ON THE PRESENT POSITION OF THE CHEMlSTllY OF KUBBEK. 239 



properties, decolouring indigo sulphate and converting lead sulphide into 

 lead sulphate. By careful distillation of this sticky product some isoprene 

 first passed over ; the temperature then rose quickly, and the residue was 

 converted into a white spongy mass, which consisted of carbon, hydrogen, 

 and oxygen. Analysis gave : — 



C = 78-7 H = lO-7 = 10-5 



Calculated for C,„H,^0 

 C = 78-94 U = 10 52 O =10-51 



Isoprene also readily combined with bromine, the action being some 

 what violent. 



Caoutchine. 



Fraction No. 2. The portion boiling at 1 70°-180° was further rectified, 

 and Williams obtained a fraction boiling almost constantly at 170°-173°, 

 which was identical with the caoutchine obtained by Himly (boiling at 

 171°). 



Gutta-percha also yielded the same fraction, and the mean of the 

 analyses of samples from both sources gave : — 



C = 88-l H = ll-9 



Himly's figures . C = 88-4 H = 11-5(5 



Greville Williams showed that the vapour density of caoutchine was 

 double that of isoprene, and observed that it belonged to a group of substances 

 isomeric with turpentine- oil, the same quantity of bromine being absorbed 

 by it|,'as|"^by turpentine-oil. He described the preparation of the 

 bromide,' and on distillation of this brom compound with potassium he 

 obtained an oil boiling at 170°- 200°, which he considered to be cymene. 

 On oxidation with sulphuric acid and potassium dichromate, this oil 

 gave an acid apparently identical with the isolinic acid obtained by 

 Hofmann. An oil boiling at 300° was also produced, which Williams 

 termed paracymol. 



On treating caoutchine with an excess of concentrated sulphuric acid 

 there resulted a thick liquid from which, on treatment with lime, Williams 

 obtained a calcium salt of the empirical formula C2oHi5CaS.20g. 



Isoprene, thus obtained by Williams, was afterwards the subject of 

 further investigations by M. G. Bouchardat.^ On heating isoprene in a 

 sealed tube containing carbon dioxide for ten hours at 2y0°-290° Bou- 

 chardat obtained a viscous sticky mass which no longer boiled at 38°. 



On distillation this gave (1) some unchanged isoprene ; (2) an inactive 

 hydrocarbon boiling at 170°-185°, having an odour like lemons, specific 

 gravity "866 at 0°, and composition CioH,g; (3) other higher boiling con- 

 densation products. 



The hydrocarbon boiling at 170°-185° was optically inactive and 

 absorbed oxygen from the air. Bouchardat found that it combined with 

 hydrogen chloride in ethereal solution, giving two different compounds — 

 (1) a hydrochloride boiling at 145° (100 mm.), having the composition 

 CmHigHCl; and (2) a solid dihydrochloride melting at 49°-5, having 

 the formula CioH,62HCl. 



The name of di-isoprene was given to this hydrocarbon, a polymer of 

 isoprene, the boiling-point of which was found to be 174°-6. Bouchardat 



' Cowj^^es ^e«<Z«s, Ixxxix. p. 1117 (1879). 



