148 BELL SYSTEM TECHNICAL JOURNAL 



stability. Wlien properly prepared both of these materials show- 

 practically negligible changes in electrical properties as a result of 

 prolonged submergence in water. Sea bottom conditions are even 

 less likely to affect these materials than those existing in the laboratory. 

 This is because of the absence of light, limited oxygen supply and 

 low temperature, all of which reduce the tendency of materials such as 

 paragutta or gutta percha to oxidize or otherwise deteriorate. It 

 has also been shown ^ that the low temperature and high pressure 

 existing at sea bottom reduce the rate of water absorption but do not 

 materially affect the amount absorbed. 



Electrical Characteristics: The electrical properties of paragutta 

 depend upon the particular composition chosen, the quality of the 

 raw materials and the care exercised in processing them. For long 

 telephone cable insulation, it is necessary to exercise the utmost care 

 to obtain a material having dielectric constant and specific conductance 

 values sufficiently low to reduce to the minimum its effect on the 

 attenuation. On the other hand, for ordinary telegraph cables these 

 values are less critical and it may be advantageous to modify the 

 practice for purposes of economy. Representative values for the 

 electrical properties of a superior grade of paragutta and typical cable 

 gutta percha under sea bottom conditions are given in Table III. It 

 will be seen in this table that paragutta has a 20 per cent low^er dielec- 

 tric constant and a specific conductance one-thirtieth that of ordinary 

 cable gutta percha under sea bottom conditions. The insulation 

 resistance and dielectric strength of the two materials are practically 



the same. 



TABLE III 



Comparative Electrical Properties of Paragutta and Cable Gutta Percha 

 AT Sea Bottom Conditions 



Specific Inductive Effective A-C 



Capacity 2° C. Conductivity 2° C, 



400 Atm., 2000 Cycles 400 Atm., 2000 Cycles 



Unit = 10-12 mho. cm. 



Cable Gutta Percha 3.3 90 



Paragutta 2.6 3 



Acknowledgment 



The author wishes to acknowledge his indebtedness to Mr. R. R. 

 Williams for counsel and assistance during the prosecution of the 

 work and writing of the paper. 



