March i, 1904.] 



THE INDIA RUBBER WORLD 



187 



THE ART OF VULCANIZATION.* 



IT is only recently that it has become understood that in 

 vulcanization there is a chemical union of rubber and sul- 

 phur. In fact, it is so recently, that manufacturers gener- 

 ally cannot be said to have had their attention called to 

 it, until within the past few months. The first authoritative 

 announcement of the fact in a manner to command the atten- 

 tion of manufacturers in the United States was the publication 

 in England early in 1903 of Dr. Weber's most excellent work on 

 the " The Chemistry of India-Rubber." But the circulation of 

 such a work in this country is necessarily slow, notwithstand- 

 ing that it is a work of such a character that it should not only 

 be read, but carefully studied by every manufacturer. 



Very shortly after the publication of Dr. Weber's work there 

 was published, also in London, a translation of another excel- 

 lent work, published in France, by T. Seeligmann, a French 

 chemist, and others, entitled " Indiarubber and Gutta Percha." 

 Even at the date of this publication, Seeligmann did not agree 

 with Dr. Weber to the proposition that in vulcanization there 

 is a chemical union of rubber and sulphur, but thought that 

 perhaps the mixture of rubber and sulphur was in the nature of 

 an alloy. Quoting in his work the opinions of Payen, Heinzer- 

 ling, Unger.and Donath on the subject, Seeligmann summarizes 

 their views as follows : 



These authors therefore consider vulcanized rubber as a sort of alloy 

 of the organic substance of the rubber with the sulphur or with a sulphide 

 or even with the chloride, bromide or iodide of sulphur. This condition 

 is not combination properly so called, from which the formation of a well 

 defined chemical individuality would result. It differs, however, from 

 a simple solution or mechanical mixture. 



Seeligmann's own opinion is given as follows : 



From this point (248° V.) the sulphur modifies its condition ; it melts, 

 at the same time that the pores of the rubber are sufficiently dilated to 

 allow of the gradual absorption of the liquid vulcanizer — sulphur. But 

 at the same time as the chemical action commences, the liquid sulphur 

 combines with the adhesive hydro carbide, and forms with it a new 

 chemical body or rather an alloy. This action naturally continues if the 

 process be prolonged at the same temperature, so that it penetrates 

 further and further into the mass. 



Aside from Dr. Weber's work we do not remember any pub- 

 lic announcement in this country of the result of recent analy- 

 ses which showed conclusively the chemical nature of the reac- 

 tion until The India Rubber World referred to it in a recent 

 issue. 



Thus the knowledge of the true nature of the chemical reac- 

 tion in the vulcanizing process cannot be said to have become 

 known to manufacturers generally until a very recent period. 

 Prior to that they had been engaged for upwards of half a cen- 

 tury in developing and extending the manufacture of vulcan 

 ized rubber goods in ignorance of the true nature of the pro- 

 cess. They developed the business from an insignificant amount 

 in 1844 until it has become one of the leading industries of our 

 land. The application of vulcanized rubber has been contin- 

 ually extended until it can be safely said that to-day there is 

 not an art or a science that is not more or less dependent upon 

 its use. But it is only the physical characteristics of vulcanized 

 rubber that at present concerns the manufacturers or the pub- 

 lic as it has during the past fifty years. While this is so, the 

 chemical nature of the problem should in nowise be overlooked. 

 Now that the true nature of the reaction is understood we may 



* Copyright, 1904, by The India Rubber World. 



confidently look forward to discoveries in the near future that 

 will be of inestimable benefit to the manufacturer. 



It is popularly believed that the art of vulcanization consists 

 in submitting crude rubber to the action of heat in connection 

 with sulphur, whereby the characteristics of the rubber are so 

 changed as to produce an article which is strong, durable, and 

 which possesses all the qualities usually associated with vulcan- 

 ized rubber. This however is an error, as crude rubber is sel- 

 dom, if ever, submitted to the vulcanizing process. No use can 

 be conceived for crude rubber that might be vulcanized by any 

 process. It is only rubber that has been through the various 

 processes of washing, drying, masticating, compounding, and 

 calendering that is ever submitted to vulcanization. In each of 

 these operations its properties are changed in some respect. 

 By the time that rubber compounds are ready for shaping into 

 the various articles for which they are intended, the crude rub- 

 ber has lost nearly all of its distinguishing physical character- 

 istics. It is the province of the curing, the final step of the 

 vulcanizing process, to restore to these compounds the original 

 qualities of crude rubber, and to add the properties of resisting 

 the action of heat, cold and its ordinary solvents. Aside from 

 these latter no new physical qualities whatever are the result 

 of vulcanization. 



The art of vulcanization includes every step in the process 

 from the crude rubber to the finished product. In each of 

 these steps, the extent of the change which takes place in the 

 properties of the rubber depends entirely on the judgment of 

 the operator. In each step before the final one, the workman 

 handles the stock and is thus enabled to judge when his part 

 of the operation has been properly performed. The final re- 

 sult, however, is materially affected by any error in judgment 

 on the part of any operator. In order to ensure a successful 

 result of the vulcanizing operation each step of the process 

 must be performed with a due regard for the operations which 

 have preceded or which may follow. 



The submission of rubber to the action of heat at a vulcan- 

 izing temperature does not of itself result in vulcanized rubber. 

 Something more is necessary. This part of the process, like 

 each other part, must be conducted with reference to the pre- 

 ceding operations, for the result is absolutely controlled by the 

 manner in which those operations have been performed. To 

 this end, the workman proceeds in accordance with a formula 

 given him which is adapted to the particular class of goods to 

 be vulcanized. No matter how skilful the workman may be, 

 be cannot in applying the formula control the result. As the 

 operation progresses he does not handle the goods, he does not 

 see them, and, in all operations under pressure, he cannot see 

 them until the operation is completed. There is thus no op- 

 portunity or need of exercising any discretion. But even here 

 a large experience is necessary. For often it is not possible to 

 follow the formula exactly. Sometimes the temperature rises 

 too fast, sometimes too slowly. He must then be able to judge 

 how much more time or how much less, will fulfil the require- 

 ments of the formula. But this is not a discretion that con- 

 trols the result. 



The art of vulcanization cannot be learned from books — only 

 from experience. This, however, does not imply that informa- 

 tion obtained from books is of no value. On the contrary, the 

 information given in books by investigators of ability and 

 thorough acquaintance with the art, must be exceedingly valu- 



