he starch
granules, being microscopic in size, readily pass through the cloth with
the water, and may be caught in any suitable container. The starch is then
allowed to settle to the bottom, the water poured off and the starch
collected and dried.

Starch is insoluble in water; but if boiled in water, the granules burst
and a slimy opalescent mass, known as "starch paste," is obtained. This is
undoubtedly a colloidal suspension of the starch in water. By various
processes, such as boiling with very dilute acids, treatment with acetone,
etc., starch is converted into "soluble starch" which dissolves in water to
a clear solution. Soluble starch is precipitated out of solution by
alcohol, or by lead subacetate solution.

Air-dried starch contains from 15 to 20 per cent of water; but this can be
completely removed, without altering the starch in any way, by heating for
some time at 100 deg. C.

The starch granules from different sources vary considerably in size and
shape, and can generally be identified by observation under the microscope.

The most characteristic reaction of starch is the blue color which it gives
with iodine. The reaction is most marked with starch paste or soluble
starch, but even dry starch granules are colored blue when moistened with a
solution of iodine in water containing potassium iodide, or with tincture
of iodine.

When hydrolyzed, either by boiling with dilute acids or under the influence
of enzymes, starch undergoes a series of decompositions, yielding first
dextrins, then maltose, and finally glucose. These transformations can be
traced by the iodine color reaction, as starch will show its characteristic
blue, dextrins purple or rose-red, and maltose and glucose no color with
iodine.

=Dextrins= may occur in plants as transition products in the transformation
of starch into sugars, or _vice versa_. Most commonly, however, they are
artificial products resulting from the partial hydrolysis of starch in the
laboratory or factory. They are amorphous substances, which are readily
soluble in water, forming sticky solutions which are often used as
adhesives ("library paste" is a common example of a very concentrated
preparation of this kind). They are precipitated from solution by alcohol,
but not by lead subacetate (distinction from starch). They are strongly
dextrorotatory (specific rotatory power +192 deg. to +196 deg.); are not
fermented by yeast alone, but readily undergo hydrolysis to gl