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132 GOODYEAR ON GUM-ELASTIC. 



eral comparisons or illustrations in this place may serve to give 

 some persons a more correct idea of the nature of the results 

 produced by the discovery of the process of vulcanizing, or 

 heating, as it was first called by the inventor. 



The change wrought in the native gum by this process may 

 with propriety be compared to that which is wrought in a per- 

 ishable skin or hide, by the process of tanning, which converts 

 it into a beautiful kid, or substantial leather ; or to that by which 

 the crude ore is changed, by the process of smelting, into valua- 

 ble iron for man's use ; or to that by which iron is changed by 

 the well known process of baking with carbon, into steel. This 

 latter comparison holds good, not only as to the results, but also 

 as to the method, except that instead of carbon, sulphur is used 

 in the baking process, treated of for vulcanizing the gum, 

 which is penetrated by sulphur after it has taken the form of a 

 gas, a high degree of heat being used in both cases. One 

 remarkable fact is exhibited by this improvement, which is an 

 apparent anomaly in chemistry. An article is obtained which 

 is not dissolved without great difficulty, by the best known sol- 

 vents of gum-elastic, which yet possesses all the valuable proper- 

 ties of the native gum, and many others that the native gum 

 does not possess. It will be readily perceived, that the effect 

 of this process is not simply the improvement of a substance ; 

 but it amounts, in fact, to the production of a netv material. The 

 durability imparted to gum-elastic by the heatmg or vulcan- 

 izing process, not only improves it for its own peculiar and 

 legitimate uses, but also renders it a fit substitute for a variety 

 of other substances where its use had not before been contem- 

 plated. It may, at first thought, appear absurd to compare 

 the durability of an article like gum-elastic, with that of metal 

 or wood, yet it will be found upon investigation, that in con- 

 sequence of its resistance of corrosion and decay, it is, for 

 certain purposes, far more durable than either of these, as has 

 been found by actual trial. Nitric acid quickly destroys iron, 

 brass, copper, &c. Potash destroys leather, and wood. Some 

 fabrics are rendered unfit for use, by coming in contact with 



