CHAPTER XV. 

 VULCANIZATION AND USES OF RUBBER. 



Vulcanization of rubber — Heat, sulphur, and indiarubber — The heat 

 cure and cold cure — Quantity of indiarubber in common articles 

 — Rubber in roller coverings, steam packing, tyres, tobacco pouch, 

 and garden hose — High proportion of mixtures — Automobiles , 

 instruments, clothing, and cables — Disuse of rubber and usp of 

 substitutes. 



A CREAT part of the rubber industry is dependent upon the 

 il. material being in a vulcanized condition, the change being 

 effected by mixing sulphur in one of its many forms with the masti- 

 cated rubber and then heating the mixture. Usually only from 4 to 

 ."> per cent, of sulphur is used in ordinary vulcanization, but in the 

 production of ebonite or vulcanite as much as 20 to 40 per cent, of 

 sulphur- may be used. A more complete distribution of sulphur 

 through the indiarubber may be possible if a solution containing 

 sulphur be added to the latex before coagulation. Prismatic 

 sulphur is readily soluble in carbon bisulphide, benzene, ether, &c, 

 and solutions may be made with any of these and other reagents to 

 contain varying amounts of sulphur. 



The main factor upon which the action between sulphur and india- 

 rubber depends is heat ; there is no action between the two consti- 

 ( uents until the temperature is equal to or above that of boiling water, 

 and in Europe a temperature varying from 125° to over 300° C. is 

 commonly used in the process of vulcanization. If alkaline poly- 

 sulphides are used, vulcanization can be effected at temperatures 

 little above 100° C. 



In this process a great part of the sulphur becomes fixed by the 

 indiarubber, but not the whole of it ; there is always a certain quan- 

 tity of the sulphur in a free state in vulcanized articles of commerce. 

 Ordinary sulphur, or various compounds of sulphur, may be used in 

 this process, and the articles manufactured from such material are 

 usually considered to be tougher, more resistent, and less easily 

 melted. 



The Heat and Cold Cures. 



Rubber may be vulcanized cither by what is known as the heat 

 cure or the cold cure, [n the heat cure the rubber and sulphur are 

 mixed together by machinery and the temperature raised to 300° E.. 



