_Directions_
1. In addition to withstanding the action of coming in contact with the human skin, fabrics like hosiery, etc., should withstand the excretions of the body.
2. To test a fabric for resistance, place the sample in a bath of dilute acid made by adding one teaspoonful of acetic acid to a quart of water warmed to the temperature of the body, 98.6 F. The fabric should be dipped a number of times, and then dried, without rinsing, between parchment paper.
_Questions_
1. What is the effect of the acid solution upon the fabrics?
2. Would they necessarily withstand the effect of perspiration, even if they did withstand the acetic acid solution? Why?
=Experiment 51--Test for Determining Dressing=
Apparatus: Magnifying glass, porcelain dish.
Materials: Various fabrics.
Reference: _Textiles_, page 242.
_Directions_
1. A great many cotton fabrics such as muslin often contain considerable sizing or dressing. In order to examine a fabric and determine whether too much dressing has been used, take a small sample of the fabric and crush it in the hand and rub it together, so that the dressing is removed and the quantity employed may be determined.
If much dressing has been used, dust will be produced in rubbing.
Prick the surface with your finger nail. Notice whether the starch comes off. Then wet your finger and rub it on the cloth and allow it to dry. Does the gloss disappear?
2. Another method is to hold the sample before the light and notice whether you can recognize the dressing. Examine the sample with a magnifying glass (or pick glass) and notice whether the dressing is superficial or penetrates the substance of the fabric.
3. Would you buy low priced cotton goods with a thick gloss and pasty look?
4. Notice the effect (lusterless) of fabrics containing much dressing after washing.
5. A very simple way for telling the amount of loading or weighting in a cotton fabric is to weigh a given sample, then "boil the fabric out in hot water,"--boiling for several hours and then drying it. The difference in weight after drying and before boiling gives the weight of sizing material per sample piece.
6. If mineral loading has been used to a great extent, a large residue is left after burning.
=Experiment 52--Testing the Strength of Cloth=
Apparatus: Dynamometer.
Materials: Various fabrics.
Reference: _Textiles_, page 237.
_Directions_
1. An excellent way to test the strength of a fabric is to place the two thumbs together and press them down on the sample, holding it tight underneath. Then try to break the threads, first in one direction and then in the other. Do they break easily? Notice whether one set is very much stronger than the other.
2. Manufacturers usually test yarn and fabrics by means of an instrument called a dynamometer. In this way one can find out whether a yarn or fabric comes up to the necessary strength, and whether it has the required yield or stretch. Both these points are of importance in practical work, for it is essential that the yarn as shown should at least be strong enough to bear the strain of manufacture. The test is made by stretching a hank of yarn between the two hooks of a cloth testing machine. The handle at the side is now turned, so that the lower hook descends and puts a strain on the hank. This strain is increased, and at the same time the pointer moves around the dial, which indicates in pounds the amount of strain. When the threads of the hank begin to break, the strain is released, and the catch at the side keeps the pointer in position until the amount of strain is read on the dial. The distance stretched by the yarn before breakage occurs is shown in inches and fractions of an inch, in the small indicator arranged near the upper hook.
Test different fabrics and yarns.
=Experiment 53--Characteristics of a Knitted Fabric=
Apparatus: Pick glass.
Materials: Knitted fabric, woven fabric.
Reference: _Textiles_, page 153.
_Directions_
1. Examine a piece of knitted fabric under the pick glass and notice the construction. How does it differ from weaving? The single thread is formed into rows of loops which hang upon each other, thus giving the knitted fabric its characteristic springiness. Why is hosiery suitable for underwear? Try to obtain the thread of the knitted fabric and reduce the whole to a heap of yarn by cutting it. Is the yarn intact?
2. A knitted fabric may be told from a woven fabric by studying the following sketch. (See page 310.)
Note that the element of stretch or elasticity is wholly lacking in the woven cloth except what lengthwise elasticity may be in the threads themselves. On the other hand, referring to the printed diagram of the knitted fabric it will just as readily be seen that its very structure implies such a corrugation of its individual loops that if distended by force in any direction its tendency is to return to the normal.
The essential characteristics of good hose are:
1. That they should be without seams.
2. That they should be so knit as to conform to the foot of the wearer.
3. That they should be thickened or reinforced where the greatest wear comes.
[Illustration: ORDINARY WEAVING
_a._ Weft. _b._ Warp.]
[Illustration: PLAIN STOCKING FABRIC]
The essential characteristics of good underwear are:
1. It should be made from elastic cloth, which implies a knitted cloth.
2. It should be porous in a high degree--whether in winter weight or summer weight.
3. The seams should be made upon the most modern sewing machines, with as little bulk as possible.
=Experiment 54--Experiment to Illustrate Imperfections in Hosiery=
Apparatus: Magnifying glass.
Materials: Hosiery (seconds).
Reference: _Textiles_, page 159.
Examine a piece of hosiery called a _second_, obtained from a hosiery mill, and notice whether any of the following defects are present: