VULCANISATION 83 



ozone forming a substance belonging to the group of 

 compounds which he has termed ozonides. A study of 

 the decomposition products of this caoutchouc ozonide 

 has thrown an interesting Hght on the question of the 

 constitution of the hydrocarbon. 



Vulcanisation. — ^The vulcanisation of rubber may be 

 effected by dipping it in melted sulphur, by heating a 

 mixture of rubber and sulphur, by treating rubber with 

 a solution of sulphur monochloride, or by exposing it 

 to the vapour of sulphur monochloride. In the second 

 method the rubber is mixed with a certain proportion 

 of sulphiu", varying in practice from 4 to 40 per cent., 

 according to the class of product required, and is then 

 heated at a temperatiu-e usually rangmg from 125° to 

 150° C. Only a portion of the sulphm- actually combines 

 with the rubber, the excess remaining in the vulcanised 

 product as free sulphm*. In this process the combination 

 of the sulphur with the rubber is greatly facilitated by 

 the presence of certain substances; such as litharge, 

 slaked hme or magnesia. 



In vulcanising by means of sulphur chloride the rubber 

 is treated with a solution of this reagent in benzene, 

 containmg from 1-5 to 3 per cent, of sulphur chloride, 

 or in special cases the rubber is exposed to the vapour. 



Experiments conducted by Weber led him to the 

 conclusion that vulcanisation is brought about by a 

 chemical change, the caoutchouc combming with the 

 sulphur or sulphur chloride to form addition compounds 

 such as CioHisSoCls. More recently, however, it has 

 been suggested by Wolfgang Ostwald that the taking up 

 of sulphur or sulphur chloride by rubber is more probably 

 a case of coUoidal adsorption than of chemical change. 

 The discussion as to which of these views best represents 

 the laiown facts is still proceeding and it is recognised 

 that a combination of both actions may be involved. 



Constitution of Caoutchouc. — The hydrocarbon caout- 

 chouc has the empkical formula CioHig, bemg thus similar 

 in composition to oil of turpentine and other terpenes, 

 but at present its molecular weight is unknown and con- 

 sequently its molecular formula can only be expressed 

 as (CioHie)^. It is an optically-inactive, unsaturated 

 hydrocarbon, each CioHig group containing two unsatu- 

 rated linkages and therefore capable of forming addition 

 7 



