a fabric.

=Testing the Constituents of the Warp and Filling.= Take a sample
piece of the cloth to be examined--the piece must be large enough to
contain specimens of all the different kinds of yarn present in the
material--and separate all the filling and warp threads. Be sure that
all double threads are untwisted.

=Combustion Test; Test for Vegetable and Animal Fibers.= Burn
separately a sample of the untwisted warp and filling threads. If one
or both burn quickly without a greasy odor, they are vegetable fibers,
cotton or linen. If one or both burn slowly and give off a greasy
odor, they are animal fibers, wool or silk. This test is not
conclusive, and further chemical examination--acid test--must be made
to ascertain whether wool is pure or mixed with cotton.

=Acid Test.= The vegetable fibers, cotton and linen, are distinguished
from those of animal origin by their behavior in the presence of
acids and alkalies. The vegetable are insoluble when boiled with a 4
per cent sodium hydrate solution, but readily clear or carbonize when
saturated with a 3 per cent sulphuric acid solution and allowed to dry
at a high temperature in a hot closet. Wool on the other hand is not
affected by the action of weak sulphuric acid.

=Cotton Distinguished from Linen.= If the fibers are vegetable, cotton
may be distinguished from linen by staining the fibers with fuchsine.
If the fibers turn red, and this coloration disappears on the addition
of ammonia, they are cotton, if the red color remains the fibers are
linen. Whenever cotton yarn is used to adulterate other fabrics, it
wears shabby and loses its brightness. When it is used to adulterate
linen, it becomes fuzzy through wear. One may detect it in linen by
rolling the goods between thumb and finger. Linen is a heavier fabric,
and wrinkles much more readily than cotton. It wears better, and has
an exquisite freshness that is not noticed in cotton fabrics.

=Silk Distinguished from Wool.= Place the fabric or threads containing
animal fibers in cold, concentrated hydrochloric acid. If silk is
present it will dissolve, while wool merely swells.

=Artificial Silk from Silk.= On account of the low value of the
artificial and the high value of genuine silk, there is a tendency to
offer the artificial instead of the pure article. Test: When
artificial silk is boiled in 4 per cent potassium hydrate solution it
produces a yellow solution, while pure silk gives a colorless
solution.