Dilute alkalis have little effect on cotton and linen, but strong alkalis cause the fibers to swell and become yellow, and the cloth to contract. The fiber, however, is not weakened unless the alkali is allowed to remain a long time upon the cloth or to become very concentrated through evaporation. Wool and silk, on the other hand, are yellowed or destroyed by strong alkalis even in dilute solutions. Even if the fiber is not affected by the alkali, the color may be changed or destroyed. It is important, therefore, to neutralize alkali spots at once. Any of the following agents may be used:
2. A mild acid. Apply the acid with a cloth until the fabric changes back to its original color, or until the stain is slightly acid as shown by the odor or sour taste. Then rinse the fabric thoroughly in water. In the case of colored goods it is helpful to rub the stain dry, using a piece of the same material as the stained fabric, if possible. Use either of the following mild acids:
(a) Lemon juice. Squeeze the juice on the stain. As long as the spot remains alkaline the juice is a bright yellow in color, but when the spot becomes acid the color disappears almost entirely. Apply the lemon juice until this color change takes place.
(6) Vinegar. If the vinegar itself leaves a spot, remove it by sponging with water.