INDIARUBBER MANUFACTURES.
Under the term "indiarubber manufactures," will be included a description of the manufacture of those articles in which indiarubber or caoutchouc, guttapercha, and some allied exudations are largely employed. For an account of the raw materials, the reader ie referred to the article on Resinous Substances.
The name "caoutchouc " in England is generally confined to the pure hydrocarbon forming the greater portion of ordinary indiarubber ; its composition, according to Faraday, is represented by the formula The chemical and physical properties of this substance extend more or less to the commercial kinds of rubber, and, in proportion as a sample of rubber approaches the qualities of pure caoutchouc, its commercial value increases. The internal portions of beat Para, "bottle" ru'obcr, when dried in the dark, are sufficiently pure for any practical examination of the substance. The amount of the pure principle contained in any given sample may be ascertained by dissolving in highly rectified ether, and precipitating with alcohol, which should be repeated for a high purification. Ether containing alcohol, does not dissolve caoutchouc at all. Caoutchouc readily oxidizes on exposure to the air, becoming brown on the surface, which is blackened and rendered rotten by extreme oxidation. This coloration is removed by alcohol or alcoholized ether. Long digestion of masticated rubber, in alcohol, renders it quite colourless ; but it becomes sticky, and, on exposure to the air, rapidly darkens in colour. Caoutchouc is soluble in ether, chloroform, carbon bisulphide, coal-tar naphtha, benzol, turpentine, and in almost any liquid hydrocarbon ; incorporated with solid hydrocarbons, as naphthalene, or paraffin, it behaves under the influence of heat in the same way as a true solution. It is insoluble in water, alcohol, and acid and alkaline solutions; but is rapidly acted upon by strong mineral acids, especially when heated, and by chlorine, bromine, and iodine in the cold. Heated above 4° (40° F.), it is soft and elastic, and remains the same at 100° (212° F.); below 4° (40° F.), it is hard and inelastic, but not brittle ; when heated to 115° (239° F.), it softens, and is decomposed into a sticky, tarry masa by standing for a few days ;
congelation prevents this only while it lasts : heat accelerates the change. In this condition, how ever, it may be vulcanized. By destruotive distillation, it yields a series of liquid hydrocarbons, which have been employed as solvents for caoutchouc, as lubricators, &c. They do not possess any particular interest, although a study of them might furnish very important information as to the synthetic production of this or similar hydrocarbons ; the substances known as " artificial rubber," &c., are widely different in composition from caoutchouc. Contact with oily or fatty substances induces the decomposition of caoutchouc. Its sp. gr. is 0.925-0.950. On incineration, it should yield only an insignificant amount of ash. In commerce, the manufactured article is frequently called " rubber " or " indissubber " ; when cured or vulcanized, it is called "vulcanized rubber," if soft ; and " vulcanite " or "ebonite," when cured to a hard or horny condition. Raw indiarubber as met with in the markets is technically called " gum." The best descriptions, in order of purity, are the Brazilian, Central American, Asiatic, and African. There are many applications, where the inferior kinds, irrespective of their being oheaper, are better adapted than the finer descriptions. Part rubber yields a hard and strong material when vulcanized, but is always contaminated with the taste and smell of the raw product. Negrohead has a still more unpleasant taste and smell when vulcanized, and is softer.
The preliminary treatment of all kinds of rubber is much the same as regards sorting, washing, and drying; there is, however, a great difference in carrying out the details of these processes, according to the nature or condition of the rubber, some deacriptions having to be cautiously heated and dried, whilst others are much more eaaily manipulated. In selecting raw rubber, preference should be given to packages made up of small masses, or thin pieces, and to those samplea whioh, when cut and squeezed, emit little or no moisture; bark and chips are more abundant in the drier kinds.