OILS AND FATS. 375 



pieces of it, embalmed, as we may say, centuries upon cent- 

 uries before the Egyptians lived whose mummies are found 

 in the pyramids. 



528. Uses of the Resins. The resins are chiefly used for 

 making varnishes. In spirit varnishes the solvent is alco- 

 hol ; in oil varnishes it is some drying oil. As the resins 

 are soluble in fat oils, they enter into the composition of 

 many ointments and plasters. Sealing-wax is mostly the 

 resin called shellac, with a little turpentine to make it melt 

 and burn more readily, and some cinnabar, lampblack, or 

 other substance to color it. 



529. Caoutchouc and Gutta-Percha. These are mixtures 

 of several hydrocarbons, and are in their composition very 

 much like turpentine oil. The caoutchouc is the milky 

 juice which exudes from incisions made in several kinds 

 of large trees in South America. This, when left to dry in 

 the air, becomes a white elastic mass. The drying is more 

 rapid when the exuded substance is spread upon moulds 

 of clay and suspended over a fire, as is commonly done. 

 The soot, which thus becomes incorporated with it, gives 

 it a dark color. Gutta-percha is obtained from certain trees 

 in the East Indies. Like the caoutchouc, it exudes as a 

 milky juice. It differs from caoutchouc in three respects 

 it is very tough, has little elasticity, and becomes soft 

 and plastic with a moderate heat, hardening again as it 

 grows cool. This difference in properties fits these two 

 substances for different uses in the arts. 



530. Vulcanized India-Rubber. This substance is a com- 

 pound of sulphur and caoutchouc, which has received pecul- 

 iar qualities from being subjected to a certain degree of 

 heat. Unless this be done it is too soft for use. Shoes 

 and other articles of this material are therefore, after being 

 made, brought up to the required temperature, and on cool- 

 ing they have the two qualities of firmness and pliability. 



