148

QUANTITAriYK AflHK'l'l/ri'ItA/, .1 .Y.IM'.S'/X

cell walls. Lignin also is a collective name; applied to the ^in-
crusting substances'7 formed with cellulose as the plant matures.

Determination of Crude Fiber.-—Prepare the following .solutions:

(a) Sulphuric Acid, 1.25 per cent (0.255 normal) as determined by
titration against a fifth-normal base.

(b) Sodium Hydroxide, 1.25 per cent (0.3125 normal). This solution

should be practically free from sodium enr-
onate. Use sodium hydroxide sticks that
have been purified by alcohol. Titrate
against a standard acid and adjust.

Use the residue from the ether extrac-
tion, page 147, or extract a fresit dry sample*
(2 gin) with ether, using the apparatus
already described. Rinse the residue into
a 250-cc wide mouth flask connected with a
return condenser (Kig. 42j, then add 200eeof
sulphuric acid (a), previously heated to
boiling. Boil gently for '10 minute**. After
this time remove the residue from the* flask
and filter the liquid through an alundunt
cup, using suction. Wash the cup find
contents until free from acid. Wash the
residue from the cup buck into the flask
with 200 cc of boiling sodium hydroxide (/;)
and boil for 30 minutes. Filter through an
alunclum cup us before and wash free from
base. The cup is dried at 11(1' to constant*
weight, then the residues IH burned and the
per cent, of fiber calculated from the IOHH in
weight. A linen filter may be used instead
of an alundurn cup, in which case rinse the*
washed fiber into a flat platinum dish by
means of a stream of water; evaporate to
dryncss on a steam bath, dry to constant
weight at 110°, weigh, burn the organic
matter and weigh again. The loss in weight
is crude fiber. If a weighed paper in uned
instead of alundum or linen, weigh in a
weighing bottle. In any cane the* crude
fiber after drying to constant weight at 110° must be burned and the loan
of weight determined.

Optional Method.1—Proceed as above until the acid extraction i» com-
pleted. Neutralize the sulphuric acid without filtration, using 10-per cent
sodium hydroxide and phenolphthalein. Add 200 cc of 2.6-per cent solution

lOhioExp. *S7a. Bull, 256 (1913).

FIG. 42.—-Apparatus for crude
fiber determination.