102 GOODYEAR ON GUM -ELASTIC. 



heat to it from design, or for the purpose of divesting it of the 

 objectionable quaUty, adhesiveness, when it was so well known 

 that it would melt at a low temperature. It is the use of a high 

 degree of heat, an agent so destructive to the native gum, which 

 forms the broad distinctive feature which characterizes this pro- 

 cess. And to this time it appears to be utterly impracticable to 

 apply this high degree of heat to the gum, except in combination 

 with sulphur, in some form or other. There have been, however, 

 many modifications of the process, and attempts at evasions of 

 the patents, by combining with them other substances that are 

 wholly inert, and not necessary to produce the best result. 



Among many experiments for drying and curing the gum, 

 (supposing the only difficulty with it to be too great adhesive- 

 ness,) the inventor was much elated with the result of one, 

 which was then every way satisfactory. By this experiment, 

 from one half to a pound of magnesia was mixed with the 

 pound of gum. This compound had the great advantage of 

 being white, which was very desirable for many purposes, as no 

 India rubber goods except black had before that time been 

 made in the United States, and no India rubber fabrics in 

 Europe, but those of the Macintosh manufacture, in which the 

 gum is put between two cloths. He then supposed that mag- 

 nesia, in combination with gum, had the effect to dry it, which 

 some other substances have to dry paints. 



A book was bound with this compound, (made without sul- 

 phur,) in 1834, the cover of which softened and fermented at 

 that time, but is now hard as shell. It is known to chemists 

 that magnesia and turpentine make a hard substance, and this 

 appears to be only a chemical result of the same character. 



A compound is now made by the metallizing or vulcanizing 

 process, with calcined magnesia combined with the gum, which 

 has a peculiar hardness and solidity, and which it is thought 

 makes it better adapted to some particular uses than the ordi- 

 nary compound of vulcanized gum-elastic ; and it has not yet 

 been found to change or become too hard by age, like the 

 article above described. 



