t the same time
leaves them yellow.

Animal fibers are best bleached by immersing in an aqueous solution of
sulphurous acid or exposing them to fumes of burning sulphur.

Wet a piece of dyed worsted or silk fabric and hang it in a quart
bottle containing fumes of burning sulphur.[26] The fumes of burning
sulphur have an affinity for coloring matter--dyestuff. The fumes
(called sulphur dioxide) do not in most cases destroy the coloring
matter as chlorine does, but simply combine with it to form colorless
compounds which can be destroyed. The color can be restored by
exposing the bleached fabric to dilute sulphuric acid.

_Questions_

1. Why is it necessary that the fabric be moist in order to be
bleached by sulphur dioxide fumes?

2. What becomes of the coloring matter?

=Experiment 27--Bleaching by Bleaching Powder=

Apparatus: Porcelain dish.
Material: Piece of calico.
Reference: _Textiles_, page 148.

_Directions_

Place a quarter of an ounce of bleaching powder in a quart bottle
containing a pint of water.[27] Then place a piece of calico in the
water containing the bleaching powder. What is the effect on the
calico? Then remove cloth to another bottle filled with dilute
hydrochloric or dilute sulphuric acid. What is the effect on the
color? Then wash the whitened cloth thoroughly in water.

Why is it necessary in practice to pass cotton fabrics through two
baths in bleaching? What is contained in the first bath? in the second
bath?

=Experiment 30--Determining Style of Weave=

Apparatus: Pick glass.
Materials: Different fabrics.
References: _Textiles_, pages 56-58, etc.

Examine different samples of cloth and classify them according to the
seven standards given on pages 56-58, etc.

=Experiment 31--Determining the Size of Yarn=

Apparatus: Yard stick.
Materials: Sample of cotton, woolen, and worsted yarns.
References: _Textiles_, pages 49, 51, 52.

As yarns used in the manufacture of fabrics are of all degrees of
thickness, it became necessary to adopt some method of measuring this
thickness. For this purpose yarns are numbered, so that when the
number is known an idea of the size of the yarn may be gained. It
would seem advisable to number yarns of all kinds according to one
fixed standard, yet unfortunately this is not done. The methods of
counting yarns are many and varied. The usual method is to estimate
the yarn number by taking the number o