468 The Supplement to the 



RUBBER ANB GUTTA PERCHA ANB 

 "THE TERPENES." 



"A CHAPTER IN MODERN SYNTHETIC 

 CHEMISTRY." 



Sir William A. Tilden is, if we are not mis- 

 taken, about the oldest Chemist in England 

 and the gentleman who, a few years ago when 

 the British Association met at York, was good 

 enough to forward a message to the RubberPlan- 

 ters of Ceylon. Theoccasion and the message re- 

 quire explanation. In the Chemical Section 

 of the Association, a paper on Synthetic Rubber 

 was read and discussed at length, chiefly by 

 young Chemists who seemed to be sanguine of 

 being able very soon to turn out a good artificial 

 rubber and prove it a commercial success. There 

 was one senior member of keen intellectual fea- 

 tures, grave and silent during the discussion, and, 

 enquiring about his personality, we were told 

 that was " Tilden," the oldest if not the ablest 

 Chemist in England. Plucking up courage, we 

 ventured, as the sitting ended, to make an 

 introduction, how we were from Ceylon and to 

 many of its planters we were afraid the views 

 just expressed of an expectation of a cheap 

 useful synthetic rubber, would spell great loss 

 if not ruin, would hekindly say if he agreed with 

 the sanguine opinions of his younger brethren. 

 The purport of the answer (and message) of 

 Mr. (now Sir W. A.) Tilden (given to Mr. J. 

 Ferguson) can be indicated in this way :— Tell 

 your friends in Ceylon that if I were a young 

 man and a planter in your island that I would 

 not hesitate to plant as many Rubber trees 

 as I could manage without troubling myself 

 about the laboratory experiments of the gentle- 

 men who have spoken towards a synthetic 

 rubber. That such a rubber might be managed 

 to a useful degree, was quite possible in time ; 

 but whether the result could ever compete 

 with the natural product in quality or prices 

 was a different matter altogether. Evidently, 

 some years ago— and no doubt still— Mr. now 

 Sir William A. Tilden was not sanguine at all 

 on the point. This little bit of experience at 

 York in August, 1906, makes anything that falls 

 from the pen of the veteran Chemist of much 

 interest and in Murray's "Science Progress" 

 we have a paper of his entitled " The 

 Chemical History of the Terpenes," in 

 which we find a few passages which bear on 

 " synthetic rubber." First of all, Sir William 

 opens his article as follows : — 



The hydrocarbons known as the terpenes 

 have long attracted the attention of chemists, 

 on account of their wide diffusion in the vege- 

 table kingdom and their frequent association 

 with the odorous principles of plants, though it 

 is only during the last thirty to forty years that 

 systematic research has been rewarded with 

 such a measure of success that it can be said 

 that the properties and chemical constitution 

 of all the more important members of the group 

 are now as well understood as those of any 

 group of carbon compounds. 



The terpenes are highly interesting from two 

 distinct points of view. As already mentioned 

 they are important for commercial reasons not 



Tropical Agriculturist 



only on account of the use of some of them 

 as solvents, especially the oils of turpentine in 

 varnishes and paints, but they are characteristic 

 and often predominant constituents of many 

 essential oils used in medicine and perfumery. 

 They have also been made the starting-point for 

 the manufacture of certain substances — cam- 

 phor and terpineol, for example, which are 

 extensively used for such purposes. 



But the history of the investigations by which 

 the chemical constitution of many of the ter- 

 penes has at last been elucidated is specially 

 interesting to the scientific chemist on account 

 of the nature of the problems to be solved, the 

 poculiar elusive transformations of the hydro- 

 carbons and their derivatives and the ultimate 

 success of these investigations, which provides 

 a triumphant vindication of the principles 

 which underlie modern synthetical chemistry. 

 These principles concern not only the student 

 of " organic " chemistry, for they are necessarily 

 involved in general conceptions regarding the 

 constitution of matter. 



And after some fourteen pages mainly tilled 

 with technical details, we come upon the 

 following: — 



Isoprene heated alone in a sealed tube is con- 

 verted into dipentene mixed with viscous pro- 

 ducts of its polymerisation. Bat if it is kept for 

 some months or years under conditions which, 

 except exclusion of air, have not been exactly 

 determined, it passes spontaneously into a 

 syrupy liquid which gradually deposits solid 

 masses of rubber. Rubber is also formed when 

 isoprene is heated with small quantities of acetic 

 and other acids. This observation, made more 

 than twenty years ago, has led to various at- 

 tempts to employ isoprene as a practical source 

 of rubber on a manufacturing scale. 



When rubber or gutta-percha is destructively 

 distilled it yields a mixture of hydrocarbons from 

 which can be separated as chief products, isop- 

 rene and dipentene, originally called, caoutchine. 

 It would appear from this that rubber is a com- 

 pound, the formula of which is either (CioHi6) n 

 or(C5H8)n. From the direct conversion of 

 isoprene into rubber the latter formula seems 

 the more probable, especially as the temperature 

 at which rubber decomposes is much below that 

 at which depentene is broken down under the 

 influence of heat. Indeed, it seems not impro- 

 bable that the dipentene which accompanies 

 isoprene in the distillation of rubber is a secon- 

 dary result of the polymerisation of isoprene by 

 heat. The condensation of isoprene into dipen- 

 tene is easily represented as in the following for- 

 mula where two molecules of isoperne are united 

 by the dotted lines, the valencies adjusting 

 themselves but without further change : * * * 



To represent the condensation of isoprene into 

 caoutchouc, Harries assumes the formation of 

 an octadiene as the first product of the union of 

 two molecules of isoprene, rubber consisting of 

 multiples of this or (CioHi6)n. * * * 



Caoutchouc is a colloid of very high molecular 

 weight and if it is assumed to be made up of a 

 number of such groups united together, it is 

 difficult to explain why rubber should break 



