168

QUANTITATIVE AC.R.K'VLTUHAL ANALYHIH

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Krober's table, page 1G7, gives the weights of furfural, pentosea and pen to-
sans for weights of phloroglucide between 0.03 and 0,30 gin. For weights
less than 0.03 gm, use the following formulas:

Furfural =0.5170 (a -f 0.0052), (1)

Pentosos = 1.0170 (a + 0.0052), (2)

Pentosans = 0.8940 (a -f 0.0052), (3)

where a = weight of phloroglueide and 0.0052 represents weight of phloro-
glucide soluble in the 400 cc of acid solution.

Galactans.-—These are substances of unknown constitution
which, like the pentosans, are widely distributed in the vegetable
kingdom. Agar-agar is one of the important members of this
group. Another is the principal carbohydrate of the soybean.
When the galactans are hydrolyxed by adds they yield galaetose,
a sugar having the same empirical formula as dextrose, and nitric
acid further converts this into mucic a<wl,(Vl4(OH)4((K)OH)2.

The galactans are of considerable importance in feeds. They
are said to be utilizable to the extent of 50 per cent by herbivo-
rous animals, but agar-agar only 8 to 27 per cent by man.1

Determination of Galactans.—-Prepare* roagcmts an follows:

(a) Ammonium Carbonate, ASV>/M#0w.—Dissolve* 2 gin of ammonium
carbonate in 38 cc of water and add 2 eo of concerntrated ammonium
hydroxide.

(b) Nitric AcwZ.—Prepare, 250 cc of nitric, acid, specific gravity 1.15.
Extract an accurately weighed sample of about 2.5 gm on a hardened

paper, with five successive portions of 10 cc each of ether, place the insoluble
residue in a beaker, about .5.5 em in diameter and 7 cm deep, together with
00 cc of nitric acid (b) and evaporate the solution to exactly one-third of its
initial volume in a water bath whose temperature in 94" to !H>". After
Htanding for 24 hours add 10 cc of water and allow to stand another 24
hours. The mucic acid has, in the meantime, crystallized but. it is mixed
with other material only partly oxidized by the nitric* acid. Filter, waifh
with 30 cc of water to remove a« much of the nilru' acid aw poHHihlc* and
replace the filter and contents in the beaker. Add 30 ce of ammonium
carbonate solution (a) arid heat the mixture on a water bath at 80° for 15
minute**) with constant stirring.

The ammonium carbonate reacts with the mucic acid, forming soluble
ammonium rnueate. Wash the filter paper uwl contents Hcvc*nil timen with
hot water by decantation, pausing tin* washings through the filter paper, to
which finally transfer the material ami thoroughly wawh. Evaporate the
filtrate to dry ness on a water bath, avoiding unnecessary heating (which
causes decornposition), add 5 cc of nitric acid (fr)f stir the mixture thoroughly

XSAIKI, /. Bid. Chem.., 2, 251 (1906).

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