RESINS 287 
and various industrial arts; and, thanks to him, manufac- 
turers soon came to realize that it was better adapted for 
certain purposes than any other substance. 
Among the more important or familiar applications of 
gutta-percha may be mentioned its use as waterproof ma- 
terial in boot-soles, and as cement for leather, ete., its use 
for piping, for speaking tubes, various 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 prevent serious leakage of electricity. 
77. Resins, like elastic gums, are derived from liquids 
exuded by plants, and serve as a protective covering for 
wounds. The common resin obtained from the pitch or 
turpentine of pines is a familiar example. More 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 liquids mentioned, at least 
when hot. Sometimes a gum and a resin are intimately 
united, forming what is known as a “gum-resin.”’ Such a 
material is asafetida, which we have already studied. The 
name “gum” is also applied 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 likely 
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 different oxidized hydrocarbons which agree in being 
