92 PLANT COMPOUNDS 



to the air. It is soluble in chloroform, benzine, and toluene, 

 and is rendered hard and brittle after a time by oils. Chlorine, 

 bromine, and strong acids destroy it. The commercial 

 material is practically black from smoke and dirt, containing 

 in addition to the rubber proper, or the hydrocarbon, some 

 fat, waxes, and proteins, which were originally in the latex. 

 In addition there are chips, bark, and dirt of various kinds 

 accidentally present or intentionally added. 



The crude material is ground and washed, and for use 

 must be treated with sulphur, metallic sulphides, or metallic 

 oxides. The pure rubber is very sticky, but on heating with 

 5 to 10 per cent, of sulphur it loses its stickiness, becomes 

 more elastic, and is the usual form of soft rubber from 

 which so many articles are manufactured. When heated 

 with antimony pentasulphide it forms "red" or "antimony" 

 rubber. Red antimony trisulphide is formed, the rest of the 

 sulphur uniting with the rubber. If the pure rubber is 

 heated with 25 to 30 per cent, of sulphur, it forms on cooling 

 a hard, hornlike mass, called ebonite, or hard rubber, which 

 finds a great variety of uses too well known to need mention. 

 The sulphur may form a chemical compound with the 

 hydrocarbon or it may be merely a physical mixture of 

 sulphur and hydrocarbon. 



(b) Gutta Percha. — This material is somewhat similar to 

 rubber, occurring in the latex of certain East Indian trees. 

 It is obtained and washed like crude rubber and is then a 

 fibrous white to brown mass, tough and inelastic when cold, 

 softening greatly on heating. It is soluble in carbon disul- 

 phide, chloroform, and warm benzine. In composition it 

 is a mixture apparently of a hydrocarbon, CsHg, and two 

 resins which are oxygenated bodies. It is a very poor con- 

 ductor of electricity and finds its principal use as insulating 

 material for wires, etc. 



(c) Chicle is also a product of the coagulated latex of 

 certain South American trees, and is used in the United 

 States in the manufacture of chewing gum. It is composed 

 of a true gum soluble in water, resins, the hydrocarbon of 

 gutta percha, mineral constituents, and some other com- 

 pounds. The purified insoluble portion is used for making 

 chewing gum. 



