THE CHEMISTRY OF RUBBER 81 



insoluble substance contains a considerable amount of 

 oxygen. More recently Spence has demonstrated that 

 a large proportion of nitrogen is present in the insolu 

 ble constituent, and he regards the latter as consisting 

 mainly of protein. 



Rubber slowly absorbs oxygen on continued exposure 

 to the air with the formation of a brittle resinous substance 

 which is known as Spiller's resin, from the name of its 

 first investigator. 



Action of Heat on Rubber. — When rubber is heated at 

 temperatm-es above 100° C. it softens and becomes sticky, 

 tlie effect increasing with rise of temperature, and it 

 afterwards retains these characters on cooling. If heated 

 to a higher temperature, it melts to form a dark brown 

 liquid, which on fm'ther heating (above 160° C.) undergoes 

 decomposition with the production of a mixtiu"e of liquid 

 hydrocarbons. The liquid thus obtamed is a good 

 solvent for rubber. 



The destructive distillation of rubber, with the pro- 

 duction of this mixture of hydrocarbons, was first carried 

 out by Barnard in 1833, and since that date the products 

 of the reaction have been carefully investigated by a 

 number of chemists. From the liquid obtained by con- 

 ducting the distillation at the ordinary pressure, the 

 following hydrocarbons have been isolated : 



Isoyrene (CsHg, boiling-point 37°-38° C), which was 

 first separated and examined by Greville Williams in 1860. 



Dipentene (CioHis, boiling-point 180°-181° C.) was first 

 obtamed in 1835 by Hmily, who called it caoutchine, 

 and was afterwards examined by Greville Williams. In 

 1879 a hydrocarbon (di-isoprene), possessing similar char- 

 acters to caoutchine, was obtained by Bourchardat by 

 heating isoprene in a sealed tube, and later Wallach 

 showed that this hydrocarbon and caoutchine were 

 identical with dipentene. 



Harries has separated two other hydrocarbons from the 

 dipentene fraction of the distillate, one boiling at 147°- 

 150° C. and the other at 168°-169° C. 



Heveene. — Bourchardat gave this name to an oil which 

 he separated from the fraction of the distillate boiling 

 above 200° C, but it has never been carefully investigated. 



It may be mentioned that Fischer and Harries have 

 found that if the distillation of rubber be conducted in a 



