1032
I X D U S T R I A L A N D E N G I N E E R I N G C H E Ibf I S T R Y
Vol. 24, No. 9
points of consumption. One possible solution is the shipment of the fused sulfide product to consuming centers where it by a lowmight be converted into potassium temperature roasting process.
ACJSOWLEDGMEST The writers received very valuable assistance from Alton Gabriel, who identified products by petrographic examination and the application of qualitative chemical microscopy.
SUMMARY
LITERATURE CITED
Preliminary experiments have shown that polyhalite is rapidly reduced by hydrogen at temperatures above 800’ C. Loss of potash by volatilization apparently is low a t 950” C. but increases markedly with further increase in temperature. The potash content of the reduction product is removed rapidly and completely by a simple extraction with hot water. Evaporation of the extract yields small quantities of potassium sulfate and potassium sulfite and a relatively large amount of an essentially sulfide material which, on drying, has a content of 51 per cent potassium or 61 per cent potassium oxide, and on fusion a content of 64 per cent potassium or 77 per cent potassium oxide.
(1) Schumann, Ann., 187, 286-321, especially 303, 306 (1877). (2) Storch, ISD.ESG.CHEV.,22, 934 (1930). (3) Storch, Bur. Mines, Rept. Investigations 3023 (Oct., 1930) (4) Storch and Clarke, Ihid., 3002 (June, 1930). (5) Storch and Fraas, Ihid., 3062 (Feb., 1931). (6) Storch and Fragen, Ibid., 3116 (Sept., 1931). (7) Storch and Fragen, IXD.EXG.CHEM.,23, 991-5 (1931). (8) Treadwell and Hall, “Analytical Chemistry,” 5th ed., vol. 11, pp. 350-2, Wiley, 1921. (9) Wollak, 2. anal. Chern., 77, 401-0 (1929). RECEIYEDMarch 1, 1932. Presented before t h e Division of Industrial and Engineering Chemistry a t t h e 83rd Meeting of t h e American Chemical Society, New Orleans, La., March 28 t o April 1, 1932. Published by permission of t h e Director, U. 9. Bureau of Mines. (Xot subject to copyright.)
Physical Structure of Coal, Cellulose Fiber, and Wood as Shown by Spierer Lens REINHARDT THIESSEN, Pittsburgh Experiment Station, U. S. Bureau of Mines, Pittsburgh, Pa.
T
HAT coal is a colloid has been accepted for some time, and many of the phenomena related to its uses have been laid to its colloidal nature, such as theories of plastic flow, agglutination, behavior in coking, etc. Examinations of very small particles by ordinary ultra-microscopic means have shown that coal particles are composed of ultramicroscopic particles or micelles, but have given no idea of their size and arrangement in the coal structure. Recently Spierer (23, Zd), a Swiss physicist, introduced a new type of lens involving the principle that light reflected by colloidal particles is greatest opposite the direction of the illuminating ray. With this new tool the study of the colloidal nature of coal and other organic substances related to coal was resumed with unexpected results. Kot only was the colloidal structure of coal shown but also the arrangement of the micelles and their relationship to that of the original arrangement in the living plant from which they were derived. I n order to present a more comprehensive meaning of the colloidal structure of coal and its relationship to living plant matter, the successive steps in the development of the knowledge of the structure of the cellulose fiber will be reviewed briefly.
STRUCTURE OF CELLULOSE FIBER Although it had been known that cellulose fibers were optically anisotropic, Nageli in 1858 (18) advanced the hypothesis that the structural unit of cellulose fiber consists of a linear anisotropic crystalline micelle; he rounded out and further developed his well-known micelle theory, in which he postulated that all organic substances, such as cellulose fibers, cellulose membranes, starch, and birefractory animal substances, were built up of submicroscopic anisotropic particles which he called micelles, the anisotropic property of the substance being determined by the nature of the micelles themselves. Every individual micelle behaves as a small crystal, and the larger the number of these crystals in a unit area, the more intensive is the resulting interference color of the transmitted light beam. The elasticity axes of the micelles are
oriented with respect to the axis of the fiber. All examined organic substances are alike in that one of the three axes is located radially and the other two tangentially. Many of the phenomena observed could not be explained in any other way than by the micelle theory. Nageli further accounted for the phenomenon of smelling of substances by the micelle theory. Water penetrates only between the individual micelles, never into them. Not much weight was given to this theory. In fact, it was vigorously combated until better apparatus and research methods were developed, when it gained in meaning and importance; it is now proving t o be correct in many particulars. Gilson (7) was the first to actually demonstrate the crystallinity of cellulose in that he treated thin sections of radish and beet successively with weak potassium hydroxide, ether, cupramnionia, and ammonia. After such a treatment, bundles of crystals became visible under the microscope, giving all the microchemical tests of cellulose. Gilson’s results were verified by ,Johnson (15) in 1895. Many years later the crystallinity of cellulose was again attacked by means of the x-ray. After Debye and Scherrer (5) had developed the method of x-ray analysis of pulverized substances, Ambronn ( I ) in 1917 advanced the idea from a theoretical consideration that, if cellulose consists of crystalline particles as is shown by its double refraction, it should give an x-ray spectrum in monochromatic light. Stimulated by this suggestion, Scherrer, although unsuccessful in his first attempt ( E ) , obtained in 1918 (21) definite x-ray spectrograms from ramie fibers. He showed that crystals were oriented in the fibers, and thus verified the theory that the double refraction of the ramie fibers is due to the double refraction of bars and to the individual crystalline particles forming the bars. Herzog and Jancke ( I I ) , in the meantime, carried out investigations in the same direction on cotton fibers, ramie fibers, wood, artificial silk, and viscose, obtaining definite interference diagrams in all. The diagrams obtained from wood were remarkably similar to that of cotton and ramie. From this they reasoned that the lignin was absorbed on the
INDUSTRIAL AKD ENGINEERING CHEMISTRY
September. 1937
surface of cellulose crystals or layered b e t w e e n the crystal particles, but was not ohemically united. Later Herzog, Jancke, and Polanyi (2,10,1R,29) definitely found that the crystallites lay parallel to one another and to the crystallographic axis of the fiber. I n the meantime, Polanyi developed and devised means to d e t e r m i n e the dim e n s i o n s of the crystallites in cellulose and gave for the first time such d i p e n s i o n s : the Q axis = 10.2 A,, b axis 7 7.9 A , , and c axis = 8.45 A. He further calculated that such a unit gave room enough for four glucose molecules. Herzog and his co-worker. (9, 12) extended these measurements to the crystallites of a number of substances. They further determined the unit cell to consist of four glucose groups and to be of a rhombic symmetry. They also determined that the dimensions of the crystallites of cellulose nitrate and cellulose acetate differ but little f r o m t h o s e of the original untreated cellulose, a condition necessary for assuming topochemical reactions:
AXIS a
b c
CELLTLOSE
A. 8.60 7.78 10.22
CELLLT- CELLULOSE
LOSE
KITRATEA C E T ~ T E A. A. 10.1 8.6 10.8
9 2' i . 1
'3.8
gl u c os e molecules and that there are 40 to 60 chains in the micelle. I n this crystallite, the molecular dimensions or the space lattics are 8.6 A. in the a axks, 10.3 A. in the b axis, and 7.8 A. in the c a x i s . T a k i n g t h e m e a n of t h e n u m b e r of glucose molecules in the chains and of the number of chains in the crystallite, the magnitude ,Of a crystallite would be 400 A . or $0 m i l l i m i c r o n s wide, 750 A. or 7 5 omillimicrons long, and 600 A. or 60 millimicrons thick. No conclusion was made concerning their form, but it is shown that they are easily orientated and must be oblong. Seifriz (ZJ), expanding the norks of Sponsler and Dore, and of hIeyer and Mark, emphasizes the structure of the glucose residue and the fact that the glucose residue is constructed as a typical carbon ring of 5 carbonand 1 oxygen atoms. To such a ring there is joined by an oxygen bridge another which is the reflected image of the first. These two units as a pair, linked between carbons 1 and 4, constitute one link in the cellulose chain. By repeating this link some twenty times, the cellulose chain is formed. Seifriz considers this the nearest approach to what can be regarded as a cbellulose molecule. The length of the cellulose chain is regarded as not fixed and is capable of reaching any length. There is, therefore, no cellulose molecule in the strictest sense. The whole field of x-ray investigation on cellulose has relaying particular stress cently been summarized by Clark (4, on how the architectural plan accounts for the actual physical and chemical properties of natural and regenerated fibers employed as textiles. The studies are further carried into the growth of the fiber by Wanda K. Farr and into the structure of wood by G. J. Ritter. We have, therefore, a fairly good picture of the structure of the cellulose fiber with some agreement by all investigators, as worked out by x-ray methods. There is as yet no agreement as to the exact structure of the micelle (17, %)-whether the whole micelle is to be regarded as one large molecule, whether the long chains are to be regarded as long-chain molecules, or whether a group of eight glucose units are to be regarded as free molecules. Also, we cannot obtain as yet a clear idea of the form or of the size of the micelles, except that they must be rodlike and of indefinite length. Theoretically, the micelles postulated by x-ray methods should be visible by ultra-microscopic means. This can be done when cotton fiber and bits of wood are reduced to small fragments and observed under the ordinary ultra-microscope, but this method shows nothing definite as to their arrangement in the fiber, their relationship to each other, or their size,
The physical structures of cellulose fiber, wood, and coal as seen by the Spierer lens are described and shown by photographs. An attempt has been made to correlate the observations thus made with the structure of the same substances as determined by x-ray methods. The author has not tried to interpret in all cases what the Spierer lens reveals, or to reconcile the Spierer pictures not in accord with those constructed after x-ray diffractions. That coal is a colloid has been generally accepted for some time. Investigations by means of new methods by vertical illumination, particularly as used in the Spierer lens, not only give conclusive ei)idence of the colloidal nature of coal but also show the arrangement and the size of the micelles in coal. The micelle arrangement in coal, as f a r as preserved, is similar to that of the plant tissues from which the coal was derived. The micelle structure of plant tissues is clearly shown and no longer leaves a n y doubt that wood 3bers or cellulose fibers, as in cotton and ramie, are definitely built up of micelles in characteristic arrangement, and verify the Nageli micelle theory and !he structure postulated by x-ray methods. I n semirotten wood the individual micelles are similar in arrangement, but stand out more clearly than in sound wood; in wood in a more advanced stage of decay, the micelles stand out still more clearly, yet their original arrangement has been retained. Transifion stages f r o m sound wood to well-rotted wood indicate that there is a close relationship between cellulose and lignin in wood. I n the woody derivatives of brown coal, lignite, and sub-bituminous coal, the original arrangement, although progressicely more or less disarranged, is clearly and unmistakably shown.
The size of particles in colloidal solutions of cellulose nitrate as determined by the diffusion method corresponds exactly to the dimensions of the crystallites computJed from the x-ray diagrams. Sponsler and Dore (25) next developed the long-chain structure theory of cellulose. Irvine and Hirst (14), having shown that cellulose is made up of glucose molecules, assumed that the structure, as recognized by the x-ray spectrum, consists of crystallites composed of glucose molecules. The cellulose crystallite, i t was therefore concluded, is made up of parallel chains of glucose units having an amylene oxide ring and united alternately by a 1-1 and 4-4 linkage, a group of eight glucose units completing the cellulose molecule. The parallel chains, extending lengthwise of $he fiber, are separated from gne another by a distance of 6.10 A. in one direction, and 5.40 A. in the direction at right angles to it,Jhe component part of the chain being repeated every 10.25 A. The next important work was contributed by Meyer and Mark (16). They concluded that the micelles of cellulose consist of parallelly arranged primary valence chains of glucose locked together by means of micelle or secondary forces, in parallel layering, into crystallites or micelles, the bonds in the chains being effected by 1-4 glucosidal oxygen bridges. From diffusion and x-ray spectrum data they concluded that a crystallite, or micelle, consists of 1500 to 2000 glucose molecules, and assumed that a chain consists of 30 to 50
1033
ZM I S T K Y I U 1) I 1 S T II I A L A N U 13 N G I N E E R I h‘ G C I i I
1034
because of the small size of tlie fragments necessary for the examination. By means of blre Hpierer lens (gb) tlie physical structure of cellulose and similar substances may now be studied. Some
Val. 24, No. 9
fiber. A close examuiation (better observed under the microscope than in illustrations) reveds many slight indentations (or knottiness) often regularly spaced along the strife. This phenomenon may be observed in every cotton fiber examined. This constant recurrence sur& has a meanina.
surfaces o f a ribbon. Each in&vidual fiber, as in the cotton fiber, shows a number of strin~. Their average spacing is also tlie same, as far as can be dcterinined~--namely,twelve to results obtained with this Iens iverc published for the first time every 10 microns, or 83,? millimicrons each. in America. by Seifriz (U). The latter shows the micelle The question now arises, do these st.ri:r in tlie cotton and structure through a number of t.lieramie fibers represent the obdrawings of the cellulose walls of long units or micelles, postulated by x-ray methods, lodged end to elder pith and of living onion end and forming the apparently skin, rind through photomicrographs, taken with the Spierrr continuous striz, or, in other lens, of a cell wallof cider pit.11, of words, the fibrils postulated by thesurface of an oriiiin skin, s l i d some investigators? The striz of a transvcrse section of threc rcprcsented are not necessarily adjoining cells of a11 oriiuii shin. coritinuous and may consist of LO The object of ihk wort’L 1s ’ miit5 closely aligned one above e x t e n d these observations iind tlie other. In fact: as already show thestructure of cotton fiber, stated: constrictionsoften seen at ramie fiber, grcen wood, sound re&r intervals or a knottiness dry wood, slightly rotted wood, dong the strksuggest that they arc built up of closely aligned and well-rotted wood, and finally uiiit particles. Assuming that lignite, s u b - b i t u m i n o u s , and very small puticles of an oblong bituminous coals by mealis of this lens. An endeavor is f u r t h e r shape are lodged closely end to made to show the relationship of end, the halo formed by the intense illnniination of the unit parthe colloidal structure of living plants, of which coal has been ticles will overlap and thus make formed, to that of the coal-the the lineup appear more or less end produet of processes of ferc o n t i n u o u s . The striie may m e n t a t i o n , putrefaction, and FIGURE 2. Spremn PHOTOOEUPU OP R ~ ~ ~ , .lialrle ~ : therefore actually represent rows FIBERS( x 1000) coalifactioii of plant substances. of uriits of certain lengths and widths, The d i m e n s i o n s , as The s t u d y is b e g u n with the cotton and ramie fibers because the greatest progress in the far as they can he determined, are of the eame magnitude a6 knowledge of the niicelle structure as well as the chemical detemiined from the x-ray data. The conclusion, therefore, atmrtme. of has been attained in cotton and ramie. -.rdlnlosn .-..-~. This knowledge, it is believed, will convey a better meaningto themicelle sbriieture of wood,rotted wood,and coal. A cotton or ramie fiber is composed essentially of pure cellulose, but wood is composed of cellulose, lignin, and a few other minor substances embraced under the term “hernicellulose.” The two, therefore, differ greatly in chemical composition. The question is, how do they differ in micelle structure? Next a study of partially rotted to well-rotted wood should he of interest and value in that it shows the transition from the original structure to that of a substance changed chemically by bacterial decomposition. A study of well-rotted wood has shown that nearly all or much of the cellulose has disappeared and that the lignin largely remains. I n this connection it should also he of interest to compare witli it wood from which the cetlulose has been removed by chemical reagents. The fur- can be drawn that the stria, as seen ill the fiber, represent the ther transition from well-rotted wood to coal should, there- crystallites or micelles arranged in orderly rows. fore, afford an interesting link. 1knJnE 1. SPleBEn COTTON I’lHER
1bOTOCRAPW
OF
( X 1000)
~~
STRUCTURE OF VISCOSEFIREI~
hllCELLE slTiUCTUIlE 01’ COllTON AND R A M I E ALED BY SPIEIlEIt 1,EX-S
finEIlS
A Spierer pliotograph of a cotton fiber is showrr in Yigure 1.
It will be noticed that a number of strin: mi parallel to the
The Spieror picture of viscose fiber should throw some light on the conclusions that the stria: represent rows of micelles. Viscosc, a colloidal solution of cellulo~e,is forced through minute orifices. 00 exposure to a coagulating solu-
SeDtembw, 1932
1 N D U S T R I A-L
A N D E N G I N E E R I N G C H E M I STR Y
FIOUHE 4. THUW~EBSE SECTION OF WOODOF Pdocarpus TAKEN WITH 2-MM.OII,-IB%MEHSION APOCH~OMATIC OnIECTWE TO SHOW GENEHAL APPEARANCE OF WOODFIm n IN Tzmxsvmm SECTXONS, AS SHOWN BY O H D I N ~ Y METHODS( x inon) Middle larnollae are distinotly shown but three layers uaualiy described annot be made out, instead d I~rgernumber of eoncentric l~yen are indisti?cetly $m&. Number and width 01 lajiere amee with those seen with S~iererlens.
tion, the viscose coagulates, leaving the colloidal particles or micelles of cellulose in tile form of fine threads. A Spierer photograph of a rayoii fiber is shown in Figure 3. It will be noticed that the micelles are actually seen as individual rodlike particles. I n the process of the formation of a fiber they have oriented themselves parallel to the long axis of the fiber, with a tendency towards a chain arrangement, although not carried out completely. As closely as can be determined from the surface, there are hetween ten and thirteen (average, twelve) chains to each 10 microns, as in caw cotton, mercerized cotton, and ramie fibers. The lengths of the individual micelles, as seen in the microscope, vary considerably; it is impossible to determine average lengths. All of the longer and many of the shorter rods iiwe constrictions, indicating that they are formed by the joining of shorter particles. From this evidence it seems safe to conclude that the stria in the cotton and the ramie fibers are the rod-shaped micelles placed end to end and pnroliol to the long axis of the fibers.
STRUCTURE OF SOUND CONIPEROUS WOOD The wood of ordinary conifers, such BS pine, hemlock, spruce, and balsam, consists of long hollou~boxlike fibers, running parallel to the long axis of the stcm, arranged in concentric layers or rings from the center of the stern outwards, and further arranged in tiers radiatiag from the center to the periphery. I n a transverse section the cut ends of the fibers present roughly rectangular outlines (Figures 4 to 6 ) . The wall of a wood fiber is said to con& of t i m e or four layers: the middle lamella, the primary layer, the secondary layer, and the tertiary layer. It is a difficult matter to distinguish between tliese layers since, generally, variations from a few to a number of layers may be seen in the transverse nection. Figure 6 , a transverse section of the stem of a Mic~onjcas,is a good type to illustrate the various layers.
1035
FIGUHE 5. Tn.k,usvEHsE SECTION OF WOOD OF Podmwpus TAKEN WITH SPIEnEn LENS FROM S a M E SECTION AND NEAR SAMZ PLACE AY FIGURE 4 ( x loon) ~ e e n;i Figure 4, taken b y drsnsmittad lieht, ia disiioctly shown.
Covrsntric larsriag laintly
from one another by a very thin layer--the middle lamellurn, rn. It is composed essentially of lignin and stands out sharply from
the other part of the wall, staining blue with a safranin-gentian violet stain. The middle lamellumis bounded on either side by B thin Is. er the primary layer, p . This layer is ala0 relatively thin. ft &ov be distineuished from the other lavers hv it8 lighter color. .Next f o l l o k the relatively thick secoidary bye< s, and then, against the lumen, 1, comes the tertiary Payer, t. Bordered pits are shown 8s bp. I n many fiber8 these layers n a y be distinguished clearly. More often, hoaever, there is a dist.inct repetition, and the specific layers, whether priniary, secondary, or tertiary, cannot be determined, as is shown in the wall between 01 and b.
lIJJ6
a'
Ftoti~e 8.
I ~ U I A LSECTION OP B A L ~ A M FIR TAKENWITH Srrexr:x LENS
While the cliemical nature of cellulose is quite well known, that of lignin is still far from being solved; although the physical structure of the cellulose fiber, such as cotton and ramie, is also well known through x-ray inetliods, the knowledge of that of wood is Ear from being satisfactory. The relationship of the cellulose and lignin in wood, although much discussed, in yet unsolved. L i p i n is generally considered to bo amorplio~is,giving diffraction patterns with only one or two diffuse rings (4). Ness (23) sags that all modern refined methods of investigation show that in the cell wall cellulose is not clierrically bound to its other componeuts. IIeraog and Jancke reason Sroin x-ray data that, the ligniii is not chemically combined with the cellulose crystallites but is absorbed on the surface of the cellulose crystals or layered heinmen the crystal particles. Freudenbcrg and eo-workers ( 6 ) niwintairi thHt ligiiiii shows
FIUVHti
9. TANGENTIAL SECTION
OF
BALSAM FIR
The primaiy, secondary, m d tertiat3- layeia are iomposed essentially of cr:lliJose (approximaii:lg 50 per cent), lignin (approximately 30 per cent), alld Iminicollolase (:approximately 20 per cent) \VItile the diSferent Iqyer.; mag lie distiiigitishod i i i o r ~or lest clearly in f l 4 i m x , c m , in . tionr of other ~ ~ m i i o layering is less definite. (Figure 4) betweeii t h e e and SrencTuitr: OF I'lCNlN Since lignin is universally ociatcd witli cellulose ii, wood (the two being regarded a gnocelluiose), its nature and struct,urc must bc t.aIien into consideration. SXIYJILE A N D
1037
F I G U ~11. E LOXGITUDINAL SECTION OF WOOD PHOM SAMESAMPLE AS FIGURE 10 ( X 1 0 0 )
FIGU~W 12. THANSVERSE SECTION OF CONIFEROUS WOOD IN ADVANCED STAGE OF DECAY ( x 1000)
no indication of double rdraction, either witti the polariniog microscope or with x-ray methods. Lignin, in wood, he says, exists in the form of a fundamental amorphous medium to be compared with a mass of felt in which the cellulose crystallites are embedded. After the removal of the cellulose micelles, as by tlie sulfuric acid method, the crystallites leave oblong vacant spaces in the lignin. These vacant spaces hold tangential positions parallel t.o tfie cross section of the fiber. The vacant spaces are the cause of weak double refraction, which is the sanie as that claiinetl by other investigators to be true double refraction of lignin. Chemically, they say, lignin must he considered as formed in two stages. The fundamental molecule of lignin is that of a coniferyl alcoliol. On the average, twelve such molecules are combined through condensat,ion into polymers. These polyiners are in the form of
Froune 14.
T n n ; a v z ~ s eSECTION OF W s r l c I'IYH Csl.L.or.r,sc Efns Bx:" Ilr:Mo"I.:D
FROM WHlc"
( X 1000)
P'icun~13. LONGITUDINAL SIETIONOF PEATWOODIN ADVANCEDSTAGEOF DEC4Y ( X 1000)
elrains, npproainiately 100 .I. in lengtii. At tlie death of the plant, or whcn attacked by chemical reagents, these chains are further combined by condensation or polymerization into larger aggregates. These aggregates should be visible under the ultra-microscope, The general opiriion semis to he that lignin is amorplious, is not siiown in x-ray spectra, and is not chemically combined wit,lior rrlnted to the cellulose in wood.
Smucsuar; o v COX~WEIUJUS Wouo .AS Jmli ny S i m m n I, of coniferous wood with the Yor the study of tlre atruet Spierer h s , a number of species of conifers were t.al;eii and all gave similar results. Figure 7 reprcseents a transverse section, Figure 8 a radial section, and Figure 9 it tangeridial section of balsam fir, magnified 1000 diameters. The transverse section shows one complete rvood fiber, surrounded by six others shown in part.. Tlie walls of eaclr sliow definite concentric striations, consistinp of alternatr dark arid light lilies parallel to t,he middle Inmclla. T'nder tlie niicrorcope these stria appear as alternate dark and brightly illuniinatrd lines. At a close scrutiiiy, tlie illuminated linc re seen to I~RVC! nodes or knots. h2easiiremrnts slioa tlint they art: quite equally spaced, averaging ten bright lilies to every 10 microns. The lentioular forms (Or)) in the radial walls are from bordered pits. In the radial s d o n (Figure 8) wliicli is cut longitu-
tW8
I N I)U S 'I K I A I. A N D
I?: N (2 I N IC E I1 I N (2 ( 2 I 1 E >I 1 S 1'I< Y
dinally and psrallcl tu Llit: rays (as indicated lig the planes, *-a' and b-b' in Vigore T ) , the two tangential walls, t , are seen edgewise, T l i c s e walls on either side of the films again show up as coneisting of longit,udiiial strii. of alternate dark and brightly illiiniinated lines. A s in the transveme sections, the
bright lines are siiowii to possess nodcs, in some places quite definite and at regular intervals. The radial wall, 7, or that part of the wall bctween the tivo tangential walls, t , and parallel to the section is riot vinible under the Spierer lens. l riglit angles and reThe rays of light penetrating tlie ~ y n l at flected on to it from tlic mirror in the objective are not absorbed or reflected ami there is a void. T h e part of tlie wall in question contain8 a 1ium11cr of iiordr:rd pits, but these are only very slightly perceptiiilc. In t,iie tangential section (Fignre 9), indicated in Figure 7 by tlic plancs c-c' and il-d',
Vol. 24,No. 9
section, the ultcrnrtte dark and bright lines foim leiiticular areas. The character of t.he striation is the same as in the transverse and the radial sections. A careful examination sliows that tbep are not continuous but consist of micelles placed in rows in close succession. The tangential part of the wall between the two radial walls, or that part of the wall at right angles to the axis of the microscope again is not visible, with tlie exception of a few indistinct stri:r and sinall particles on it. The illuminated lines may be conccived of as cut ends and sides of thin sheets, formed by a series of chains of micelles placed closely one ahove tbe other, aiid by a large nutuber of such chains placed side by side. The wood fiber may therefore be considerrd as being built up of a number of con-
F I G U ~ 17. E Loucn'uumaI. SECTION OF WOODY STRUCT~~RE SHOWNIN FIGUtil? 13, UUT PliRPEXDICuLAR TO IIEDblXG 1'LANE
( X 1000)
centric sheets or thin t.ubes one inside tlie other, each tube being formed by long chains of miccllcs placed side by side and completing a lube. In some ~\-oodsthese chains rnn parallel to the long axis; in others they deviate considerably from the long axis and form spirals. OF GRBENDica1,lilletlones WOOD An examination of the wood of a number of dicotyledonous plants revealed essentially the same structure under the Spierer lens as tlie wood of the conifers. I n green or living mood the individual micelles are shown more definitely than in dead or dried woods.
MICELLAR %XIJCTURE
FIGURE16. IANGITUUINAL SECTION OF WOODY STR~JCTURE SHOWN IN FIGUI~E 15 AND PARALLEL TO BED nwG PLANE (x 1000) Mioeliea a ~ g e a rin straight cox8 in edges of fiber wsils. snd in ~ p i i exirangemcnt i in walls between edges of mioeiies.
the radial walls, f-, are seen edgewise. Those parts of the all^ between the bordered pit, bp, are shown as alternate dark and bright parallel lines. I n the bordered pits cut by the
COXPABISON OF CELLULOSE AND WOODFIBERS A comparison of the structure of the cellulose fiber, such as cotton and ramie, with that of wood shows that they are essentially the same, except in the width of the spacing of the stri;e. The distance in the cellulose fiber is approximately 0.833 micron, whereas that of wood is 1 micron. I n the cotton and ramie fibers where there is no lignin, the stri;e are produced by the cellulose micelles alone; in the wood fiber they must be produced either by the cellulase micelles alone or by micelles consisting of both cellulose and lignin. If the lignin is amorphous and consists of ultra-particles, it should be visible under the ultra-microscope. But neither the cellulose nor the lignin (or, in other words, the lignocellulose) is visible in any part of the cell wall when seen in the direction at right angles to ita surface. The way in whicb the two are related, whether chemically combined or merely physically associated,
G I N EEKING
C II li M I S T R
Y
1039
aniined, both in t r longitudinal sections. Figure 12 sho~vsa trans, of a conifer, including part of the sprinF; and part of the autumn wood. The spring wood is in grcntcr state of disorganization than thc autumn wood. i n tiic m t i i i r i i i auod llic ordcriy ;iri.nngment of the stria is preserved to some extent, wliile in tlic more disorganized spring wood the striations have been distorted but an orderly micellar structure is & o m . I n longitudinal, as well as in tangential sections of the mine fragment, the entire walls are shown to consist of well-segregated colloidal particles or micelles. Figure 13 shows a tangential section of another epeeimen. It is clearly shown that, although the wood is in an advanced stage of decay and contains relatively little cellulose, the micelles, even though isolated to a far greater degree, have
PzGuns 18. ’ram CROSS SECI’ION OF SUB-BITUMINOUS COAL,SHOWINGPARTOF Woooy ATTEITUSAND TIXIN LYER OF RESIN( X 1000) M i d l e e i~ woody sttritus %rehorizontal1 h a t e d pnd have retained much oi arigiod relatiomhip of wood.gut those 10 ie8w are in brusb-hoap order.
becomes a vital question. The distance between the stri:e of 0.833 micron in the cellulose fiber, and of 1 micron in wood allows for the additional lignin in wood. If the chains in the cellulosc fiber (giving rise to the stria in the cellulose fiber) consist of nquure columns, the areas of the cross section of these are 82sL or (i80,@25square millimicrons; those in wood are 100OZor 1,000,000square millimicrons. Therefore, if 68f represents the total cciluiose units in cottoii, then loof ropresents tlie total cellulose plus lignin in wood. This is about the ratio actually found. l’et’erhaps more may be learned conccrning their relatioiisliip in tlie study of progressive decay by niicroinrgarrisiris or by the removal of either the ccliulose or lignin from wood ijy chemical nietins. The clieniical changes from sound to wellrotted wood l i n e i’eeu stiidied for some time, and many data (J, 8,20, Z?, 3’)are available. The cellulose and the hemicellulose disappear rapidly in rotting wood undcr favorable conditions, whereas most of the lignin remains and becomes transformed iiito a suiistance termed “iiumins.” Well-rotted wood is largely soluble in hot solutions of alkalies and leaves but little cellulose; the solution is colloidal and generally called “humic acids.”
19. %IN CROSS SEIJT1ON OF BITUUIN~US COALFROH NO. 6 BED
FIGURE
OF ILLINOIS
( X 1000)
retained much of tfieir original relatire location. In the transverae sections they are seen to he still arranged concentrically. In the longitudinal seetion thcy are now definitely shown t o be obloiig and arrangcil in strix,, elid to end. Whereever i t was possible to nicIisiire the distauce betwecn the eoncentric rings in the trurisvcrse section, or the distances between tho stria? in the longitudinal sections, thcy were found to be one nicron as in the souud wood. The tangential walls, or those parts of walls facing tlie observer, arc now perfectly visible, and are sccn to be composed of oblong micelles.
MICELMRSTRUCTURE OF SLI(~HTLY ROTTEDWOOD
,.I hm. sections, both transverse and longitudinal, were prepared from a piece of slightly rotted coniferous wood taken from peat. Figure 10 shorvs a transverse and Figure 11 a longitudinal section. The striations appear more definite and give, to a mneh larger degree, the appearance of being formed by oblong micelles placed end to end. The farther or Oat side of the lumina of the fibers-that is, the tangentially cut part of the fiber-is no longer entirely invisible, but certain more or less defined stria are here discernible and seen to be arranged in definite spirals. The slight rotting of the wood bas changed its physical nature, and the walls at right angles to the rays of light have also become visible. MICELLAR STRUCTURE OF Woon IN MOREADVANCED STAGE OF DECAY A number of fragments of dicotyledonous and coniferous woods in a more advaneed stage of decomposition were cx-
FIGURE 20. THIN Cnoss SECTION OF BITUMINWJS COAL FROM No. 6 BED OP Iuwois, ‘rnRouGH LAYEEOF A ~ T U(X S 1000)
1040
Fitiune 21.
I N D U S T R I A L A N D E N G I N E E R I N G C I1 E R.1 I S T R Y
THINCnoss SECTION OF Bi~ummousCOAL FXOM PITTSBURGH BED
FIGURE22. 'SHIN HOnlzoNrAL SECTION COAL(x 1000)
Vol. 24. No. 9
08
PlnsBuncn
Horirontaliy micel101lart. not layered in definite plan.
If it is assumed that the mass of rotted wood is derived largely from the lignin and that the cellulose has alniost disappeared in the process of rotting, the niicelles derived from lignin still hold similar positions. In slightly rotted wood tlie structure is the same as in sound wood, except that the striation and segregation are more distinct. I11 tracing from this stage to that of thoroughly decomposed wood, the structure, or the order and arrangement of the structure, is still the same as it was in the sound or the slightly rotted \yoad. There must exist, therefore, some close relationship betwen tlie cellulose a.nd lignin. Tho structure of pine wood from wliicli the cellulose has been removed remains to be examined. The cellulose in wood may he removed without entirely destroying its strocture. Thin transverse sections, approximately 40 microns in thickness, were cut from white pine. The oils, resins, and hemicelluloseshaving been removed, the s e c t h s were Created by the well-known Scliweitzer's nietliods to remove the cellulose. After this treatment the sections had suffered considerable t e w fng, disintegration, and shrinking but were sufficiently intact for esani i n a t io n and photography. Tinder the microscope such sections have a yellow appearance and remmble sections of well-rotted coniferous wood in structure. Figure 14isaHpierer photograph of a transverse section of a white pine from which t,he cellulose has been removed by cuprammonia, so that only lignin remains. The resemblance to that of rotted wood is clearly sliown. Again it is seen t.hat the sections consist of micelles arranged much the same as in rot.ted wood and sound wood. Therefore some re l a t io nshi p must have existed between the lignin and the cellulose in order that the lignin retain the same general line-up i i i tlie ecllulosc.
ICELI LIAR STRUCTURE ox' COALAS SEEN w i m SPIEREE
LENS I ~ N I T E .The next step from rotted peat %,oodwould be to brown coal. Unfortunately no samples of brown coal were available a t the time; therefore, Korth Dakota lignite was examined instead. I t is necessary for the study with the Spierer lens to have very thin sections, or, in other words, sections thin enough to transmit enough light to be reflected by the mirror over the front lens with sufficient intensity upon the material to t e investigated. Most coal sections are much too thick, and very carefully ground thin sections are required. Thin microt,ome sections of an anthraxylon band of lignite cut in three directioils--.transversely, radially, and tangentially-to the stem, were used. Figure 15 is a Spierer photoaauh of the transvbse section of the wood structure in which the outlines of the cell s t r u c t u r e are shown. The micelles in the wall are seen to he arranged parallel or conc e n t r i c a l l y to t h e o u t s i d e b o u n d a r i e s of the cell walls. Figure 16 is a longitudinal seetion of the sanic sample. In this, the section is cut at right angles to the collapsed walls and the radial sections of a number of closely compressed cell walls are s e e n . T h e micelles are c l e a r l y s h o w n to form strk. Figure 17 shows a Spicrer photograph of the longitudinal section a t right angles to t h e s e c t i o n shown in Figure 16 and parallel to the flattened cell walls; the tangential parts of the collapsed fibersareshown. In theedgesor the radial parts of the fiber wall, the micelles appear as straight lines, but in the tangential parts (that is, between the radial parts) t,liey are arranged in spirals.
September, 1932
I N D U S T R I A L ’4 N D E N G I N E E R 1 % G C H E M I S T R Y
1031
SUB-BITUW~OUS COAL. For the study of sub-bituminous coals, ground thin sections were used. Figure 18 shows the Spierer photograph of a sub-bituminous coal from Knife River, Mont. Except that the sub-bituminous coals are denser than the lignites and that thinner sections are required, no great differences are apparent in the micellar structure. The rod-shaped micelles have a tendency to be arranged parallel to the bedding planes of the coal, but an arrangement related to the original structure has been largely retained. Rherever the micelles were arranged in a definite series of rows so that counts could be made and average distances determined, it was found that the rows of striie occupy considerably less space than ten in 10 microns. Figure 18 shows that in the particles of translucent humic matter the micelles are still arranged in a manner relative to the original plant structure. I n the central part of the figure is seen a particle of resinous matter. The micelles in this are of a different form, larger, and without any orderly arrangement. BITUMINOUS COAL. A considerable number of observations were made and photographs taken of a number of bituminous coals from different beds and from widely separated areas. The physical structure of these coals is quite similar and in general does not differ much from that of the sub-bituminous coals except that the bituminous coals are still denser and require still thinner sections. Figure 19 shows a Spierer photograph of an anthraxylon strand with well-preserved transverse cell structure from No. 6 bed coal of Illinois. The outlines of the cells and the arrangement of the micelles within the cells are well shown. The vertical striz shown in the illustration are merely the results of microscopic scratches and are thinner parts of the section in which the micelles are more highly illuminated; they have nothing to do with the micellar structure. Figure 20 is another Spierer photograph in a n attrital part of a section of the same coal. The rodlike micelles are arranged parallel to the bedding plane of the coal. Arrangements relative to remaining plant structures are evident. The micelles, however, are not everywhere arranged in an orderly fashion; here and there are areas in the section in which they are in brush-heap or chaotic order, but this is not at all common in the coals examined. Figure 21 is a Spierer photograph of a cross section of an anthraxylous-attrital layer of a Pittsburgh coal from the Edenborn mine. The micelles for the most part have a tendency to be arranged parallel to the bedding plane of the coal, I n some places the original order of the micelles in the remaining plant structure is adhered to; in others, all orderly arrangement is lost. Figure 22 is a Spierer photograph of a horizontal section of a layer of attritus of the Pittsburgh coal, including a number of microspore exines. The micellar grouping in the spores
U. S. Bureau of Mines.
METALLURGICAL IWPORTANCE OF MANGANESE. More than 90 per cent of the yearly production of manganese is consumed in steel-making processes. No satisfactory substitute has yet been found to supplant manganese in steel-making for two distinct pur oses: as a secondary deoxidizer which remains after deoxici8ation in sufficient quantities to improve the quality of plaincarbon steels, and as an alloy element in special steels wherein it imparts valuable properties peculiar only t o such materials. There are two types of manganese alloy steels of commercial importance-“pearlitic” and “austenitic.” Pearlitic manganese steels with manganese up t o 2 per cent are useful under conditions requiring greater strength and toughness than is possessed by a plain-carbon steel. Austenitic manganese steels with 12 to 14 per cent manganese and 1 to 1.5 per cent carbon have the peculiar property of surface hardening under impact or abrasion, and are extensively used where resistance t o abrasion is required, combined with great strength and ductility.
Although the United States produces 50 per cent of the total world’s production of steel, only low-grade deposits of manganese ores are available in this country. It is difficult to produce a high-grade ferromanganese (which contains approximately 80 per cent manganese) from these ores, and foreign ores are purchased for this purpose. However, various types of spiegels (containing approximately 20 per cent manganese) can be produced from domestic ores. In a recent year when the total steel production in the United States was approximately 56 million gross tons, 85 er cent of this was made in the basic open-hearth furnace. TRe average manganese content of basic open-hearth steels is approximately 0.50 per cent; hence, about 240,000 gross tons of manganese were contained in plain-carbon steels produced that year. If foreign sources of supply were cut off, low-grade domestic ores could supply as much spiegel for basic open-hearth purposes as it might prove practicable to use.
and in the translucent humic mat’ter of the coal are clearly discernible. The spores in coals are also colloidal, but their physical structure differs from that of the humic constituents, The micelles are larger, of a different shape than those of the humic parts, and generally not parallelly nor orderly arranged. Figure 23 shows the Spierer photograph of a megaspore in the coal. It shows that the surface particles only are lined up. The inner particles are in brush-heap order. Resin particles and globules are colloidal, and the arrangement of the colloidal particles or micelles is also in brush-heap order. Figure 18 shows a resin particle in a sub-bituminous coal. LITERATURE CITED (1) Ambronn, H., Kolloid-Z., 20, 173-85 (1917). (2) Bedsu, K., Heraog, R. O., Jancke, W.,and Polanyi, M.,Z. P h y s i k , 5, 61-2 (1921). (3) Bray, M. W., and Andrews, T. M., Im. ENG.CHEM.,16, 137-9 (1924). (4) Clark, G. L., I b i d . , 22,474-87 (1930). (5) Debye, P., and Scherrer, P., Nachr. kgl. Ges. Wiss. Gottingen. M a t h . physik. Klusse, 1918,98-120. and Siemann. C., Cellu(6) Freudenberg, K., Sohns, F., Durr, W., losechem., 12,263-76 (1931). (7) Gilson, E., La Cellule, 9,337 (1883). (8) Hawley, L. F., Flick, L. C., and Richards, C. A , , IXD. ENQ. CHEM.,20,504-7 (1928). (9) Herrog, R. O., J.Phys. Chem., 30,457-69 (1926). (10) Herrog, R. O., and Jancke, W., 2. P h y s i k , 3, 196-8 (1920). (11) Herrog, R. O., and Jancke, W., Ber., 53, 2162-4 (1920). (12) Heraog, R. O., and Jancke, W., 2. angeu. Chem., 34, 385-8 (1921). (13) Hess, K., “Die Chemie der Zellulose und ihrer Begleiter,” p. 35, Akademischen Verlagsgesellschaft, Leipaig, 1928. (14) Irvine, J. C., and Hirst, E. L., J. Chem. Soc., 121, 1585-91 (1922). (15) Johnson, D. C., Botan. Gar., 20,16-22 (1895). (16) Meyer, K . H., and Mark, H., Ber., 61, 593-614 (1928). (17) Meyer, K. H., and Mark, H., lbid., 64,1999-2002 (1931). (18) Nageli, C. V., “Die Starkekorner,” Zurich, 1858; Nageli, C. Y., and Schwendener, S., “Das Mikroskop,” 15’. Engleman, Leipaig, 1864 (2nd rev. ed., 1877). (19) Polanyi, M., 2. P h y s i k , 7, 149-80 (1921). (20) Rose, R. E., and Liese, M. W., J. IND.ENQ.CHEM.,9, 284-7 (1917). (21) Scherrer, P., “Bestimmung der inneren Struktur und Grosse von Kolloidteilchen mittels Rontgenstrahlen.” I n “Kolloidchemie,” by Richard Zsigmondy, 3rd ed., pp. 408-9, Otto Spamer, Leipaig, 1920. (22) Seifrir, W., Am. Naturalist, 63,410-34 (1929). (23) Seifrit, W., J. Phys. Chem., 35, 118-29 (1931). (24) Spierer, C., Arch. sci. phys. nat., 8,121-31 (1926). (25) Sponsler, 0. L., and Dore, N. H., Fourth Colloid S y m p o s i u m Monograph, 1926,174-202. (26) Staudinger, H., Ber., 64,2721-4 (1931). (27) Waksman, S. A,, and Skinner, C. E., J . Bact., 12,57-84 (1926). (28) Wehmer, C., Ber., 48, 130-4 (1915).
RECEIVED February 23, 1932. Published b y permission of h e Director, (Not subject t o copyright.)
