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 water. The concentrated solution is I prepared by using a smaller quantity of distilled water.


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.


Jandrier's Test for Cotton in Woolen Fabrics.—Wash the sample of fabric and treat with sulphuric acid (20 Be.) for half an hour on the water bath. To ] 00 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.


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.


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.