EESIXS 287 



ancl various industrial arts; and, thanks to him, manufar'- 

 turcrs soon came to realize that it was better adapted for 

 certain purposes than any other sul)stancc. 



Among the more important or familiar apj^lications of 

 gutta-percha maj' lie mentioned its use as waterproof ma- 

 terial in boot-soles, and as cement for leather, etc., its use 

 for piping, for speaking tubes, ^-arious surgical appliances, 

 golf balls, and molded ornaments. Its most important use 

 is as insulating material for electric wires, especially cables. 

 The great Atlantic cables and other submarine or subter- 

 ranean electric lines, upon which modern civilization so 

 much depends, owe their successful operation largely to the 

 gutta-percha used to cover the wires and so protect them and 

 at the same time pre^'ent serious leakage of electricity. 



77. Resins, like elastic gums, are derived from liciuids 

 exuded by plants, and serve as a protective covering for 

 ■u'ounds. The common resin obtained from the pitch or 

 turpentine of pines is a familiar example. JMore or less fluid 

 at first, owing to the presence of volatile oil, the resinous sap 

 solidifies on exposure to the air, partly through evaporation 

 of the volatile constituent and partly through its oxidation. 

 Finally it may become hard and brittle. In this condition 

 resins resemble various gums. But true gums, as we have 

 seen, are either soluble in water or absorb it indefinitely; 

 while they are insoluble in ether, alcohol, carbon bisulphid, 

 and oils. Resins, on the contrary, are insoluble in water; but 

 are mostly soluble in the other hquicls mentioned, at least 

 when hot. Sometimes a gum and a resin are intimately 

 united, forming what is known as a " gum-resm." Such a 

 material is asafetida, which we have already studied. The 

 name "gum" is also apphed commercially to gum-resins, 

 and resins, and even to rubbery materials; it is most con- 

 venient, however, to restrict the term as indicated above, 

 except for "elastic gums" from which no confusion is Hkely 

 to arise. When a considerable amount of volatile oil is asso- 

 ciated with a resin the mixture (commonly of a honey-like 

 consistency as in the turpentine of pines and firs) is distin- 

 guished as an oleoresin. Resins are always mixtures of sev- 

 eral chfferent oxidized hydrocarbons which agree in being 



