212 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1940 



Since we are today celebrating the centenary of the great invention 

 of vulcanization, let us note that this principle, with some modifica- 

 tions, applies to these newest achievements of the chemists, although 

 as far as we know, Goodyear himself never foresaw the possibility 

 of vulcanizing any material other than rubber. 



NoNBUTADiENoiD SYNTHETICS : Several products in this group are in 

 commercial use. Although these materials do not have a close resem- 

 blance chemically to rubber, their physical properties permit them to 

 ba handled on rubber machinery. The principal products in this 

 group are : 



Polyvinyl compounds. — Plasticized polyvinyl cliloride, known as 

 Koroseal, is used for products where resistance to corrosive chemicals 

 is important. Plasticized polyvinyl alcohol is employed for certain 

 applications where high resistance to oils and other solvents is required. 



Reaction products of ethylene dichloride and similar compounds 

 with sodium polysulfide, known as Thiokol, are rubberlike bodies 

 characterized by good resistance to oil. 



Polyisobutene, known as Vistanex, is a rubbery polymer which is 

 used in electrical and other applications. 



It is not possible at this time to make any prediction as to the 

 extent to which these or any other synthetic materials will replace 

 natural rubber. Synthetics cost more than rubber and, although 

 they are superior to rubber in some respects, they are inferior in 

 others. Assuming that the supply of natural rubber is not interfered 

 with by war or any other circumstance, the question as to whether 

 or not any substantial amount will be replaced by synthetic mate- 

 rials depends on the price at which synthetics can be made, and on 

 how good the product is, both from the standpoint of ease of proc- 

 essing and the quality of the finished article. 



It is quite likely, however, that as new fields for rubberlike prod- 

 ucts are developed, the synthetic materials will be used in increasing 

 amounts, since they are suited to applications for which natural 

 rubber is unsuited. 



THE MODERN TIRE 



The modern automobile tire is a concrete example of most of the 

 important teclmological advances which we have been discussing. 

 Those of us who can recall the goggles and linen duster era of the 

 motor car will also undoubtedly have vivid recollections of the trou- 

 bles of the motorist of that day. On long trips it was customary to 

 carry several spare tires on account of frequent blowouts and punc- 

 tures. It is now customary in most cases to carry only one spare 

 tire, and that is seldom used. In addition to these difficulties the 

 tires wore out so rapidly that tire cost was one of the important items 

 of expense in car operation. During the first decade of the twentieth 



