240 KEPORTS ON THE STATE OF SCIENCE. 



considered it identical with terpiline, the optically inactive hydrocarbon 

 of turpentine oil, the dihydrochloride being identical with terpiline hydro- 

 chloride. He also suggested the identity of this di-isoprene with caout- 

 chine and with the hydrocarbon from terebinthine, as he was able to 

 obtain terpine hydrate from all three. 



Subsequently Bouchardat investigated the action of hydrogen chloride 

 and hydrogen bromide on isoprene itself, and found that here also, two 

 hydrochlorides and hydrobromides were produced by the addition of one, 

 or two, molecules of the halogen acid. The following compounds were 

 prepared : — 



Boiling-point. Specific Gravity. 



aH^HCl. . . 85°-9l° 0-868 at 15° 



aH,2HCl . . 145°-953° 1 065 at, 16° 



aH.HBr. . . 10i°-108° 1-173 at 15° 



C^HsBr^ . . . 176°-180° 1-601 at 15° 



as were also several other halogen compounds and their derivatives. 



A very interesting observation was also made by Bouchardat, viz., 

 that on treating isoprene with cold aqueous hydrochloric acid, saturated 

 at 0° C, an elastic polymer was obtained, which after boiling with water 

 possessed the properties of indiarubber. It had the same percentage com- 

 position as isoprene, was insoluble in alcohol, swelled upon treatment 

 with ether, and dissolved in carbon disulphide like indiarubber. On dry 

 distillation the same hydrocarbons are produced as in the case of caout- 

 chouc. One of these, CmHi^, was isolated, and was identical with a similar 

 hydrocarbon obtained from caoutchouc, yielding on treatment with hydro- 

 gen chloride a solid hydrochloride melting at 46°. 



If this substance obtained by Bouchardat was really indiarubber, this 

 work constitutes the first partial synthesis of this hydrocarbon. The 

 isoprene used was, however, itself obtained from rubber. This same 

 elastic polymer was subsequently obtained by Professor W. A. Tilden/ 

 in 1882, with isoprene from other sources. By passing turpentine oil 

 through a red-hot tube and fractioning the products of decomposition, 

 Professor Tilden isolated a small quantity of a liquid, boiling-point 37° the 

 vapour density of which corresponded with the formula C^Hg, and which 

 was apparently identical with isoprene. On treating this with concen- 

 trated hydrochloric acid he obtained a tough elastic product closely re- 

 sembling caoutchouc. Isoprene from rubber was al&o examined by Tilden, 

 who confirmed Bouchardat's observations, except that he found the boiling- 

 point to be 35°. He also obtained the elastic polymer by treatment 

 with nitrosyl chloride, and prepared isoprene tetrabromide C5HsBr4 for 

 the first time. In his publication Tilden also discussed the question of 

 the constitution of isoprene, and concluded tiiat isoprene is /3 methyl 

 crotonylene 



CH3X 



>C-CH = CH, 



ch/ 



a view which has since received synthetical confirmation. 



Dr. O. Wallach,'- in 1885, conducted a thorough investigation of the 

 hydrocarbons, caoutchine and isoprene, obtained by the distillation of 



' Chem News, 1882, pp. 120-121 ; Brit. Assoc. Report, Southampton, 1882. 

 • Ann. 'der Chem., 1885 (227). pp. 292-296; 1884 (225), p. 311. 



