99 
1864. | Farrparrn on Submarine Telegraph Cables. 633 
These tables show that, of all the substances tried, native unmas- 
ticated india-rubber absorbs by far the most water. 'The whole surface 
of the specimen had lost its black colour, and become whitened during 
the experiment. Taking the mean of three experiments very closely 
agreeing, we find that native india-rubber, after manufacture, absorbs 
less water than in its native state, in the proportion 0°682 to 3:07, 
or 1:43. Vulcanized india-rubber appears to be the least absorbent 
substance tried, but when combined with carbon, it absorbs nearly one- 
third more water (according to the results in this table) than in its 
pure masticated state. Gutta-percha and Chatterton’s compound are 
nearly alike in their resistance to absorption, the latter beg superior. 
In these experiments they increased in weight only one-half as much 
as pure india-rubber (masticated), and twice as much as vulcanized 
india-rubber. Wray’s compound absorbed rather more than masticated 
india-rubber. Marine glue lost instead of increasing its weight. 
Comparing these experiments with the last, we find that these 
materials are far from following a law of simple proportion in the 
amount of water absorbed in different times. The present experiments 
were made under a pressure of 5,900 Ibs. per square inch, and lasted 
for a period of 450 hours. The last were made under a pressure of 
20,000 Ibs., and lasted less than 100 hours. In the present experi- 
ments, carbonized india-rubber absorbed seventeen times as much as in 
the former; Wray’s compound, ten times; gutta-percha, seven times ; 
and masticated india-rubber, only four times. Hence it appears that, 
other things being equal, masticated india-rubber would be most 
advantageous, and carbonized: india-rubber least so, as insulators ; 
because, so far as these experiments afford data for generalizing, 
masticated india-rubber follows a rate of absorption diminishing most 
with time, and carbonized india-rubber least so. This deduction, how- 
ever, is complicated by the fact of a difference of pressure, and possibly 
of temperature, in the two experiments. 
The order of merit in resisting absorption, as derived from this 
series of experiments, is— 
1. Vulcanized india-rubber. 
2. Chatterton’s compound. 
3. Gutta-percha. 
4, Masticated india-rubber. 
5. Wray’s compound. 
6. Carbonized india-rubber. 
7. India-rubber not masticated. 
The next series of experiments was made under greater pressure, 
- but in the same manner and for the same period of immersion. 
