COTTON
Bleaching Of Cotton:
I.—Bleaching by Steaming.—The singed and washed cotton goods are passed through hydrochloric acid of 2° Bé. Leave them in heaps during 1 hour, wash, pass through sodium hypochlorite of 10° Bé. diluted with 10 times the volume of water. Let the pieces lie in heaps for 1 hour, wash, pass through caustic soda lye of 38° Bé. diluted with 8 times its volume of water, steam, put again through sodium chloride, wash, acidulate slightly with hydrochloric acid, wash and dry. Should the whiteness not be sufficient, repeat the operations.
II.—Bleaching with Calcium Sulphite.—The cotton goods are impregnated with 1 part, by weight, of water, 1 part of caustic lime, and 1/2 part of bisulphite of 40° Bé.; next steamed during 1–2 hours at a pressure of 1/2 atmosphere, washed, acidulated, washed and dried. The result is as white a fabric as by the old method with caustic lime, soda, and calcium chloride. The bisulphite may also be replaced by calcium hydrosulphite, and, instead of steaming, the fabric may be boiled for several hours with calcium sulphite.
III.—Bleaching of Vegetable Fibers with Hydrogen Peroxide.—Pass the pieces through a solution containing caustic soda, soap, hydrogen peroxide, and burnt magnesia. The pieces are piled in heaps on carriages; the latter are shoved into the well-known apparatus of Mather & Platt (kier), and the liquid is pumped on for 6 hours, at a pressure of 2/3 atmosphere. Next wash, acidulate, wash and dry. The bleaching may also be done on an ordinary reeling vat. For 5 pieces are needed about 1,000 parts, by weight, of water; 10 parts, by weight, of solid caustic soda; 1 part of burnt magnesia; 30 parts, by weight, of hydrogen peroxide. After 3–4 hours’ boiling, wash, acidulate, wash and dry. The bleaching may also be performed by passing through barium peroxide, then through sulphuric acid or hydrochloric acid, and next through soda lye. It is practicable also to commence with the latter and finally give a treatment with hydrogen peroxide.
The whiteness obtained by the above process is handsomer than that produced by the old method with hypochlorites, and the fabric is weakened to a less extent.
Tests For Cotton.
I.—Cotton, when freed from extraneous matter by boiling with potash, and afterwards with hydrochloric acid, yields pure cellulose or absorbent cotton, which, according to the U. S. P., is soluble in copper ammonium sulphate solution. The B. P. is more specific and states that cotton is soluble in a concentrated solution of copper ammonium sulphate. The standard test solution (B. P.) is made by dissolving 10 parts of copper sulphate in 160 parts of distilled water, and cautiously adding solution of ammonia to the liquid until the precipitate first formed is nearly dissolved. The product is then filtered and the filtrate made up to 200 parts with distilled {246} water. The concentrated solution is prepared by using a smaller quantity of distilled water.
II.—Schweitzer’s reagent for textile fibers and cellulose is made by dissolving 10 parts of copper sulphate in 100 parts of water and adding a solution of 5 parts of potassium hydrate in 50 parts of water; then wash the precipitate and dissolve in 20 per cent ammonia until saturated. This solution dissolves cotton, linen, and silk, but not wool. The reagent is said to be especially useful in microscopy, as it rapidly dissolves cellulose, but has no action on lignin.
III.—Jandrier’s Test for Cotton in Woolen Fabrics.—Wash the sample of fabric and treat with sulphuric acid (20 Bé.) for half an hour on the water bath. To 100 to 200 parts of this solution add 1 part resorcin, and overlay on concentrated sulphuric acid free from nitrous products. The heat developed is sufficient to give a color at the contact point of the liquids, but intensity of color may be increased by slightly heating. If the product resulting from treating the cotton is made up 1 in 1,000, resorcin will give an orange color; alphanaphtol a purple; gallic acid a green gradually becoming violet down in the acid; hydroquinone or pyrogallol a brown; morphine or codeine, a lavender; thymol or menthol a pink. Cotton may be detected in colored goods, using boneblack to decolorize the solution, if necessary.
IV.—Overbeck’s test for cotton in woolen consists in soaking the fabric in an aqueous solution of alloxantine (1 in 10), and after drying expose to ammonia vapor and rinse in water. Woolen material is colored crimson, cotton remains blue.
V.—Liebermann’s Test.—Dye the fabric for half an hour in fuchsine solution rendered light yellow by caustic soda solution and then washed with water—silk is colored dark red; wool, light red; flax, pink; and cotton remains colorless.
To Distinguish Cotton from Linen.—Take a sample about an inch and a half square of the cloth to be tested and plunge it into a tepid alcoholic solution of cyanine. After the coloring matter has been absorbed by the fiber, rinse it in water and then plunge into dilute sulphuric acid. If it is of cotton the sample will be almost completely bleached, while linen preserves the blue color almost unchanged. If the sample be then plunged in ammonia, the blue will be strongly reinforced.