628 Original Articles. { Oct. 
requirements in any insulating substance is that it should offer facili- 
ties for making the numerous joints required, either in the first con- 
struction of the line or for its repair when laid down. For this 
purpose, also, india-rubber appeared well adapted : if after being cut 
the fresh surfaces are immediately brought into contact, almost perfect 
reunion takes place ; and if they are warmed and slightly moistened 
with naphtha (in which india-rubber is soluble), they are hermetically 
sealed. The covering was effected by first coating the copper wire 
with cotton and shellac varnish, and then winding a thin strip of 
masticated india-rubber spirally round the wire, each turn overlapping 
the last. Several coatings were thus put on, the union of the surfaces 
being secured by means of naphtha. An almost perfect insulation 
was the first result, the problem on which so much time and money 
had been expended seemed to be definitely solved, and the new material 
came into rapid use. A short time, however, showed the fallacy of 
these hopes. India-rubber, like all other gum-resins of a similar 
character, slowly burns or oxidizes in the air, even in darkness; but 
when exposed openly to the weather and to sunlight this oxidization 
goes on with alarming rapidity ; wires hung out of doors soon become 
useless; the india-rubber assumed a thick gummy or semi-fluid 
character, and soon fell away from the wire. The joint, even when 
made with naphtha, was found not to be durable, and after a short 
time, even in unexposed situations, the coating was found loose upon 
the wire. Attempts were made to preserve it by enclosing it in 
grooved boards, and thus protecting it from the air, but in dry situa- 
tions this was found to be of but little avail; and although in wet 
tunnels it was found to add to the durability, it was ultimately obliged 
to be abandoned there also. 
Gutta-percha was soon proposed asa remedy for these evils. When 
pure, and at moderate temperatures, it is a remarkably good insulator, 
and, moreover, is capable of being kneaded and drawn solidly on the 
wire through dies, thus avoiding the infinite number of joints required 
when india-rubber is used. From an analysis by Professor W. A. 
Miller, it appears that pure gutta-percha is a hydro-carbon, consist- 
ing of — 
Carbone fy.) poo u6 
Hydrogen . . . 11:04 
100-00 
In commerce, however, it is mixed with resin, vegetable fibre, 
moisture, &c.; the latter being mechanically diffused through the 
mass, influencing its pliability and toughness. Commercial gutta- 
percha will remain unchanged for months in the air, provided light be 
excluded, and the temperature be not very high; and it will remain 
unaltered for years in water, especially if coated with Stockholm tar, 
and kept in the dark. It is, however, rapidly destroyed by alternated 
exposure to a moist and dry atmosphere, especially if the sun’s rays have 
access to it. Professor Miller found that all the deteriorated portions 
had absorbed oxygen. 
