Part 12 (1/2)
[7] The change is empirically represented as
C_{6}H_{12}O_{6} + HBr - 4H_{2}O = C_{6}H_{5}O_{2}Br.
SECTION IV. CELLULOSE GROUP, INCLUDING HEMICELLULOSES AND TISSUE CONSt.i.tUENTS OF FUNGI
VERSUCHE ZUR BESTIMMUNG DES GEHALTS EINIGER PFLANZEN UND PFLANZENTEILE AN ZELLWANDBESTANDTEILEN AN HEMICELLULOSEN UND AN CELLULOSE.
A. KLEIBER (Landw. Vers.-Stat., 1900, 54, 161).
~ON THE DETERMINATION OF CELL-WALL CONSt.i.tUENTS, HEMICELLULOSES AND CELLULOSE IN PLANTS AND PLANT TISSUES.~
In a preliminary discussion the author critically compares the results of various of the methods in practice for the isolation and estimation of cellulose. The method of F. Schulze [digestion with dil. HNO_{3} with KClO_{3}--14 days, and afterwards treating the product with ammonia, &c.] is stated to be the 'best known' (presumably the most widely practised); W. Hoffmeister's modification of the above, in which the nitric acid is replaced by hydrochloric acid (10 p.ct. HCl) is next noted as reducing the time of digestion from 14 days to 1-2 days, and giving in many cases higher yields of cellulose. The methods of treating with the halogens, viz. bromine water (H. Muller), chlorine gas (Cross and Bevan), and chlorine water, are dismissed with a bare mention, apparently on the basis of the conclusions of Suringar and Tollens (_q.v._). The method of Lange, the basis of which is a 'fusion' with alkaline hydrates at 180, and the modified method of Gabriel, in which the 'fusion' with alkali takes place in presence of glycerin, are favourably mentioned.
These methods were applied to a range of widely different raw materials to determine, by critical examination of the products, both as regards yield and composition, what t.i.tle these latter have to be regarded as 'pure cellulose.'
This portion of the investigation is an extension of that of Suringar and Tollens, these latter confining themselves to celluloses of the 'normal' groups, i.e. textile and paper-making celluloses. The present communication is a study of the tissue and cell-wall const.i.tuents of the following types:--
1. Green plants of false oat gra.s.s (_Arrhenatherium, E._).
2. Green plants of lucerne (_Medicago sativa_).
3. Leaves of the ash (_Fraxinus_).
4. Leaves of the walnut (_Juglans_).
5. Roots of the purple melic gra.s.s (_Molinia caerulea_).
6. Roots of dandelion (_Taraxac.u.m officinale_).
7. Roots of comfrey.
8. Coffee berries.
9. Wheat bran.
These raw materials were treated for the quant.i.tative estimation of cellulose by the method of Lange (b), Hoffmeister (c), and Schulze (d), and the numbers obtained are referred for comparison to the corresponding yields of 'crude fibre' (Rohfaser) by the standard method (a).
As a first result the author dismisses Lange's method as hopeless: the results in successive determinations on the same materials showing variations up to 60 p.ct. The results by c and d are satisfactorily concordant: the yields of cellulose are higher than of 'crude fibre.'
This is obviously due to the conservation of 'hemicellulose' products, which are hydrolysed and dissolved in the treatments for 'crude fibre'
estimation. A modified method was next investigated, in which the process of digestion with acid chloroxy- compounds (c and d) was preceded by a treatment with boiling dilute acid. The yields of cellulose by this method (e) are more uniform, and show less divergence from the numbers for 'crude fibre.'
The author's numerical results are given in a series of tables which include determinations of proteids and ash const.i.tuents, and the corresponding deductions from the crude weight in calculating to 'pure cellulose.' The subjoined extract will ill.u.s.trate these main lines of investigation.
___________________________________________________________
Crude Fibre
Pure Cellulose
_____________
____________________________
Raw Material
Weende
Hoffmeister
Hoffmeister,
Method.
Method.
modified by
(a)
(c)
Author.
(e)
________________
_____________
_____________
______________
Oat gra.s.s
30.35
34.9
31.5
Lucerne
25.25
28.7
20.5