The Nature of Vulcanization. Part IV (Continued)

In a previous communication the authors have discussed the limiting figure for combined sulfur in vulcanized rubber, and shown that under suitable circumstances the coefficient of vulcanization can exceed the figure of 47, which is that required by the formula C5H3S. It was thought that the combined sulfur in excess of this amount resulted from the substitution of sulfur for hydrogen. (Further information on this point will be found in the second part of this paper.) In the course of these experiments use was made of the ether-hydrochloric acid extraction method for the removal of mineral sulfides in soft vulcanized rubber. It was thought that this extraction method might not be suitable for use with vulcanites, since the amount of swelling produced by the ether was relatively inappreciable, and consequently the metallic sulfides were not necessarily decomposed. It was also thought that the acid mixture might react with a part of the rubber sulfide and result in a lower coefficient, which would depend on the time of extraction. It is known that vulcanite can be decomposed by the action of alcoholic potash, and the combined sulfur has been reduced in some cases to 26 per cent. It is reasonable to suppose that decomposition takes place in the presence of concentrated hydrochloric acid. In order to determine the extent to which the sulfide is decomposed by the action of the acid a series of extractions was made.