A Manual of the Chemistry of the Carbon Compounds

894 TBE 0BEMI8TRY OF
DEXTRIN.
This body, which 1B also called British Gum, is an amorphous white
powder or gum-like mass, which is readily soluble in water, and
occurs in small quantity in plants and in the flesh. It is obtained
by heating starch above 150°, or by exposing starch moistened
with dilute hydrochloric or nitric acid to a temperature of 110°.
Dextrin, is also formed by heating starch-paste to 70°, and adding to
it an infusion of malt, or boiling it for a short time with dilute
sulphurio acid, The active principle of malt is a ferment called
" Diastase," of whioh a very small quantity is sufficient to convert a
very large quantity of starch into dextrin. By the further action of
diastase or sulphuric acid upon dextrin, it assimilates water, and
is converted into dextrose,
Hexouxtyl-deztrin Ctfiu(kCMiO)fit, is obtained by heating dextrin
or starch with acetyl anhydride to 160°; it ia a white amorphous body,
insoluble in water, but soluble in glacial acetic acid, and yielding
again dextrin by the action of alkalies,
GUMS,
The name gum is used to designate a number of bodies occurring
in many plants; they are all amorphous, more or less soluble in
water, and insoluble in aloohol; on boiling them with dilute
sulphurio acid, they are converted intti a glucose.
Qv/m-arabic and gwrn-senegal are the produce of different kinds of
acacia. They form colourless or yellow rounded irregular masses,
which are more or less transparent, and dissolve in water to a thick
viscid solution. These gums cousist of the potash and lime compounds
of AvaJrins To prepare this oompound, a little hydroohlorio
acid ia added to a solution of gum-arabio, and the arabin precipitated
by alcohol, It is a white, amorphous, tasteless mass, which when
dried at 100° has the composition piaHMOw + HgO} at 150° it
becomes anhydrous. Nitric acid oxidizes it to mucic and saccharic
acids, When arabin is heated with dilute sulphurio acid, it is converted
into araMnose CaH,8Op, a non-fermentable sngar, crystallizing
in rhombio needles, and turning the plane of polarization strongly to
the right.
Cerasin is the insoluble part of the gum of the oherry-tree and
plum-tree, and is also found together with arabin in beet-root; it forms
with cold water a thick, mucilaginous liquid. A similar substance is
gvm-tragaeaiUh,
Mucilage occurs in many plants, as in the kernels of the quince,
in linseed, in salep /the roots of orohis species), in the root of the
»Msh-jnallow, &e.; its is soluble in cold water, forming a thick, more
bv loss opaque liquid,