3. What is the burning test for animal fiber?

Repeat the same experiment, placing the untwisted yarn in sulphuric acid. Apply heat and note the effect.

What is the acid test for vegetable fiber?

What is the acid test for animal fiber?

Examine different fabrics to see whether they contain vegetable or animal fibers.

=Experiment 45--Difference between Cotton and Linen Fabrics=

Examine a real linen towel and a cotton towel. Wet your hands and use both towels to dry them. Notice which of the fabrics absorbs the moisture quicker, or which towel dries the hands better.

Compare a cotton table-cloth and a linen table-cloth. Notice that the linen fabric has a natural gloss, a cool, smooth feel, and launders much better than cotton. The cotton fabric on the other hand gives off a fuzz, and irons dull and shapeless.[29]

Linen is tough and strong, cool feeling, and has a long fiber. Linen cannot be given a cotton fabric finish.[30]

Cotton on the other hand has a weak, short fiber, dull, warm, and non-absorbent. After washing, cotton resembles a limp rag while linen retains firmness and stiffness.

Which fabric absorbs the moisture more readily?

What is the difference in appearance between the two fabrics? Between the fibers of the fabrics?

=Experiment 46--Test to Distinguish Artificial Silk from Silk=

Apparatus: Porcelain dish, pota.s.sium hydrate.

Material: Piece of silk fabric.

Reference: _Textiles_, page 240.

Since silk fabrics, particularly hosiery, are becoming popular, various attempts have been made to produce subst.i.tutes for real silk.

To test a silk fabric, boil the sample in 4 per cent pota.s.sium hydrate solution and note the effect. If it produces a yellow solution it is artificial silk, if colorless it is pure silk.

Another simple way used by some workmen, although unhygienic, is to unravel a few threads of the suspected fabric, place them in the mouth, and masticate them vigorously. Artificial silk will soften under the operation and break up into a ma.s.s of pulp. Natural silk will retain its fibrous strength.

Test various samples of cheap "silk" hosiery.

=Experiment 47--Test to Distinguish Silk from Wool=

Apparatus: Porcelain dish, hydrochloric acid.

Material: Silk or woolen fabric.

Reference: _Textiles_, page 240.

Silk may be distinguished from wool by putting the suspected thread or fabric into cold concentrated hydrochloric acid. If silk is present it will dissolve, while wool merely swells.

Test various samples of silk and wool.

=Experiment 48--Test to Distinguish Cotton from Linen=

Apparatus: Fuchsine, ammonia.

Materials: Cotton and linen fabrics.

Reference: _Textiles_, page 240.

_Directions_

1. On account of the high price of linen various attempts are made to pa.s.s cotton off for linen. While it is possible sometimes to detect cotton by rolling the suspected fabric between the thumb and finger, the better way is to stain the fabric with fuchsine. If the fibers of the fabric turn red, and this coloration disappears upon the addition of ammonia, they are cotton; if the red color remains, the fibers are linen. The most reliable test is to examine the fiber under the microscope and note the difference in structure.

2. Test a cheap _linen_ fabric for cotton.

3. When cotton yarn is used to adulterate linen it becomes fuzzy through wear, and when used to adulterate other fabrics, it wears shabby and loses its brightness. Linen is a heavier fabric, and wrinkles much more readily than cotton. It wears better, and has an exquisite freshness that is not found in cotton fabrics.

4. Describe a chemical test for linen.

5. What is the difference in appearance and wearing qualities of cotton and linen?

=Experiment 49--Test of Fabric to Withstand Ironing and Pressing=

Apparatus: Hot iron.

Materials: Silk, cotton, and woolen fabrics.

_Directions_

Place the sample over an ironing board and iron it with hot iron (about 200 F.). Compare the sample immediately with one not ironed.

Remember that many colors, particularly colored silks, change while they are hot. If the original shade returns when the fabric has cooled, then the fabric is fast to ironing and pressing.

_Questions_

1. What is the object of ironing and pressing clothes?

2. Is it a good plan to press clothes often?

3. Is there any difference in the effect of the hot iron on the three kinds of fabrics?

=Experiment 50--Test of Fabric to Withstand Perspiration=

Apparatus: Porcelain dish.

Materials: Silk, cotton, and woolen fabrics.

Reference: _Textiles_, page 243.