NA TURE 



3*3 



THURSDAY, FEBRUARY 5, 1903. 



INDIA-RUBBER. 

 The Chemistry of India-rubber. By Carl Otto Weber, 

 Ph.D. Pp. x + 314. (London : Chas. Griffin and 

 Co., Ltd.). Price 16s. net. 

 INURING the last few years the development of the 

 *-J india-rubber industry to meet cycling, motoring, 

 and electrical requirements has produced quite a crop of 

 descriptive handbooks, among which those of Brannt, 

 Henriques, Seeligmann, Clouth and Warburg are the 

 works which come most readily to mind. As a rule, 

 however, these treatises have dealt more particularly 

 with the manufacturing and commercial aspects of india- 

 rubber production, and the scientific side of the subject 

 occupies in them a relatively subordinate place as one 

 matter among many. In the volume before us, the 

 author has applied himself specifically to the chemistry 

 of india-rubber, and incidentally to that of its various 

 substitutes. Dealing, as he does, with only the scientific 

 portion of the subject, he has naturally treated this 

 branch far more exhaustively than previous writers have 

 done. But pure science is even here tempered to the tech- 

 nologist, for almost throughout the book the point of view 

 is that of the working — one had almost said of the 

 works — chemist. Theoretical exposition and practical 

 application jostle one another in every chapter ; what to 

 do, and the reason for doing it, rub shoulders together 

 from cover to cover. It may be said at once that the 

 result is an eminently useful contribution to the literature 

 of india-rubber and its congeners. 



The book contains nine chapters and an appendix. 

 In the first chapter, which forms more than a third of the 

 work and gives its title to the whole, Dr. Weber deals 

 with the constituents of india-rubber, discusses their 

 physical and chemical properties, and propounds in 

 outline a theory of vulcanisation. The carbohydrates 

 present in crude "unwashed" rubber are first referred 

 to, and then follows a useful little table showing the pro- 

 portions of resinous extract obtained from the various 

 commercial brands of technically-pure rubber by treat- 

 ment with acetone. It may be explained that the import- 

 ance of these " resins " lies in the fact that they allow 

 the chemist to discriminate between a high-quality 

 rubber, such as Par£, and an inferior product like some 

 of the African kinds. 



Passing on to india-rubber proper, the author sum- 

 marises the evidence which goes to prove that the pure 

 rubber substance is a hydrocarbon of the terpene type. 

 Oxygen, it is true, is always present in commercial 

 specimens, but it is partly accounted for by atmospheric 

 oxidation and partly by the presence of an "insoluble" 

 compound having the empirical formula of a hydrated 

 terpene. This last, the author suggests, may be an 

 intermediate product between india-rubber itself and the 

 carbohydrates from which, perhaps, the various terpenes 

 are manufactured in the cells of the rubber plant. 



Organic chemists have apparently found the chemistry 



of india-rubber somewhat unattractive. Gladstone and 



Hibbert's well-known paper, published some fifteen years 



ago, still remains the chief contribution to the subject. 



NO. 1736, VOL. 67] 



No doubt this is largely due to the intractable nature of 

 the compound ; for india-rubber, from this point of view, 

 certainly possesses the defects of its qualities. It has 

 few points of attack ; there are none of the carbonyl-, 

 carboxyl-, amido-, imido-, hydroxy- or methoxy-groups 

 in which the organic manipulator delights ; it cannot be 

 readily dissolved ; and a fortiori, being a colloid, it cannot 

 be crystallised. Nevertheless, it has one vulnerable spot, 

 and the Achilles' heel in this case is found in the exist- 

 ence of the "ethylene bonds" pointed out by Gladstone 

 and Hibbert in the paper already referred to. The 

 advances that have been made in the chemistry of this 

 refractory substance have followed almost exclusively 

 from the study of india-rubber as an " unsaturated " 

 compound. From a consideration of its addition- 

 products, our author concludes that the india-rubber 

 molecule has probably an open-chain structure, and that 

 its molecular weight corresponds, in all likelihood, to a 

 high multiple of the empirical formula C 10 H 16) with 

 C 5U H S1) or C C0 H 9(i as a possible minimum. 



Much stress is laid upon the colloidal properties of 

 rubber as being the clue to a proper understanding of its 

 behaviour during manufacture. Graham's classical re- 

 searches on colloids we are all supposed to know, at least 

 in substance ; but Dr. Weber appears to think — perhaps 

 justly — that most of us are content to take them as read, 

 since he remarks that they are, if not forgotten, certainly 

 realised by very few present-day workers. For our sins 

 in this respect we are treated to a twenty-five page 

 disquisition on the colloidal state, leading up, however, 

 to an interesting study of the phenomena of vulcanisation. 



In the author's view — the experimental evidence for 

 which is set out at some length — the vulcanisation of 

 india-rubber by means of sulphur consists essentially in 

 the direct addition of sulphur to the india-rubber hydro- 

 carbon (polyprene), with the formation of various polyprene 

 sulphides ranging between the limits C 100 H 1CO S and 

 C„, H li;0 S 2l) . The particular sulphide produced de- 

 pends upon the degree of vulcanisation, which itself 

 is a function of the temperature, time, and proportion 

 of sulphur present. Combating the theory that the action 

 of the sulphur is one of substitution instead of addi- 

 tion, the author rightly points out that if the former were 

 the case the vulcanisation of a ton of rubber would mean 

 the production of about 18,000 litres of hydrogen sul- 

 phide — a daily amount which would make the vulcan- 

 ising rooms fairly reek with the gas. In reality, only 

 insignificant traces are found there. The cold process 

 of vulcanising by means of sulphur chloride is also 

 discussed in detail ; alternative methods are mentioned, 

 and the whole section, which is embellished by half-a- 

 dozen photo-micrographs, forms a highly interesting 

 and suggestive little monograph upon the inter-relations 

 of sulphur and rubber. 



In the succeeding chapter the technical examination 

 and valuation of india-rubber and gutta-percha are dealt 

 with. But in this industry, as in so many others, our 

 manufacturers cling hard to rule-of-thumb methods ; 

 stocks are bought on the strength of a cursory empirical 

 examination ; and we read that, in consequence, different 

 lots, supposed to be of identical quality, "often show the 

 most absurd variations " when properly appraised by 

 analysis. The following quotation speaks for itself: — 



P 



