Caoutchouc, Vul′canised

Syn. Vulcanised india rubber , Mineralised i. r. , Sulphuretted i. r. The discovery of the singular action of sulphur and the mineral sulphides on caoutchouc was made by Mr Charles Goodyear, of New York, in 1842, at which date the manufacture of vulcanised india rubber may be said to have commenced. In 1843 Mr Thomas Hancock patented a proce for vulcanised india rubber in these countries, founded on that of Mr Goodyear. A sheet of caoutchouc immersed in melted sulphur absorbs a portion of it, and at the same time undergoes important changes in many of its leading characteristics. So prepared, it is no longer affected by changes of temperature; it is neither hardened by cold nor softened by any heat insufficient to destroy it. It loses its solubility in the solvents of ordinary caoutchouc, whilst its elasticity is greatly augmented, and has become permanent. The same effect is produced when sulphur is kneaded into caoutchouc in a masticator, or by means of powerful rollers, as well as when common solvents (naphtha, spirit of turpentine, .) are charged with a sufficient amount of sulphur in solution to become a compound solvent of the rubber. In these cases articles may be made of any required form before heating them for the change of condition technically termed “vulcanisation.” It is nece ary, however, for this purpose that the form should be carefully maintained both before and during the exposure to the heat. “A vulcanised solid sphere of 2 1 ⁄ 2 inches in diameter, when forced between two rollers 1 ⁄ 4 inch apart, was found to maintain its form uninjured. In fact, it is the exclusive property of vulcanised caoutchouc to be able to retain any form impre ed upon it, and to return to that form on the removal of any disturbing force which has been brought to act upon it.” (Brocked on.) Caoutchouc combines with from 12% to 15% of sulphur; the quantity of sulphur added to the naphtha paste should not, therefore, exceed 10% or 12% of its weight. The temperatures for vulcanisation by the common method range from 320° to 330°; and the period required is one hour or more, according to the temperature. A much lower temperature is, however, sufficient if the duration of the exposure is much extended or the compound ma is softened with any of the common solvents of india rubber. The proce of sulphuring, or mineralisation, is differently conducted in different manufactories. Under Mr Burke’s patent, oxysulphide or amorphous sulphide of antimony (formed by decomposing a solution of crude antimony in a lye of potash or soda with hydrochloric acid) is employed. This powder he combines with either india rubber or gutta perch a, or mixtures of them, by kneading in a “masticator” for 2 or 3 hours, and after strong compre ion in a mould whilst still warm, he exposes the ma to a steam heat ranging from 250° to 280° Fahr. The block, so prepared, is afterwards cut into sheets, . The advantages po e ed by the product are that it po e es no unpleasant odour, nor does the sulphur effloresce on its surface, as in ordinary vulcanised india rubber. Under Mr Christopher Nickel’s patent (1849) 1 part of sulphur is kneaded with 6 parts of caoutchouc, and then pre ed into moulds, as before. He also vulcanises rubber by exposing it in a cylinder heated in a steam jacket to the fumes of sulphur or to sulphuretted gases, given off from a retort connected with the apparatus. The rubber thus prepared he next subjects to hydraulic pre ure in moulds, at a temperature ranging between 220° and 250° Fahr. Small articles or sheets of india rubber may be extemporaneously vulcanised at common temperatures by simple immersion, for a minute or two, in a mixture of bisulphide of carbon, 97 1 ⁄ 2 parts, and pro to chloride of sulphur, 2 1 ⁄ 2 parts; after which they must be well washed first in weak alkaline lye, and next in pure water. Mr Parkes employs 100 instead of 97 1 ⁄ 2 parts of the bisulphide. This method is termed “cold sulphuring.” An excellent method of vulcanisation, recommended by Mr Parkes, particularly applicable to small articles, consists in immersing them for about 3 hours in a close ve el containing a solution of polysulphide of pota ium at 25° Baumé (sp. gr. 1·197), and of the temperature of 240° Fahr. It is afterwards washed in an alkaline lye, then in pure water, and dried. Among the many applications of vulcanised india rubber those connected with its elasticity and its enormous contractile power when extended are particularly striking. Under Mr E. Smith’s patent, “torsion springs” for roller blinds, door springs, clock springs, carriage springs, ., are made of it. Mr Hodges, in another patent, has availed himself of the same property as a new mechanical power. Short lengths of caoutchouc, which he terms “vulcanised power purchases,” are succe ively drawn down from or lifted to a fixed bearing, and attached to any weight which it is required to raise; when a sufficient number of these power purchases are fixed to the weight, their combined elastic force lifts it from the ground. Thus, 10 purchases of the elastic strength each of 50 lbs. raise 500 lbs. Each purchase is 6 inches long, and contains about 1 1 ⁄ 2 oz. of vulcanised caoutchouc. These 10 purchases, if stretched to the limit of their elasticity (not of their cohesive strength), will lift a weight exceeding 650 lbs. The same principle has been applied to relieve and equalise the strain on ships’ cables, especially where several boats are towing one ve el; and as a projectile force. A number of power purchases, attached to the barrel of a gun constructed to project harpoons, will exert a power, if suddenly relieved, proportioned to their aggregate forces. By similar contrivances balls may be projected 200 yards or more, and a charge of No. 4 shot can be thrown 120 yards. A bow, in which the string alone is elastic (the reverse of the usual form), has been contrived which throws a 30-inch arrow 170 yards. The last great improvement in the manufacture of caoutchouc is the discovery that by continuing the proce of vulcanisation for a longer time at an increased heat and under pre ure, a hard black substance is obtained, which can be turned in a lathe like ebony. This substance has already been applied to an extraordinary number of uses. See Vulcanite . An exceedingly useful combination of cork and india rubber has lately been introduced. See Kamptulicon .