297. To Detect Cotton in Linen

297.    To Detect Cotton in Linen. Take a small piece of the cloth, boil in water and dry; then take 3 parts, by weight, of sulphuric acid, and 2 parts of crushed nitrate of potassa; put the dry piece of cloth in this mixture for 6 or 7 minutes, and then wash it in water until there is no taste of acid; dry it at a gentle heat; next put it into a mixture of ether and alcohol, which will dissolve the cotton and not the linen. If the piece be weighed before and after putting it into the ether and alcohol, the quantity of cotton in the fabric can be accurately ascertained.

298. To Distinguish Cotton and Wool

298.   To Distinguish Cotton and Wool. Take a small piece of the cloth and boil in caustic soda; the wool will be dissolved, and the cotton remain. If the threads have been previously counted, their relative mixture can be found.

299. To Detect Cotton with Silk or Wool

299.    To Detect Cotton with Silk or Wool. Put a piece of the cloth into chlorine water or bleaching liquor. The cotton is whitened, and the silk and wool turn yellow, and can easily be distinguished by the aid of a pocket lens.

300. To Detect Cotton in Silk or Wool

300.  To Detect Cotton in Silk or Wool. Take a small piece and unravel the threads, and inflame them; the cotton burns away freely and leaves little or no black charcoal; the wool and silk shrivel up, leave a black charcoal, and give a strong smell.

Decidedly the best and safest method, and one applicable in all cases, is a microscopic examination, by which not only the structure, but also the nature of the fibre can be demonstrated. Cotton, wool and silk are easily distinguished by the microscope, as they differ materially in appearance. Cotton forms flat, narrow ribbons, curled up in spirals like those of a corkscrew; wool fibre is stouter than all others, and may be recognized by its scaly surface, while silk is the thinnest fibre, has the smoothest surface, and possesses the least structure. These appearances.are very characteristic, and any one who has observed them once will ever afterwards recognize them again at first sight.

301. To Distinguish Silk and Wool in Fabrics

301.   To Distinguish Silk and Wool in Fabrics. Silk can always be identified in a mixture with any other animal or vegetable fibre by means of concentrated hydrochloric acid, which dissolves it completely and immediately, without appreciably affecting any woolen or woody fibre with which the silk may have been interwoven. Strong sulphuric acid has also a powerful solvent effect upon silk, and is likewise much more destruc-tive in its action upon cotton than the other acid. Should it be desired to determine the nature of any fibres remaining after the solution of the silk, it is first necessary to wash and collect them, when they will usually be found destitute of color. To decide whether wool is present or absent, a s61ution of picric acid may be employed, which instantly imparts a full yellow tint to the wool, but does not in the least affect cotton, linen, or China grass; so that it is only necessary to immerse the fabric in the dye, wring it out, and wash well with water. Should, any portion remain of a yellow color, the presence of wool is indicated. Other methods can be employed similar in principle, but the picric acid is believed to be best. Discrimination between the different kinds of fibre can best be prosecuted by means of the microscope, but their quantity is best found by dissolving away one fibre, as already directed, and weighing.