CARBO-HYDRATES.
319. Carbon and Water.--Some very important organic compounds
have H and O, in the proper proportion to form water, united with
C. The three leading ones are sugar, C12H22O11 or C12(H2O)11,
starch, C6H10O6, or ?, and cellulose, C18H30O15 or ?. Note the
significance of the name carbo-hydrates as applied to them.
320. Sugars may be divided into two classes,--the sucroses,
C12H22O11, and the glucoses, C6H12O6. Sucrose, the principal
member of the first class, is obtained from the juice of the
maple, the palm, the beet and the sugarcane; in Europe largely
from the beet, in America from cane. Granulated sugar is that
which has been refined; brown sugar is the unrefined. From the
sap evaporated by boiling, brown sugar crystallizes, leaving
molasses, which contains glucose and other substances. Good
molasses has but a small percentage of glucose. To refine brown
sugar it is dissolved in water, a small quantity of blood is
added to remove certain vegetable substances, after which it is
filtered through animal charcoal, i.e. bone-black, a process
which takes out the coloring-matter. The water is then evaporated
in vacuum-pans, so as to boil at about 74 degrees and to prevent
conversion into grape sugar. By this process much glucose or
syrup is formed, which is separated from the crystalline sucrose
by rapidly revolving centrifugal machines. Great quantities of
sucrose are used for food by all civilized nations. A single
refinery in New York purifies 2,000,000 pounds per day.
321. Glucose, or invert sugar, the principal member of the second
class, consists of two distinct kinds of sugar, --dextrose and
levulose. These differ in certain properties, but have the same
symbol. Both are found in equal parts in ripe fruits, while
sucrose occurs in the unripe. Honey contains these three kinds of
sugar.
Sucrose, by the action of heat, weak acids, or ferments, may be
resolved into the other two varieties. C12H22O11 + H2O = C6H12O6
+ C6H12O6. No mode of reversing this process, or of transforming
glucose into sucrose is known. Glucose is easily made from starch
or from the cellulose in cotton rags, sawdust, etc. If boiled
with dilute H2SO4 starch takes up water and becomes glucose.
C6H10O5 + H2O = C6H12O6.
CaCO3 is added to precipitate the H2SO4, which remains unchanged.
State the reaction. The product is filtered and the filtrate is
evaporated. Much glucose is made from the starch of corn and
potatoes.
322. Starch is found in all plants, especially in grains, seeds,
and tubers. Green plants--those containing chlorophyll--
manufacture their own starch from CO2 and H2O. These chlorophyll
grains are the plant's chemical laboratories, and hundreds of
thousands of them exist in every leaf. CO2 and a very little H2O
enter the leaf from the air, H2O being also drawn up through the
root and stem from the earth. In some unknown way in the leaf,
light has the power of synthesizing these into starch and setting
free O, which is returned to the atmosphere.6 CO2 + 5 H2O =
C6H10O5 + 12 O. As no such change takes place in darkness, all
green plants must have light. Parasitic plants, which are usually
colorless, obtain starch ready-made from those on which they
feed.
323. Uses.--Glucose is used in the manufacture of alcohol and
cheap confectionery, and in adulterating sucrose. It is only two-
thirds as sweet as the latter. The seeds of all plants contain
starch for the germinating sprout to feed upon; but starch is
insoluble, and hence useless until it is converted into glucose.
This is effected by the action of warmth, moisture, and a ferment
in the seed. Glucose is soluble and is at first the plant's main
food.
Commercial starch is made in the United States chiefly from corn;
in Europe, from potatoes. Differences in the size of starch
granules enable microscopists to determine the plant to which
they belong.
324. Cellulose, or woody fiber, is the basis of all vegetable
cell walls. Cotton fiber represents almost pure cellulose. From
it are made paper and woven tissues. In paper manufacture, woody
fiber is made into a pulp, washed, bleached, filtered, hot-
pressed, and sometimes glazed. Parchment paper, vegetable
parchment, is made by dipping unglazed paper for half a minute
into cold dilute H2SO4, 1 part H2O, 2 1/2 parts H2SO4, and then
washing. The fiber, by chemical change, is thus toughened. The
cell walls of wood are impure cellulose; hence the inferior
quality of paper made from wood-pulp. Paper is now employed for a
large number of purposes for which wood has heretofore been used,
such as for barrels, pails, and other hollow ware, wheels,
etc.
325. Gun-cotton is made by treating cotton fiber with H2SO4
and HNO3, washing and drying. To all appearances no change has
taken place, but the substance has become an explosive compound.
326. Dextrin, a gummy substance used for the backs of postage
stamps, is a carbo-hydrate, as in fact are gums in general.
Dextrin is made by heating starch with H2SO4 at a lower
temperature than for dextrose.
327. Zylonite and Celluloid. -These two similar substances embody
the latest use of cellulose in manufactured articles. For
zylonite, linen paper is cut into strips two feet by one inch,
soaked ten minutes in a mixture of H2SO4 and HNO3, a process
called nitration, washed for several hours, then ground to a fine
pulp, and thoroughly dried. It is then similar to pyroxiline.
Aniline coloring-matter of any desired shade is added, after
which it is dissolved by soaking some hours in alcohol and
camphor, the liquid is evaporated, and the substance is kneaded
between steam-heated iron rollers, dried with hot air, and
finally subjected to great pressure, to harden it, and cut into
sheets. Zylonite is combustible at a low temperature, and when in
the pyroxiline stage, explosively so. Ivory, coral, amber, bone,
tortoise shell, malachite, etc., are so closely imitated that the
imitation can only be detected by analysis. Collars, combs,
canes, piano-keys, and jewelry, are manufactured from it, and it
can be made transparent enough for windows.