Values of the three constants. K, A, and B,have been determined for the products from the Pennsylvania and California crudes. An interesting similarity in form may be noted in the curves obtained by plotting values o € these constants against the upper distillation limits of the respective cuts from the two types of crude. 7-Present results have failed to indicate any reliable genera1 method of calculating viscosity-temper~,.‘,urecurves of oils for which less than three experimentally determined points are arailable.
Binoham. “Criticism of Some Receu; Yixo . Inyescignxions.” J Chem. Soc., 103 (19131, 950. Thole, Mussel and Dunstan s c a s i t y I L a x i p a snci Their Ioterpretation,” J . C l i e v ~ . ~ , S ~ .103 c . , (1913), 11 Flowers. Viscosity lleasurrmPnt, a n d a h-em T-isrosirneter,” Pnrc. .47n. SOC.Test. Alalerialsz,, 14 (1914 Anonymous,,, hbaolute ter,” EnGineerinR 100 (131.5) 254. Dubrisay. Method of the ‘iiscosity oi LubricotiT$ Oils,” J . SOC.Cheni. I n d . , 36 (1917) Hersrhel. “Determinaticn of Absolute Visco by tho Saybolt Universal and the E n g l ~ Visco5imeters,” r Proc. .4m. S o t . T F C ITInteriaZs, ~. 17 (19171, 11,551, Lidstone. “A Mercurial 1-iscosimeter,” J . Soc. Chem. Ind., 36 (1917).
.
9713 ?,I
_.”(
I
Sheppard. “The Measurement of the Absolute Viscosity of Very Viscous Media,” J . I n d . f l n g . Chem. g (191i) 523. Bingham. “Variable Presswe ?;lethod for the Measurement of Viscosity,” Proc. ilm. S O C .Teef. Mate&k, 18 (1916>,11, 3 i 3 . Ringham and Jackson. “Standard Substances for the Calibration of Viscoaimeters,” Bureau of Staqdards, Scientific Paper, 298. Dunstan and Thole. Relation between Viscosity and the Chemical SHORTBIBLIOGRAPHY 267. Constitution of Lubricating Oils,” Petroleum Res., 38 (1918), 24;: Herschel. “The Standard Saybolt, Cniuersal Viscosimeter, Proc. Am. Girard. Memoirs de l’acodemie d f s Sciences, 1816. Soc. Test. Materials, 18 (1918): 11, 363. Poiseville. Reczieil des Savants Eiratzgers 1842;A n n . chim. p h y s . , 131 7 A-icolardot and Baume. The Dubrisay Method of Examining Lubricat(1843), 50 Couette. “Studies on the T-iscosity of Liquids,” Q ? I L chin,. phyi.., (61 ing, Oils” Analyst, 43 (1918), 226. Nicolardot and Baume. Contribution t o the Study of the Viscosity of 21 (1890), 433. Lubricating Oils,’:,Chimie & i n d u s t v i e , I i1918), 265. Thorpe and Rodger. “Relation between the l’iscosit,y of Liquids and Oelschlager. The Viscosity of Oils, 2. V e r . deut. I n g . , 62 (1918), 422. Their Chemiral S a t u r e , P h i l . Trans. -4., 185 (1894), 397. Thorpe. “Viscosity of Pure Liquici?,” Science Progresr, IZ (1918), 583 Thorpe and Rodger. “The Viscosity of Mixtures of Nisrible Liquids,” Faust. “Visrosity Measurements 2. physik. Che,nz., 93 (1919),, i58. J . Chem. Soc., ,?I (18971, 360. Herschel. “Standardimtion of the Saybolt liniversal Viscosimeter,” Beck. Beitrage cur relatiyen Innern Reibung,” 2. p h y s i k . Chem., Bureau of Standards TechnoZgic Paper I I Z (1919). 58 (1907), 425. Herschel. “Viscosity of Gasoline,” Bureau of St>andards, Tcchnolgie Dunstan and RTilson. “Relation between Molecular Weight and 7%Paper I25 (1919);‘ , cosity of a Series of Compounds,” J . Cliem. S o c . , g1,(1907j,90. 1.awaccek. \iscosity and I t s Meesur@ment,” 2. I e r . deut. Ing., 6.3 Dunstan and eo-workers. “Viscosity of Liquid Mixtures,” J . C h e m (1919), 677. Sac., 85 (19041, 817; 87 (1905), ?,l;91 (19071, 83. S t a n ; y . “Determination of the Absolute 1-isc0sitic.s of Liquids at High Dunstan and co-workers. Relation between Viscosity xiid Cheniicnl Pressure E?zgineering, In8 ,(1919), 520. Constitution,” J . CRem. SOC. 93 (1908),,1918; 95 (190?), 15#?6. Herkhel. “The MacRlichBel Torsion Viscosimeter,” J . I d . E n g . Chem., Findlay. Viscosity of ‘Binary hIixtures a t Their Boiling Points,“ Z. 12 (19201, 817. physik. Chem., (1909), 203. Herschel. “Saybolt Viscosity of Blends,” Bureau of Standard@,TeciiBingham. Viscosity a n d Fluidity,” A m . C h r m . J . . 35 (1906), 195; 40 nica2 Paper 364 (192G). (1908), 277; 43 (19101, 2%. Schwedhelm. “The Viscoaity of Oils and Other Liquids a s a Function Dunstan and Strerens. “The Viscosity of Lubrirating Oils,” J . S O C . of the Temperature,” Chem.-PlQ.. 4 5 (1321), 41. Chem. I n d . , 31 (19121, 1063.
9,
The Effect of Chemical Reagents on the Microstructure of Wood’’2 By Allen Abrams RhSE4RCH LABORLTORI O F APPLlBD
CHE\IISTRY,
11 9SSkCHLSETTS
I n connection with research work on paper being carried by this laboratory for the Mead Research Company of Dayton, Ohio, it became desirable to secure an insight into the changes occurring in the structure of wood during various chemical treatments. Consequently, an in.r.estigation was undertaken, as a result of which a method was developed and made use of in carrying out such treatments. A number of reagents have been studied, and while the results here presented must be regarded as preliminaq and incomplete, it is hoped that they may stimulate further work along similar lines by other investigators. The most obrious method f o r studying the effects of reagents on the microstructure of wood would be to treat blocks of the wood with these reagents a t the desired temperatures and pressures for specified lengths o € time. The wood might then be sectionecl and studied either under the microscope o r by means of photomicrographs. Unfortunately, however, the mechanical difficulties of sectioning such wood are so great that, even with the most skilful technique, it is apparently impossible to make sections without altering the anatomical structure. F o r this reason it has been necessary t o develop a new procedure, which consists essentially in first making thin sections of wood and treating these with reagents under the proper conditions. In order that the changes produced by these chemical treatments may be comprehended, it is first desirable to note the three planes in which wood may be sectioned-a cross or tl-awwerse section is one cut perpendicular to the axis of the t r u n k ; a radial section is one cut longitudinally along the radius of the trunk; a tangential section is one cut longitudinally, tangent to the rings of growth and there1 Presented before the Section of Cellulose Chemistry a t the 61st Meeting of the American Chemical Society, Rochester, N. T...4pril 20 to 29. 1921. ‘Published as Contribution X o . 34 from the Research Laboratory of Applied Chemistry, Massachusetts Institute of Technology.
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T B C H N O L OCi\IBR C~,
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fore, perpenaicular to the radius of the trunk. Figs. 1,Zy 3 are, respectirely, cross, tangential, and radial sections of pine.
CELL STRUCTURE The process of plant growth is essentially that of cell division whereby each cell in the growing region (the ‘‘ cambium ”) is split into two daughter cells. The partition separating these cells is known as the “ middle lamella ” (Fig. 4 ) . As growth continues, other walls are laid clown adjacent to the middle lamella and nearer Ihe hollow interior (‘( lumen ”) of the cell. The complete facts connected with cell growth are extremely complicated. To the paper-maker, however, the important fact is that any chemical process f o r making paper should have for its primary object the separation of individual cells by dissolving out the middle lamella with as little effect as possible on the remainder of the cell wallll. To be sure, another very important action is that of decomposing compound celluloses, such as lignocellulose, and thus producing a pure cellulose. The history of the cell walls and the study of their chemical structure have been the subjects of extensive research, conducted usually, however, by men with botanicaI rather than chemical training. The -results of these investigations3 show that the middle lamella should be regarded as the primary partition wall, serving to bind the tracheids together; but at the same time, i t must be understood that this layer has a complicated history in which it undergoes changes in form, mass and chemical composition. Allen‘ is certain that the middle lamella differs chemically from the later walls. He believes that the first formed cellular wall consists essentially of pectin-like substances 1 C.E. Allen, Bot. Ga
., 33 (19011, 1.
S e p t , 1921
T H E J O U R N A L OF Ih’DiYSTRIAL ‘72 T\’D E N G I N E ER ILVG CH E J I I S T R Y
which are plastic, and therefore undergo such changes in form as are necessary to adapt the layer readily to alterations occurring in the cells during growth. As the cells grow older, the middle lamella becomes more rigid and inflexible, until finally it assumes a hard, insoluble form. This process is believed to consist in a transformation of the pectic acid originally present into an insoluble material, probably calcium pectate. Aside from the mineral constituents of the cell wall, the most important substances are compounds (probably of a n adsorption type) of cellulose, such as lignocelluloses and pectocelluloses. Cross and Bevanl compare the lignocellulose structure to a n alloy of a base and a noble metal, in which the more reactive base metal may be dissolved out by suitable methods, leaTing the comparatively inert noble metal. I n a similar way, cellulose is comparatively resistant to the action of reagents such as chlorine, alkalies, o r bisulfites, all of which tend to remove the lignin groups. Konig and Rump,2 a f t e r an extensive chemical and microscopic study, conclude that there are no true compounds of cellulose and other substances in the cell, but that these materials exist here intimately mixed. Spaulding3 has made a n extensive study of cellulose and lignin in various woods. From this he concludes that, whereas cellulose and lignin are generally intimatelr mixed in the cell wall, yet in some woods a ring of pure cellulose lines the aell lumen. Moreover, this cellulose is found especially in those cells which do not contain starch, and Spauldiiig coneus with Sablon’s4 previous work on willow, in which Sablon had been led to believe that starch was converted into cellulose. While there is considerable controversy over the subject, it seems probable that the formation of lignocellulose is a process of thickening by incrustation : colloidal, hydrated celluloses are first formed, and they then take u p lignin held in colloidal solution in the sap.5 These changes follow quite closely upon one another, since heart wood and s a p wood give about the same yields of cellulose and lignocellulose.0
For the purpose of these considerations, it may then be assumed that the cellular structure is composed largely of intimate mixtures of loose o r adsorption compounds of cellulose -dh lignin and pectin, and the hemicelluloses. The cell walls are largely made u p of compounds of lignin and cellulose, while the middle lamella is probably coiiiposed largely of pectocellnloses and hemicelluloses. On account of the fact that these substances are present in a colloidal condition, changes in the individual units cannot be followed by the ordinary microscopic methods. It is only where such changes are expressed in the more extensive structural alterations that the microscope is of value. Staining with dyes which affect only certain portions of the moody structure has long been the subject of controversy, since some observers advance evidence to show that staining distinguishes mere physical changes in the degree of colloidal dispersion rather than chemical diffeerences in ’the structure, while other observers take the opposite viey. As a matter of fact, it is comparatively unimportant which view we adopt when staining is used in following the 1 “Wood Pulp and Its Uses,” 1911, 30. 2 N a h r . Genussm., 28 (1914), 4. 3 Missouri Botanioal Garden, Report 1906,41. 4 Reu. Gen. Bot.. 16 (1904), 362. 5 Wislicenue, A o c h b l . P p t r f u b , 41 (1910),845. 6 Statement, Foreet Products Laboratory.
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changes produced by reagents on a given structure. It is not unreasonable to believe that such chemical and physical changes go hand in hand and that they are both distinguished by staining. From all the available information it would appear that in cooking wood with various chemicals in aqueous solution, one or more of the following changes is likely to take place : 1-Hydration of the constituents, naturally accompanied by swelling. 2--Depolymerization, or an increase in the degree of colloidal dis ersion, of the various woody substances. 8 0 t h of these effects are slow and progressive and both are accelerated toward complete peptization or colloidal solution of the constituents as the time, temperature or concentration of the solut,ion is increased. 3-Actual hydrolysis of the constituents, accompanied generally by true solution. 4-Other fairly definite cheirdcal reactions, such as chlorinntion, oxidation or sulfonation of constituents, followed by colloidal or true solution. The reagents used in analytical or practical work on cellulose and lignin are naturally chosen because of a more or less selective action on one of these substances. I n such cases a knowledge of the changes in microstructure which accompany these reactions should throw some light on what is taking place.
METI~OD OF MAICIXG WOODSECTIOSS Starting with the tree itself, small blocks of wood (1in. X 0.5 in X0.5 in.) are cut from the portions of the trunk to be studied. These blocks are boiled vigorously in water for about an hour, 0.r until they sink. The air is thus driven out of the tracheids and is replaced by \yater. With the Thomson microtome these blocks may be cut at once ; but with other microtomes it is generally necessary to soften the blocks several days in cold 50 per cent hydrofluoric acid to dissolve out mineral constituents such as silica. According t o Jeffrey,l hydrofluoric acid does and attack the middle lamella. On the other hand, its use should be dispensed with wherever possible, as it undoubtedly hydrolyzes some constituents of the wood. (All wood sections used in these experiments were macle after acid treatment.) Following the acid treatment, the block is washed tlioroughly in water and is transferred to a mixture of equal parts of ethyl alcohol and glycerol. Sections of from 20 to 40 microns in thickness a r e made from these blocks. Thinner sections are difficult t o handle during later treatments, while thicker sections a r e unsatisfactory for visual purposes. These sections a r e transferred t o 50 per cent ethyl alcohol until ready for use. Many staining reactions for cellulose and lignocellulose are described in the literature, but the combination which has proved most satisfactory f o r this work is Haidenhain’s hematoxylin and safranin. Hematoxylin is commonly supposed to stain cellulose deep purple, and similarly, safranin to stain lignocellulose red. Safranin withstands acid and alkaline treatments satisfactorily, but hematoxylin is acted upon by both; consequently sections may be stained with safranin before such treatments, but not with hematoxylin. After staining with this combination, the following structures are purplish: the resin ducts, cells of the medullary rays, tori of the bordered pits, and in some instances a thin layer of the cell wall next the lumen. The middle lamella is deep red, while the remainder of the cell wall is of a lighter red color. There is also a marked difference in the refractive indices of these structures.
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1 “Anatomy of Woody Plants,” 1917, 447.
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T H E JOURNAL OF INDUSTRIAL .4ND EXGINEERING CHEMISTRY
Fig. I-Cross section of Pine. 76. showing tracheids (cells 01 "fibers") of s p ~ i n g snd Wmma gi-owth. resin duet. and medulIxrh T B ~ S( h a w black lines)
Fig. 2-Tangential section of ~ i n c . 76. showing tracheids ("fibers") and medullar~ ram (the latter in cmas s e t i o n )
Fig. 5-Cross section of Pine. 166. trrsted with 12N hydroehleric acid for 28 hrs. at 260 C.
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Fiy. %-Radial section of pine. 76, showi n s medullary rays and tracheid8 ("fibed'i dotted with eiicular '%ordered L,its"
Fig. 6-Tanpentid seCtion of pin?. 156. threetaf with 12N hydrochloric m i d for 28 h a . at 250 C.
iater growth of cell < d l CWEMICAL TREATXEXT OF sECTIoNS
The sections were placed in the depressions of a microscope cell slidc. The cells of the slide were filled with the magent to be studied, and a plain microsoope slide was laid over the cell slide, bat separated from it about 0.1 mm. by pieces of thin cover glass. The two slides were wired together and were placed in an autoclave containing a eonsiderable quantity of the reagent. I n those cases, where the reagent attacks iron considerably (e. g., sodium bisulfite solution), the slides were sealed into glass tubes with the reagent. The tube containing the slide was then placed in the autoclave and was surrounded with water as the heating liquor. This method allowed access of the reagent to the section and yet prevented destructive rnechanieal action. I n order to follow the eoume of the treatment, several slides were introduced into the autoclave simultaneously. The antoelave was bolted shut and heated over a gas flame for various lengths of time at predetermined temperatures and pressures, measured respectively by a thermometer in a well and hy a steam gage. At stated intervals the autoclave was removed from the flame, cooled quickly and opened, and a slide was removed. The autoclave was again closed and heated for another interval of time. The treated seotions were washed carefully to remove adhering liquor and dirt. They were then stained and
mounted in balsam for microscopic esamination and m e a r urement. Photomicrographs of these sections were made with a metallnrgical microscope and camera arranged for use ayith transmitted light. I n some cases sections took the stains so poorly after treatment, or were so badly decomposed, that satisfactory photographs could not be obtained, although visual ohservations were reasonably satisfactory. Misleading optical effects due to unsatisfactory lighting sometimes occur, and mast always be guarded against. I n this investigation observations and measurements were made directly on the sections rather than on photomicrographs. Measurements have been made on the cell wall, the middle lamella, and the lumen of five representative cells in both the spring and summer wood of each section. These measurements were made in a radial direction and by the use o f a filar micrometer. Averages of the five readings were taken and compiled for study. While these results serve to interpret the action of various reagents, they are not sufficiently comprehensive to be taken as quantitative Measurements of the middle lamella are considerably less accurate than the others because of the comparatively slight breadth of this structure. The effects of various reagents have been studied nuder different conditions of concentration, time of heating, temperature and pressure. It must be borne in mind that the results of such experimental treatments, especially as far as the rate of action
Sept., lYZl
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Fix. 7 Fir. 7--Rndid section of pine. 16C. treated w i t h l2N hidroehioiic acid
