PARAGUTTA, A NEW INSULATING MATERIAL 



143 



facture, laying and repairing and possibly at times during use, espe- 

 cially where tidal currents may cause movement in the cable. Para- 

 gutta and gutta percha cores have been subjected to slow and con- 

 tinuous flexing at 0° and 25° C. for long periods and it was found that 

 both materials will withstand millions of repeated flexures at small 

 amplitudes without failure. When the amplitude of flexure was 

 increased to strain the conductor slightly beyond its elastic limit, 

 the conductor always failed in advance of the insulation. 



Plasticity Tests: Laboratory tests were made to determine the rela- 

 tive plasticity of paragutta and gutta percha, using both the Williams ^ 



9 100 



40 60 



COMPRESSION-PER CENT 



100 



Fig. 6 — Comparative compression properties of paragutta and gutta percha at 25° C. 



and the Marzetti ^ type of plastometers. These tests are valuable 

 guides but the final judgment of a material as regards thermoplasticity 

 was made by determining its workability on commercial gutta percha 

 insulating machines. Paragutta is somewhat more resistant to flow 

 than gutta percha at temperatures ranging from about 40° to 70° C. 

 When applied to the conductor, however, its greater resistance to flow 

 at elevated temperatures can be taken as an advantage as it lessens 

 the danger of faults occurring if the core should be accidentally exposed 

 to elevated temperatures or to conditions which might exist in con- 

 nection with cable used in the tropics. 



* Williams, Jour. Ind. & Engg. Chem., 16, 262 (1924). 

 ^ Marzetti, Giorn. Chitn. Ind. Applicata, 5, 342 (1923). 



