The Sun.
London, England, 1859-06-24 00:00:00

SUBMARINE TEI,EGRAPHS.

TO THE EDITOR •OF 'THE SUN.

SIR,—As everything relating to submarine tele-
graphs possesses at this moment a public interest,
I venture to send you a few facts on this important
subject.
Assuming a cable to be safely submerged to a
depth of three miles, and its electrical condition
not impaired, we must now consider what mecha-
nical effect such, a pressure of water produces on
the insulator. From practical tests I have made
on portions of the Atlantic telegraph cable (sup-
plied with a potassium wire in lieu of copper), I
discovered by immersing it in water for a continu-
ous period of 23 weeks, and subjecting it to a pres-
sure of three tons per square inch, that it was per-
fectly insulated; but, from this date, the insulator
appeared to deteriorate, and at the 25th week, dis-
covered that moisture had reached the centre of the
core, consequently decomposing the potassium. To
obviate this difficulty I immersed fresh pieces of
cable in bisulphuret of carbon and the chloride of
sulphur, which had the effect of shrinking and
closing up the pores, and rendering the insulator
thoroughly impervious to moisture ; this, in fact,
vulcanised the insulating core to about 1-16th of
its own thickness. Having proved by experiments
that my system of preserving the insu Latin gmedium
from moisture is effectual, I beg to bring such a
valuable fact to your notice.
The result of these trials was brought forward
at a meeting of the Institution of Civil Engineers
prior to the laying down of the Atlantic cable, and
with the view of deterring the Atlantic Telegraph
Company from sinking their cable in its then in-
efficient.state.
The subject was discussed at a meeting of the
company, but unfortunately it was overuled by Mr.
Whitehouse, the company's electrician, although
the fact of such inefficiency was apparent to all
practical men.
The result of applying such a cable for deep-sea
purposes proves the accuracy of my experiments,
but at a loss of from £400,000 to £500,000.
The main 'practical part to be considered in the
construction of telegraphic cables is, combined with
sufficient strength, perpetual isolation. It is not
by outer coverings of tarred and greased hempen
twine, or such soft materials, that will. assist in
rendering the core perfectly insulated, but by apply-
ing to the insulating material, whether fillets, or
coverings of indiarubber or gutta percha, a pressure
of four tosix tons per inch, at the time it is encased
round the copper. conductor. This pressure is ob-
tained by passing the conductor between a series of
double rollers, and to prevent abrasion fibres are
incorporated in the outer coating of the insulating
material, producing a body of such consistency and
power of resistance to alteration of form that alone
is not inherent with the pure insulating substance,
such as gutta-percha or indiarubber.
The adoption of the above means of constructing
telegraphic cables will necessarily produce the fol-
lowing inevitable results :-1. As gutta-percha and
indiarubber decompose, absorb moisture, and are
injured by heat, which, in long lengths of tele-
graphic cables, greatly reduce their insulating
properties, and which have been the great cause of
failure, the cold vulcanising renders the insulating
core homogeneous, shrinkin g and closing up all pores
and joints, besides rendering the insulator oroof
against moisture, decomposition, abrasion, or injury,
by tropical heats. _ .
2d. The great advantsge of laying on
the coatings or fillets of
.indiarubber, longitu-
dinally, and submitting them to cold vulcanisa-
tion, must be apparent to all, over the ex-
pensive and ineffectual system of spirally winding
them round the wire, making a join every quarter
of an inch, or 253,443 joins in a mile, which are
the elements of its own destruction:
3d. The rapid rate at which these cables can be
made will reduce the expense 25 per cent.
4th.
,From, their lightness and great longitudinal
strength there will be little or no strain upon the
conductor; therefore the paying-out apparatus will
be simple and inexpensive.
sth. Telegraphic wires , insulated with india-
rubber, and subjected to cold vulcanisation, will
resist 250 degrees of heat, and may be punctured 50
times in the space of an inch without admitting any
water to the wire, from its superior power of elastic
contraction caused by. vulcanisation. To the publio
this is a matter of the Atlantic
importance, inasmuch
as one pin-hole in'the Atlantic cable would render
it unserviceable.

In conclusion, I believe that a cable constructed
on these principles will eventually be the only one
capable of permanently resisting the severe natural
actions to which all submarine wires are subject,
when submerg&l at great lengths and depths.
I may add that I have met with the same diffi-
culty in introducing the above system of construct-
ing telegraphic cables that I did twenty years ago,
in i ntroducing powerful, metallic rollers for the
coating of cloth with indiarubber, and vulcanising
the surface, first employed by me at the Tottenham
Indiarubber Mills (then known as the London
Caoutchouc Company), and now universally adopted.
The coating of, telegraphic wires with india-
rubber is but a simple affair compared to coating
cloth two yards wide ; suitable machinery (which
is being constructed) will coat 'from 250 to 300
miles of perfect vulcanised cable per day.—l am, &c.
JOHN MACINTOSH.