402 BULLETIN OF THE BUSSEY INSTITUTION. 
on neutralizing the alkaline solution, that the colloid wood gum is 
thrown down. 
I can myself bear witness that it happens occasionally when an 
alkaline solution of wood gum is acidulated that no great amount 
of precipitate will appear until after the lapse of some time when 
a mass of it will fall all at once as if from a supersaturated solu- 
tion. Gudkow,* when working upon wheat bran and the excre- 
ment of a bran-fed pig, noticed that while considerable quantities 
of pentosans could be dissolved from these materials by dilute 
potash lye no precipitate was produced on acidulating the alkaline 
solutions. Hoffmeister ¢ in his turn encountered this difficulty and 
insisted that the addition of alcohol to the acidulated liquid is 
necessary in order to insure complete precipitation of the gum. 
Once down, the precipitate might be washed with cold water, but, 
as Hoffmeister has said, in order to avoid loss a sufficient quantity 
of aleohol must be added at once, at the time of neutralization. 
In any event, wood gum, even that prepared by Thomsen’s method 
can hardly fail to contain more or less of the lignic acids of 
Lange and of the ‘‘ cellulose gum” of Hoffmeister. For the rest, 
it is notorious that wood gum distilled with hydrochloric acid gives 
less furfurol than should be given if the material were pure xylan, { 
and that less xylose than theory requires is yielded by wood gum 
when subjected to hydrolysis. § 
Here follows a statement of results obtained jn several instances in which 
impure wood-gum was precipitated in the rough manner suggested by Loew. 
Kind of Wood. Per cent of wood gum in wood dry at 100° C, 
Inner Wood. Outer Wood. Bark. 
Gray Birch felled in May ... . 14.29 14.41 ; 
ee . moe October. = 5 45.04 13.54 6.77 
Sugat Maple 457] (Re sie (eee Me 4.48 
Alder felled in January ..... 19.36 15.00 11.83 
Date Stones s5-52% ads 94h. oii eipedeel yh > 8.85 
Cellulose. Several estimations of the ‘‘ cellulose” in the woods 
under examination made by the Weende method — which consists 
essentially in acting upon the powdered wood with hot dilute acids 
and alkalies used alternately — gave the following results : — 
* Zeitschrift fiir Chemie. 1870 [N. F.], 6, 362, 364. 
+ Landw. Jahrbiicher. 1888, 17. 251. 
t Flint and Tollens, Versuchs-Stationen. 42, 406. 
§ Tollens, Handbuch der Kohlenhydrate. 2, 202. 
i i ay 
