The Sun.
London, England, 1859-04-23 00:00:00

SUBMA.RINE TELEGRAPHS.

Some interesting and valuable experiments have
recently been made at Silvertown, the manufactory
of Messrs. Silver and Co., the outfitters, with a view
of displaying the advantages gained by substituting
indiarubber for gutta percha as an insulator for
submarine wires. The tests were principally con-
ducted to prove that, in an electrical point of view,
indiarubber was as gbod a non-conducting medium
as gutta percha, while in all the requisites of with-
standing great heat and the most dense pressure it
was incomparably superior. When the first sub-
marine cables were commenced, in 1841, gutta
percha was unknown in England, and indiarubber
only was employed as a means in insulatinghothweecvoenr:
ductor. The great variety of purposes,
for which indiarubber was then used made the de-
mand for it so great as to render not only its cost
high, but the amount of its production uncertain.
The properties of gutta percha soon afterwards be-
came known, and-on its first introduction to this
country, at a comparatively low price, it was found
to be a cheaper medium of insulation, and one ap-
parently equally efficacious with indiarubber.
Its
adoption as a covering for submarine cables, there-
fore, soon became general, and has continued with
little interruption down to the present day. But
during the time that has intervened since india-
rubber was first given up for the new material, the
conditions of cost between the gutta percha and
indiarubber have been entirely reversed, while im-
mense progress has been made in the knowledge of
all matters relating to submarine telegraphy The
The
result of this increased experience -has Len to
plane beyond a doubt that many better insulat-
ing mediums than gutta percha can be found,
which at less than half the cost will work twice as
well. No doubt, scientific research upon this matter
has been keenly stimulated by observing how inju-
riously the Gutta Pereha Company's Virtual mono-
poly has acted upon the interests of all submarine
telegraphs. To this company alone belongs the
right of making and selling gutta percha in any
way or form whatsoever. They raise or lower the
price of the material at will, and from their charges
there is no appeal. It any enterprising member of
the House of Commons wishes for the strongest
illustration to be found in this country of the evils
which result to enterprise from these patent mono-
polies, he has only to inquire into the privilege-3
enjoyed by the Gutta Percha Company, and then
see how these have acted upon the cause of tele-
graphy throughout the kingdom. The present price
of gutta percha is 2s. 6d. per lb., and this immense
cost, coupled with its now well-known deficiencies
as an insulator, has roused the chemical world into
efforts to discover some substitute which, while
possessing all non-electrical and mechanical essen-
tials, will at the same time relieve telegraph com-
panies from the monstrous outlay now required for
coating their wires with gutta percha. Several
experiments have been made with this object, and
some of them have resulted in the triumphant suc-
cess, as regards elasticity, cost, lightness, and
rapidity of production, of the new materials.
Messrs. Silver and Co. have been foremost among
the experimentalists, but, instead of devising a new
substance, have resolved to trust the well-known
properties of indiarubber, and with this view have
coated several miles of wire with a double layer of
that material laid on in spiral folds or bands, with
their edges closely joined so as to be perfectly
impervious to water at any pressure. Even at the
present high price of indiarubber wires can be thus
coated at very little more than half the price
charge for gutta percha. The cost, however, is one
of the least advantages of the material. Every one
knows how elastic indiarubber is, but every one
does not know that it is almost as incompressible as
water, and compared with gutta percha requires a
very great heat to melt it, boiling water having no
effect upon it whatever. Some lengths of the wire
thus coated at Messrs. Silver's works have been
subjected in a hydraulic machine, for a consider-
able time, to a pressure of 7A- tons on the circular
inch, and when tested, while still exposed to this
pressure, the most sensitive of Mr. Henley's gal-
vanometers showed the insulation perfect. An
attempt to apply a higher rate of pressure than
this terminated, as might have been expected, in
the bursting of the hydraulic cylinder under the
tremendous strain. When it is recollected that
five tons pressure to the square inch crushes granite,
it will be seen that a more complete test of the
value of indiarubber as an insulator to resist pres-
sure could hardly have been devised. The import-
ance of its possessing this quality is far greater
than would at first sight be supposed. A pressure
of 71 tons to the inch is equal to the pressure caused
by the weight of water at a depth of eight miles.
The greatest depth at which the Atlantic cable was
submerged was three miles, and the weight of this
mass of water upon the rope at the bottom of the
sea was about 21 tons. Gutta percha at such a
pressure is reduced to less than half its bulk. To
this apparently insignificant fact it is doubtless
owing that the cable is now useless, for it follows
as a matter of course, that when the core of the rope
shrank to half its original diameter the outside
wires stretched in proportion, while the gutta
percha could not but tear under the strain, and
leave the conductor exposed in many places. The
advantage, therefore, of indiarubber over gutta
percha in this respect is at once apparent, since it
exactly reverses the unfavourable conditions of the
latter, being incompressible and highly elastic.
With regard to withstanding heat, its superiority
is equally great. During the course of the experi-
ments a considerable length of wire insulated with
two coats of indiarubber was immersed in a large
boiler of boiling water. Though the external part
of the covering was boiled almost white, the insula-
tion remained perfect. A similar length of wire
coated with gully percha of the same thickness as
the indiarubber was, of course, destroyed as a
non-conductor immediately on its immersion, as
gutta percha melts easily at 100 degrees. It is,
of course, very true that submarine cables when
laid are not required to encounter a beat
of 212 degrees, but it is well known that
while in process of manufacture, and especially when
packed in ships' holds for the purpose of being sub-
merged, they are often exposed to an amount of
heat to which gutta percha yields. This melting at
a low temperature, together with the wire being
badly centred at the Gutta Percha Company's
works, was a source of incessant anxiety to those
on board the Agamemnon and Niagara during the
expedition of last summer. The deck coils, from
being exposed to the sun, were more liable than
others to danger, and some portions of them had to
be cut out in consequence of the copper wire having
pushedthrough the soft gutta percha. On both these
important points, therefore, the introduction of
indiarubber would be of immense benefit, and we
believe if it was once clearly shown that the supply
of material might be depended on, and the rate at
which wires could be covered would be equal to the
demand, it would soon entirely supersede gutta
percha as a means of insulation. Experiments are
also being carried out by another firm for the pur-
pose of devising an insulator from a combination of
indiarubber and shellac. These tests, however, are
not sufficiently advanced to be made public, though
the results up to the present give promise of the
most complete success. When such efforts are mak-
ing on all sides, it seems improbable that the use of
a faulty and expensive insulator like gutta percha
will be much longer continued.