STUDIES ON CELLULOSE BY EDWARD G. P.XRKER
The statement is made in text-books that cellulose is distinguishable by its non-reactivity to ordinary reagents. Methods of analysis start upon this assumption, removing the non-celluloses by more or less drastic means, leaving the basal fiber or cellulose itself untouched. The portions which are removed are either hydrolyzed or oxidized, thus being rendered soluble. Excepting the elementary analysis of cellulose, there is in n o method a complete reaction. Since hydrolysis and oxidation are not separate and distinct actions each due t o definite reagents, but are rather parallel and coexisting with nearly all reagents used, it seems better t o divide analytical methods for the determination of cellulose into A. Those depending upon acids. B. Those depending upon bases The general reactions involve oxidation and solution where acids are employed, hydrolysis and solution where bases are used. The normal cellulose is least subject to those influences and remains as a fairly inert residue. It is, however, undoubtedly attacked to a certain extent, being converted, a t least superficially, into oxy- and hydrocellulose, as shown : chemically by reaction with Fehling’s solution ithe CO group of oxycellulose), and the fixation of basic aniline dyes (methylene blue) ; physically by a change from long fiber with definite microscopic characteristics, to a more or less finely divided powder and short brittle fiber, depending upon the extent of the attack. Under (A) there are mainly the methods of Schulze’ (nitric acid and KC10, a t 15’ for 12 to 14 days); 1Iuller’ (bromine in diffused daylight a t z o o for 2 to 3 days); Cross and Chem. Zentralblatt, 321 (1S5;).
” Die Pflanzenfaser,
27, 28.
220
Edward G. Parker
Bevan' and modification of Dean and Tower' (chlorine). These are based upon the main fact of oxidation and ultimate breaking down of the cellulose molecule completely. It therefore becomes a matter of choice, where any of them is to stop, and where the measure of the reaction is to be taken. This is especially true of methods depending upon the halogens, which invariably give lower results than those depending on the action of alkalies which follow, and upon which this work is based. Under ( B ) we have mainly the methods of: Lange3 (water and alkali, fusion a t 180') ; Honig4 (glycerine a t I IO') ; Gabriel' (glycerine and alkali; a combination of Honig and Lange methods); and the a'eender process' or crude fiber method, which is most iyidely used, for the determination of fiber in plants and foodstuffs. I t depends primarily upon the alternate action of dilute alkali IKOH) and dilute acid IH,SO,). I t is perfectly true that all methods for the isolatioii of normal cellulose are more or less arbitrary, and even slight deviations from procedure, in time, concentration, or temperature will affect materially the results obtained. It is evident, nevertheless, that the nearer we approach pure cellulose the slower the reaction becomes, leading us to believe that it is the non- and lignocellulosic constituents which give reactions their impetus and that when pure celldose is reached a considerable period of time may elapse before the attack is recommenced. lye propose to show this in our work, by means of a modification of Lange's' method. Lange's original method is as follows: Cross and Bevan: Cellulose, 95. Jour. Chem. SOC.,29, 1119(190;). Zeit. physiol. Chem., 14,217 (1989). Chem. Ztg., 14, 868, 902 (1890). Zeit. physiol. Chem., 16,2 7 0 (1891). Holdefleiss: Landxirtschaftl. Jahrbiicher, Suppl., Band 103 (1887) Zeit. physiol. Chem., 14,283 (1889): 16,z j o (1891).
Studies
OH
Cellulose
221
"Ten grams of the original substance are placed in a large, deep, tubulated retort with 3-4 times its weight of pure KOH, and about 30-40 cc of H 2 0 . This is then closed with a glass stopper, and heated in an oil bath. The temperature is measured by a thermometer placed in the bath. the bulb being on a lei-el ivith the bottom of the retort. ,It about r-+o0, with considerable foaming, boiling begins. The temperature then rises little by little to about 180'. The heating is COIItinued for about one hour. The foaming is then finished, aiid the mass falls together in the retort, then melts and finally dries. End of reaction. The retort is iion- taken frcm bath, the contents, after cooling to about S o c C , are taken up ivitli hot n-ater and ir-ashed carefully, first ivith repeated xts1iiIig-s n-ith hot n-ater, and. finally, into a beaker ir-ith cold n-ater. -After cooliiig, the solution is acidified with dilute H.,SO,, \\-hereupon immediately a thick flocculent precipitate is formed consisting of small particles of cellulose, 11-hich had remainecl suspended in the strong alkali. Upon acitiification the cellulose is precipitated out quantitati\-ely. The contents of the beaker are non- made slightly alkaline by the careful addition of S a O H , so that all the precipitated substance Ir-ith the exception of the cellulose goes again into solution. The solution is non- filtered with strong suction, through a sieve-like, fine-perforated, platinum cone. The residue left on the filter is washed first with hot and then with cold n-ater, taken from the filter, and digested with alcohol, again filtered, and washed with ether, and finally dried and weighed. By ignition of the residue and subtraction of the n-eight of the product obtained, the pure cellulose content is obtained. ' ' I n a later modification Lange' substituted a porcelain crucible 6 j cm high for the retort and a centrifugal for suction, thus cutting down the time of operation from six to tn-o and one-half hours. This method has given widely varying results irr the hands of different investigators, and, while i t may give comparable Zeit. angew. Chem., 19,561 (1895).
Edward G. Parker
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results on different substances, slight variations of conditions (temperature and time), when used on the same substance, affect the results obtained to a considerable extent. I n Table I are some of the results obtained by J. J. Frank (of this University) with the method of Lange on pure cotton (Red Cross surgeon's absorbent cotton) : TABLE
__
I.-j
GRAXS COTTO;*r
AND 2 0
GRAXSKOH
~~
Time Hours I I I
I
Temp.
H*O Grams
180'.
I00
180'-2
IO' ISO"
L
40
I
