INDIA RUBBER AND GUTTA-PERCHA. 687 



ferior grades are dark and mixed with impurities. The former 

 are tenacious, the latter often very friable. Macassar and Sara- 

 wak, the finest grades of gutta, are light-brown verging on yellow, 

 while Balata is rose-brown. 



On being refined and drawn thin, gutta-percha is translucent ; 

 drawn very thin, it is transparent ; but placed on a white surface, 

 it is rose or gray. At ordinary temperatures it is supple, flexible, 

 and very tenacious and extensible, so that it may be drawn to 

 three times its length, when it retains almost all of the extension. 

 If a dent be made with the finger nail, a trace will remain. It 

 softens above 50 C. and becomes adhesive above 100 C. Two 

 pieces may be permanently joined by applying a hot iron to the 

 surfaces and using light pressure. It is a bad conductor of heat 

 and electricity, but may be electrified by friction ; so it is some- 

 times employed for the disks of electric machines. Exposed to 

 the air, it undergoes, at length, a great change, losing its fibrous 

 structure and becoming granular and friable ; more quickly in 

 hot countries. This is a result of the action of oxygen under the 

 influence of light. It is insoluble in water, softens in boiling 

 water and steam ; resists alkalies, hydrofluoric acid (being used 

 for a receptacle for this acid), and ordinary dilute acids, but, when 

 strong, they attack it. 



The property of gutta-percha of greatest value to mankind is 

 its dielectric or nonconducting property. This is not lessened by 

 atmospheric conditions, nor is it destroyed by plunging under 

 water or -burying in the ground or subjection to other deteriorat- 

 ing influences. Hence its fitness for cables, telephone wires, etc. 

 Its power of insulation decreases as the temperature increases. 

 Sea water is a medium in which gutta-percha undergoes no alter- 

 ation, and the enormous pressure at great depths exerts a favor- 

 able action on it by closing up accidental splits. Wrappings are 

 put upon electric cables to protect the insulation from abrasion 

 and the attacks of marine animals, as well as to strengthen the 

 cable. Gutta insulation is preferred for telegraphy, telephony, 

 bell service, etc. ; rubber insulation for lighting and power, as 

 intense currents are liable to lead to accidents by fusion of gutta 

 insulation. What the world owes to gutta-percha may be most 

 easily illustrated by more than one hundred and thirty-nine thou- 

 sand miles of ocean cables, not to speak of the myriads of wires 

 on land, under it, and in buildings for every conceivable purpose. 



As soon as this valuable substance became known, industrial 

 enterprise at once sought to make use of it. From the year 1844 

 the new product received numerous applications and gave rise to 

 many patents. It was used for making stoppers, glues, and wires ; 

 then shoes, surgical instruments, and clothing. The most fortu- 

 nate application was as coating for telegraph cables (patents to 



