ON THE PRESEXT POSITION OF THE CHEMISTRY OF RUBBER. 241 



rubber. After distilling off the low boiling portions of the distillate, 

 Wallach subjected the remainder to distillation in steam, and thus ob- 

 tained a liquid boiling after rectification at 180°, the ' caoutchine ' of Himly, 

 Williams, and Bouchardat. On treatment with bromine this gave a 

 solid tetrabromide, melting-point 125°-126°, which proved to be com- 

 pletely identical with the tetrabromide of the hydrocarbon then known as 

 cinene (now dipentene). The solid hydrochloride was also obtained,, 

 melting at 49°-50'', from which by treatment with aniline Wallach re- 

 generated the caoutchine. From the identity of the teti-abromides, and 

 of the odours, he concluded that caoutchine and cinene (dipentene) were 

 identical. 



The isoprene, boiling-point 34°-39°, was also examined by Wallach,' 

 who confirmed the observations of Bouchardat and Tilden on the poly- 

 merisation to di-isoprene on heating, and showed by means of the tetra- 

 bromide that this also was identical with caoutchine and cinene. Wallach 

 seems to have been the first to notice the spontaneous conversion of 

 isoprene into a rubber-like product simply by the action of light. He 

 allowed isopi-ene to remain in a sealed tube in the light for a long time, 

 and on afterwards adding alcohol to the liquid a tough indiarubber-like 

 mass separated out which, on standing in the air for some time, resinified. 

 In May 1892, Professor Tilden ^ read a paper before the Philosophical 

 Society of Birmingham, in which he makes the following statement with 

 regard to the spontaneous conversion of isoprene into caoutchouc, being 

 apparently unaware of Wallach's observation : — 



' Specimens of isoprene were made from several terpenes in the course 

 of my work on those compounds, and some of them I have preserved. 

 I was surprised a few weeks ago at finding the contents of the bottles 

 containing isoprene from turpentine entirely changed in appearance. In 

 place of a limpid colourless liquid, the bottles contained several lar^e 

 masses of a solid of a yellowish colour. Upon examination this turned out 

 to be indiarubber. The change of isoprene by spontaneous polymerisation 

 has not, to my knowledge, been observed before. I can only account for it 

 by the hypothesis that a small quantity of acetic or formic acid had been 

 produced by the oxidising action of the air, and that the presence of this 

 compound had been the means of transforming the rest. The liquid was 

 acid to test paper, and yielded a small portion of unchanged isoprene. 



' The artificial rubber, like natural rubber, appears to consist of two 

 substances, one of which is more soluble in benzene or in carbon disulphide 

 than the other. A solution of artificial rubber in benzene leaves on 

 evaporation a residue which agrees in all characters with a similar pre- 

 paration from Para rubber. The artificial rubber unites with sulphur in 

 the same way as ordinary rubber, forming a tough elastic compound.' 



Bouchardat and Lafont,'' in 1886, treated caoutchine with glacial 

 acetic acid, and obtained terpineol acetate, CmHi^.CHiOj, boiling-point 

 220°, or 110°- 11.^° (10 mm.) Specific gravity, -9570' at 18° C. It" is in 

 active, and on hydrolysis with hydrochloric acid gave caoutchine dihydro- 

 chloride and acetic acid. 



By saponification of the acetate with alcoholic potash at 100° inactive 

 terpineol is formed, which, when crystallised by cooling, afterwards melts 

 at 32°. 



' A7in. der Chem,., 1887 (238), pp. 88-89. 

 ^ Chem. News, vol. Ixv., p. 265. 

 " Ann. Chem. Pltys.. 1886, pp. 507 534. 

 1906. J ■ vv ^ 



