95 



liquid or suspended globules to solid rubber (coagulation) can 

 be hastened by heat and by stirring. 



It may be mentioned that gutta-percha is also obtained from 

 the latex of certain trees growing wild in the Malayan peninsula. 

 This is plastic when heated but is not elastic like rubber. An- 

 other latex plant is the Sapodilla plum of the American tropics 

 which yields the chicle used in making chewing gum. 



History of the Use of Rubber 



The ancient peoples of India and China used rubber, chiefly 

 obtained from wild trees of a kind of fig, the plant many of you 

 know as the rubber plant which is frequently grown as a house 

 ornamental. Soon after the discovery of America the Spaniards 

 found certain Indian tribes playing a game with a ball that was 

 elastic and would boiind. Columbus himself took some of these 

 balls back to Spain. About the year 1770 the noted English 

 chemist. Priestly, found that this elastic substance would rub 

 out pencil marks and so he named it rub-ber. Soon thereafter 

 one inch "rubbers" sold for three shillings each. 



The native peoples of tropical America utilized rubber by 

 spreading it over cloth, or over foot-wear, and at first the white 

 man imitated this process. A Scotchman named Mcintosh 

 learned to dissolve rubber in naphtha and then spread it on or 

 between cloth. But clothing and shoes coated with rubber 

 became soft and sticky in hot weather or in warm rooms, and 

 brittle and hard during cold weather. So rubber was of little 

 use to mankind until a Connecticut hardware merchant, named 

 Goodyear, after long tedious study and experimentation, learned 

 in 1839 to vulcanize rubber. At that time only a few tons of 

 rubber were used each year, but with this discovery the use of 

 rubber soon absorbed several thousands of tons yearly. Seldom 

 do we stop to think when we put on our goloshes on a rainy 

 morning that for something like 5,000 years of history our 

 ancestors went without such a protection from wet feet. 



The Principal Rubber Plants 



The world's supply of rubber comes chiefly from the Par4 

 rubber tree (Hevea brasiliensis) , of which enormous forests exist 

 in South America. This tree has been planted with success in 



