1864. | Farrearrn on Submarine Telegraph Cables. 635 
sulators. Recourse was had to 
the small cylinder, ¢, Fig.3,which FIG .3 
was surrounded by the water- 
bath, b,b, maintained at a uniform 
temperature of 100° Fahr. by the 
gas-jet g. t,t, is the thermometer. 
The lever by which the pressure 
was applied to the plunger is 
shown at 1, L, attached to the 
firm cast-iron base, A, A. 
The different substances were 
tried separately, as in the first 
series, and the weighings were 
repeated at intervals. During 
the night it was necessary to 
remove the gas jet, as the uni- 
formity of temperature could not 
be depended upon; hence, for 
half the period of immersion the 
specimens were at a temperature 
of 50° only, and for the remain- 
der at a temperature of 100°. The 
loss of weight, after removal 
from the cylinder, in conse- 
quence of the evaporation of the 
water absorbed, was, in these 
experiments, noted, and it was 
found the specimens decreased 
in weight below their original 
weight when dry. 
In the whole of these experi- 
ments, the pressure was 20,000 
lbs. per square inch; area of 
specimens, 8 square inches; and 
thickness, about one-eighth of an 
inch. 
Tasie 1V.—Fourth Series of Experiments on Absorption, at Increased Temperatures. 
Results reduced to 100 hours and 10 inches area. 
3 Bie s| 
vies _ yael ol) deter! oa ts! = 
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38 INSULATORS, 5 oe sme \3 ez Eg | ae 
3 | Gutta-percha . . . . | 20,000] 100] 75° | 10 | 0-27 | 3-61 
+ India-rubber .. . - | 20,000 100 | 75 10 | 0:45 | 0:87 
5 Wray’s compound , . . | 20,000} 100| 75 10 | 0°58 | 0°91 
6 Chatterton’s compound . | 20,000 | 100 | 75 10 | 0-20 | 0°60 
i Vulcanized rubber . . | 20,000] 100] 75 | 10 | 0°80 | 2:27 
| 
