154 



THE INDIA RUBBER WORLD 



[February i. 1904. 



vulcanizer, the conditions are such that there must be a great 

 disparity between the temperature of the vulcanizing atmosphere 

 and that of the goods to be vulcanized. An ordinary charge for 

 the dry heat vulcanizers would be perhaps 10 to 15 tons, including 

 the cars, lasts, and the boots and shoes themselves, and perhaps 

 5 to 10 tons in the steam vulcanizer, including the iron poles on 

 which the hose is made. This great mass of material must in 

 either case be brought to the temperature at which the goods 

 are vulcanized and maintained there till the operation is com- 

 plete. 



If the surrounding atmosphere be at the same temperature as 

 the contents of the vulcanizers, it is evident that the tempera- 

 ture of the contents will remain stationary. If the temperature 

 "of the atmosphere be but a little above that of the contents, it 

 is evident that the temperature of the contents will rise ex- 

 tremely slowly. In order to raise the contents within a reason- 

 able time to the temperature at which they are vulcanized, 

 whatever that may be, the indicated temperature of the sur- 

 rounding medium must at all times be considerably in excess 

 of the actual temperature of the contents. The rubber articles 

 themselves cannot be heated any faster than the iron hose 

 poles, or the wooden lasts of the boots and shoes, which are 

 very poor conductors of heat. At the beginning of the opera- 

 tion this disparity in temperature is of necessity great, but it 

 gradually grows less and less until at the end of the operation 

 it is not very large. But in no case, as such operations are 

 usually conducted, is the rubber vulcanized at the temperature 

 indicated by the thermometer, but at a considerably lower aver- 

 age temperature. It is not, however, necessary that the ther- 

 mometer should indicate the exact temperature of the rubber 

 articles. When the thermometer indicates a certain tempera- 

 ture, experience teaches how long it is necessary to subject the 

 articles to that indicated temperature, regardless of the actual 

 temperature of the articles themselves. 



In order to know the exact temperature at which rubber is 

 being vulcanized, the bulb of the thermometer must rest on the 

 rubber and be partly imbedded in it. A difference of a few 

 inches will often show a surprising difference in the tempera- 

 tures indicated by two thermometers, one of which indicates 

 the temperature of the vulcanizing chamber, and the other that 

 of the rubber itself. 



Conflicting statements of different writers as to the temper- 

 atures as to which rubber vulcanizes may be partly reconciled 

 by bearing in mind that some may have given the temperature 

 of the vulcanizing chamber, and others the exact temperature 

 of the rubber while undergoing vulcanization. In some in- 

 stances, however, such statements can be explained by neither 

 of these hypotheses, but only on the supposition that they were 

 based on reports made by persons without practical knowledge 

 of the facts. In Seeligmann's excellent work on " Indiarubber 

 and Gutta Percha," occurs the following statement : " Heinzer- 

 ling has satisfied himself by a series of direct experiments that 

 when rubber is submitted to a temperature of 100° C. (212° F.) 

 for four or five hours there is no trace of vulcanization. In or- 

 der that vulcanization may take place, it is indispensable to al- 

 ways exceed the melting point of Sulphur, that is to say 113 

 0.(235.4° F.)". It is difficult to understand the basis of the 

 latter statement, for every manufacturer of experience knows 

 perfectly-well that rubber vulcanizes below 235.4° F. Seelig- 

 mann could not have made this statement as the result of ex- 

 periments made by himself, but must have relied on reports of 

 some person who was himself ignorant of the facts. Heinzer- 

 ling's statement is not correct, though it may be based on a 

 slight foundation. A compound consisting of 12 pounds well 

 dried fine Pari rubber, 6 pounds litharge, 6 pounds whiting, 



and 6 ounces of Sulphur, a very common compound, vulcanizes 

 rapidly in ten hours by the dry heat process at 212° F., and 

 shows signs of vulcanization when it has been submitted to 

 that temperature for four or five hours. But, if the same com- 

 pound be submitted to the same temperature surrounded by 

 metal and the air be carefully excluded it vulcanizes well in four 

 and one half to five hours. Signs of vulcanization will be ob- 

 served after about two and one half to three hours. If, how- 

 ever, the percentage of Sulphur in the compound be increased 

 from 3 per cent, to 7% per cent., thorough vulcanization will 

 take place at 212" by the dry heat process in five hours. If the 

 air of the vulcanizing chamber be impregnated with Sulphur, 

 by sprinkling a little of it on the floor, then the compound 

 containing 3 per cent, of Sulphur vulcanizes readily at 212° F., 

 in three hours, and that containing yyi per cent, in two and a 

 quarter hours. The latter compound will be fairly vulcanized 

 in about an hour and a quarter. Heinzerling therefore could 

 not have been very thorough in his experiments. Any person 

 wishing to test these statements should use an accurate chem- 

 ical thermometer and be careful to keep the bulb partly im- 

 bedded in the rubber so that the exact temperature of the 

 rubber will be indicated. No theory can be considered estab- 

 lished from the result of one or two experiments. In order 

 to establish any theory a large number of experiments under 

 varying conditions are absolutely necessary. 



In considering the subject of vulcanization, the very founda- 

 tion of any investigation should be the temperatures at which 

 the rubber vulcanizes. Any error in this respect is inexcus- 

 able, as all theories based on such an error lose whatever force 

 they might otherwise have. Rubber not only vulcanizes read- 

 ily at 212" F., but at much lower temperatures provided the 

 proper proportionate time be allowed, and also provided that a 

 reasonable compound be employed. The compounds given 

 above vulcanize readily both at high and at low temperatures, 

 as proved by a large number of direct experiments made at 

 every 10 degrees between 172 and 445° F. The result of these 

 experiments and the general rule applying to chemical combi- 

 nations, warrants the assertion that vulcanization can proceed 

 at temperatures down to and possibly below the ordinary tem- 

 peratures, if sufficient time be allowed and if the compound be 

 adapted to the temperature. Furthermore, rubber vulcanized 

 at the low temperatures mentioned is fully as strong and elas- 

 tic as rubber vulcanized at high temperatures. It resists the 

 action of heat and cold and the usual solvents of rubber in every 

 respect the same as if it were vulcanized at high temperatures. 

 No difference can be discerned in any of its physical or chemical 

 properties. Hence, whatever be the temperature at which rubber 

 may be vulcanized the result of vulcanization must be the same 

 so far as the result of the reaction is concerned. " Different 

 bodies which consist of the same substance agree not only 

 approximately, but exactly in their properties. Hence, bodies 

 that agree exactly in their properties consist of the same sub- 

 stance. This law is the fundamental law of chemistry." 



The governor of the Straits Settlements — Sir Frank A. 

 Swettenham — in an address before a recent convention of na- 

 tive sultans and datos at Kwala Lampur, in Selangor, said, on 

 the subject of planting : " The prospects of rubber are so good 

 that unless some unforeseen disaster happens the future is full 

 of promise for those who have taken up this cultivation. The 

 area at present under rubber (principally the Para variety) is 

 given approximately at 16.000 acres." These figures relate to 

 the Straits Settlements proper and the adjacent Federated Ma- 

 lay States. Sir Frank, by the way, after a long service in the 

 Far East, has retired. 



