ztg., 36, 1101. 17-Ost and Wilkening, I b i d . , 34, 461. 18-von Fellenberg, Chem. A b s . , 11 (1917), 2122. 19-Johnsen and Hovey, Paper, 21 (1918), 50. 20-Konig and Rump, Z . Nahv. Genussm., 28 (1914), 186. JOURNAL, 9 (1917), 560. 21-Schorger, THIS 22-Johnsen and Hovey, P a p e v , 21 (1918), 48. DIVISIONOF AGRICULTURAL CHEMISTRY UNIVERSITY O F CALIFORNIA AGRICULTURAL EXPERIMEXT STATION BERKELEY, CALIFORNIA
T H E DETERMINATION O F IODIDE IN MINERAL WATERS AND BRINES’ By W P. BAUGIIMANAND
w. w.
SKINXER
IKTRODUCTIOX
A large number of methods have been proposed for the determination of iodine in t h e presence of bromide and chloride and this in itself would seem t o indicate t h a t t h e problem has not been satisfactorily solved. A colorimetric method, depending on t h e liberation of iodine by nitrous acid and determining 1 Read before the Division of Water, Sewage, and Sanitation, 56th Meeting of the American Chemical Society, Cleveland, September 10 t o 13, 1918.
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the amount by the intensity of t h e color imparted t o a few cubic centimeters of carbon bisulfide, developed by Struve,l modified by Haywood,2 has been adopted as a tentative method for the determination of iodide in mineral waters by t h e Association of Official Agricultural chemist^.^ This method has been studied by the Association of Official Agricultural Chemists and the results reported by one of US.^ This report shows t h a t t h e method gives fairly satisfactory results when applied t o mineral waters and brines containing only one or two milligrams of iodine per liter, b u t t h a t it is not satisfactory when larger quantities are t o be determined. The palladious iodide and thallous iodide methods are reported t o give satisfactory results, b u t t h e reagents required, palladious nitrate and thallous sulfate, are expensive and not always available. The indirect methods are not suitable where one halogen greatly predominates. Most of the other proposed methods are based on t h e behavior of solutions of t h e haloids towards oxidizing agents. Very few, if any, oxidizing agents have been overlooked in the search for a solution of the problem, but some have been only superficially investigated and their limitations not established. An endeavor has been made in this investigation t o determine t h e limitations and suitability of a few of t h e methods which seemed most promising and t o modify them as necessary so t h a t results obtained by their use might be accurate and reliable. CHEMICALS USED
CHLORIDE-The chemically pure reagent was dissolved in water and reprecipitated with hydrochloric acid gas, removed from the liquor b y filtration, and finally heated in a porcelain dish until all of the hydrochloric acid had been driven off. It was further purified by several recrystallizations from distilled water. SODIUM BROMIDE-This was a stock reagent and was purified by recrystallization several times from distilled water. S T A N D A R D POTASSIUM IODIDE SOLUTIOX-Potassium iodide was synthesized according t o the method employed by Gooch and B r o ~ n i n g . ~Pure iodine was prepared by twice resubliming C. P. iodine from a small quantity of potassium iodide. Three-fourths of the iodine was added t o a n excess of electrolytic iron and covered with distilled water. When t h e iodine had disappeared, t h e solution was decanted from the excess of iron, the remainder of the iodine added, t h e solution filtered into a large volume of boiling water t o which a quantity of potassium bicarbonate, exactly equivalent t o t h e iodine, had been added and t h e precipitated iron oxide removed by filtration. It was then made up t o a convenient volume and standardized by precipitating and weighing t h e iodine as silver iodide from aliquot parts by volume. SODICM
Z . anal. Ckem., 8 (1869), 230. Bureau of Chemistry, Bulletin 91. s “LMethods of Analysis,” 1916, p. 47. 4 “Report on Water,” W. W. Skinner, Referee A . 0. A . C., Bureau of Chemistry, Bullelin 162. 5 A m . J . Scz., 39 (1890), 196. 1
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