Page:A complete course in dressmaking (Vol. 12, Men's clothes & index) (IA completecoursein00cono).pdf/93

 brushlike—its fibers tending to separate. If it is a linen yarn the fiber ends remain closely in contact.

If a yarn burns with difficulty, emitting a very disagreeable odor like burning hair or feathers, it is protein, or animal fiber. Wool and silk both burn in this way. A woolen yarn as it burns rolls up, forming a little ball at the end; silk, unless it ts weighted with metallic salts to make it appear of heavy quality, does the same thing. If the silk yarn is heavily weighted with metallic salts, it not only does not roll up but there remains after the burning a white or gray ash.

Boiling-Out Test: The presence of cotton or other vegetable fibers in a woolen cloth or yarn is determined by a boiling-out test. When cotton is carded with wool in the same yarn it is often impossible to tell by the appearance or by burning that the cotton is there. A very simple chemical test will reveal its presence. Dissolve one ounce of caustic potash or caustic soda or a tablespoonful of lye in a pint of water. Boil a small sample of the cloth in a little of this solution for fifteen minutes. The wool will dissolve but cotton, if present, will remain. Strain the solution