ii2 SCIENCE PROGRESS 



thiozonides of aromatic amines are relatively stable substances 

 which would therefore not act readily as sulphur carriers ex- 

 plains the observation that aromatic amines cannot be em- 

 ployed in place of aliphatic amines. The practical importance 

 of these observations lies in the fact that by lowering the 

 temperature at which vulcanisation can be effected it becomes 

 possible to incorporate with the rubber various organic colouring 

 matters which would not stand the ordinary vulcanising 

 temperature without decomposing. Experiments have also 

 been carried out on the vulcanisation of rubber by means of 

 other substances such as the halogens or ozone in place of 

 sulphur. In the former case a halogenide of the rubber is 

 formed in the first instance and this substance is then adsorbed 

 by the unchanged rubber which thereby undergoes vulcanisa- 

 tion. With regard to oxygen it has been shown that if rubber 

 is exposed to moist air at the ordinary temperature it becomes 

 covered with a film of less elastic material . If such rubber is 

 then passed through rollers in order to make it as homogeneous 

 as possible and is subsequently heated it becomes vulcanised, 

 whereas, if the less elastic outer layer is removed before heating 

 no vulcanisation ensues. It follows from this that the vulcanis- 

 ing agent in this case is the material formed by the action of 

 the oxygen upon the rubber. From the widely different 

 chemical nature of the various substances which can be em- 

 ployed for vulcanising it may be concluded that the change 

 is a purely physical one, depending on the formation of a col- 

 loidal substance with the rubber which is then able to bring about 

 the transformation. The process may in fact be compared with 

 the conversion of cellulose esters into collodion by the addition 

 of camphor which takes the part of the vulcanising agent. 



The change undergone by rubber on exposure to moist air 

 is compared by the author to the so-called drying of certain 

 fatty oils. It is of course a well-known fact that highly un- 

 saturated oils on exposure to air become converted into viscid 

 liquids or varnish-like solids, for which reason such oils are 

 known as drying oils. That the change was in some way 

 connected with the absorption of oxygen was proved some time 

 ago, quantitative measurements having shown that an oil may 

 absorb as much as 24 per cent . of its weight of oxygen . Several 

 authors have drawn attention to the fact that volatile products 

 are given off during the process, but the nature of these sub- 



