CAOUTCHOUC 703 



He remarks that bags of such cloth made with a thin coating of rubber, soon eva- 

 porated sufficient -water to cause mildew, when laid upon each other ; but this slow 

 evaporation does not interfere with their ordinary applications. 



The porosity of caoutchouc would appear to explain the readiness with which it is 

 permeated by different liquids which have no chemical action upon it. Thin sections 

 of dry caoutchouc of the best kinds absorb from 18 to 26 per cent, of water in the 

 course of a month, and become white from having been brown. It is, however, found 

 that endosmose action is constantly active in India-rubber. In tubes through which 

 gas flows there is always some escape of hydrogen deprived of much of its carbon. 



To enumerate the applications of these double fabrics for cushions, life-preservers, 

 &c., beds and boats, would be out of place here. 



For single-texture fabrics, or cloth with one side only prepared, the process is the 

 same as that described for double fabrics, only that one side only is proofed, or covered 

 with India-rubber solution or paste ; and this kind of waterproof has an advantage 

 over the old, that the surface worn outside, being non-absorbent, imbibes no moisture 

 and requires no drying after rain or wear. The objection to single-texture fabrics, 

 of being liable to decomposition by the heat of the sun and from close packing, has 

 been obviated by a discovery adopted by Messrs. Warne and Co., termed by them 

 the Sincalor process (sine calore, without heat) ; by which the properties of the rubber 

 are ^ so changed that heat, grease, naphtha, and perspiration, which decompose the 

 ordinary India-rubber waterproof, in no way affect the waterproof goods of the 

 ' Sincalor ' process. The singular changes effected by this process are especially 

 shown by the application of a hot iron to the surface, which destroys it without the 

 usual decompositions ; the substance is burnt, but is not rendered sticky. The process 

 is stated to be secret. 



IV. VtJI-CANISATION. 



Of all the changes effected by chance, observation, or chemical experiments of late 

 years, few cases have been so important as the change in India-rubber by the process 

 called Vulcanisation. The union of sulphur with caoutchouc gives new 'properties 

 so valuable, that it may be said the former well-known quality of elasticity is now 

 rendered so variable that almost every range, from the most delicate tenuity to the 

 hardness of metals, can be obtained at will by the manufacturer. These changes in 

 the caoutchouc are produced with a degree of permanence to defy air, water, saline 

 and acid solutions ; the material is incapable of being corroded, and more permanent 

 under harsh usage than any other set of bodies in the world. Such are the results of 

 the processes that induce a ' change ' in caoutchouc when sulphur and heat are em- 

 ployed; where metals and minerals are employed, 'metallised' and 'mineralised,' 

 ' thionised,' and a number of other terms have been used. 



When caoutchouc is mixed with from 2 to 10 percent, of sulphur, and then heated to 

 270 and 300, it undergoes a change, it acquires new characters, its elasticity is 

 greatly increased, and is more equable ; it is not affected nor is the substance altered 

 by cold, no climate effects a change, heat scarcely affects it, and when it does it does 

 not become sticky and a viscid mass ; if it yields to a high temperature it is to 

 become harder, and will ultimately yield only at the advanced temperature to char 

 and to decompose. All the ordinary solvents are ineffectual. The oils, grease, ether, 

 turpentine, naphtha, and other solvents scarcely alter it, and the quantity of sulphur 

 that will effect the change is known not to exceed 1 or 2 per cent. Further, if pecu- 

 liar solvents, such as alkalies, remove all apparent sulphur from it, still the change 

 remains ; indeed, the analogy of steel to iron by the changes of condition effected by 

 some small quantities of other bodies seems to be an analogous condition. Whatever 

 the theory, which is exceedingly obscure, still the practice, by whatever name, is to 

 obtain this changed state and exalted elastic properties. 



' Vulcanisation ' was discovered in America. Mr. Goodyear relates, that having 

 made a contract for India-rubber mail bags, they softened and decomposed in service, 

 and while he thought a permanent article had been made, the colouring materials 

 and the heat, united to soften and to destroy the bags ; hence, by this failure, dis- 

 tress of all kinds arose, and the trade was at an end. During one of the calls at the 

 place of abandoned manufacture, Mr. Goodyear tried a few simple experiments to 

 ascertain the effect of heat upon the composition that had destroyed the mail-bags, 

 and carelessly bringing a piece in contact with a hot stove, it charred like leather. 

 He called the attention of his brother, as well as other individuals who were present, 

 and who were acquainted with the manufacture of gum elastic, to the fact, as it was 

 remarkable, and unlike any before known, since gum elastic always melted when 

 exposed to a high degree of heat. The occurrence did not at the time appear to them 



