Oil test

—(linen vs. cotton); a sample of cloth is boiled in water or alkali solution to remove the finishing matter, then laid on a gla plate and saturated with a heavy oil. A smaller gla plate is then placed over the sample to protect it from the air. After removing the surplus oil from the edges, the sample is examined with the light falling on it, and then with the light pa ing thru it. The linen fiber, owing to its thick cells with their greater resistance to light, appears transparent and resembles a slop of grease on paper. When the light pa es thru it, it appears bright; and when the light falls upon it, it is dark. The reverse is the case with cotton. The air in the interior of the cotton fiber, as well as between the fibers themselves, is not displaced by the oil, and makes the cotton appear opaque; consequently when the light falls on the fiber it is bright, and when the light pa es thru it it is dark.