Page:A complete course in dressmaking (Vol. 12, Men's clothes & index) (IA completecoursein00cono).pdf/92

 silk.) All animal fibers are similar in chemical composition, are proteins, and therefore are similarly affected by heat, acids, alkalies, and other chemical reagents. All vegetable fibers are similar in composition, are cellulose, and react similarly toward reagents but very differently from the animal fibers. For example, strong acids weaken and destroy vegetable fibers but do not readily destroy animal fibers. Animal fibers will readily dissolve in hot alkali solutions while vegetable fibers are little affected by them. This explains many of the precautions necessary in laundering fabrics. For example, woolens and silks must be washed in a neutral soap solution, or one which contains no free alkali.

Burning Test: When testing a woven cloth, ravel out a single warp yarn and a single filling yarn and burn each of these separately, This is necessary because the threads running lengthwise may be of one kind of fiber while those running crosswise are of another. If the yarn flames and burns quickly, emitting the odor of burning wood, it is cellulose or vegetable fiber. Cotton, linen, and artifictal silk yarns all burn in this way. If it is a cotton yarn the fiber ends of the unburned portion remaining in your fingers will be