6 SCIENCE PROGRESS 



appears in 1872 in the Chemical News, where Donkin advocates 

 dipping the knife or cork-borer in solution of caustic potash 

 when desiring to cut or bore indiarubber corks. 



Natural rubber is obtained from the latex by a process of 

 coalisation apparently depending on the coagulation of the 

 protein, or other protective colloid. The coagulation is brought 

 about by heat, by the addition of acids, generally acetic, and 

 by other methods. The globules of rubber rise through the 

 liquid, coalesce and yield a tough elastic mass, which may be 

 regarded as an emulsoid gel. Raw rubber contains as its 

 principal constituent a hydrocarbon of the composition Ci Hi 6 , 

 the amount of which may reach as much as 95 per cent. Much 

 early work was done on the destructive distillation of rubber 

 from the time of Dalton. Its empirical constitution was deter- 

 mined from analyses made by Faraday, Berzelius, Ure and 

 others. The first important chemical research on this subject 

 was made by Greville Williams in i860. He distilled rubber 

 in an iron vessel at a low temperature, and obtained isoprene, 

 C 5 H 8 , and cautchine, Ci Hi 6 , which latter substance Wallach 

 subsequently showed to be identical with dipentine. Greville 

 Williams also noticed the transformation of isoprene into a 

 rubber-like body, of which the quantity was insufficient for 

 identification, but he evidently considered caoutchouc to be 

 a polymer of isoprene. In 1875 Bouchardat investigated the 

 products of the distillation of rubber, and came to the con- 

 clusion that the substances he obtained, Ci Hi 6 , C 15 H 2 4, etc., 

 including rubber itself, are polymers of isoprene. In 1879, 

 while preparing the hydrochloride of isoprene, by shaking with 

 concentrated hydrochloric acid, a rise of temperature indicated 

 that combination had occurred, but on distillation a solid 

 residue remained which was found to have " the elasticity and 

 other properties of rubber itself." 



In 1882 Tilden showed that the colourless syrupy substance 

 resulting from the atmospheric oxidation of isoprene is con- 

 verted into true rubber when brought into contact with 

 strong aqueous hydrochloric acid, or nitrosyl chloride, remark- 

 ing that "It is this character of isoprene which gives it a 

 somewhat practical interest, for, if it were possible to obtain 

 this hydrocarbon from some other and more accessible source, 

 the synthetic production of rubber could be accomplished." 

 At the same time Tilden proposed the constitutional formula 



