SUBMARINE TELEGRAPHS.

Daily Southern Cross, Volume XVI, Issue 1242, 9 August 1859, Page 2 (Supplement)

SUBMARINE 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 india rubber for gutta percha as an insulator for submarine wires. The tests were principally conducted i to prove that, in anelectrical point of view, india rubber was as good a non-conducting medium as gutta percha, while in all the requisites of withstanding great heat and the most dense ptessure it ,was incomparably superior. When the first submarine cables were commenced, in 18 H, gutta percha was unknown in England, and india rubber only was' emploged as a means ot insulating the conductor. The great variety ,of purposes however for which india rubber was then used made the demand 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 became known, and on its first introduction to this country, at a comparatively low price, it was found to be a (heaper medium of insulation, and apparently equally efficacious with india rubber. Its adoption as a covering for submarine cables, therefore, soon became genera), and has continued with 1-ttle 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 ot cost between gutta percha and india rubber have been entirely reversed, while immense progress has been made in the knowledge of *U matters relating to submarine telegraphy. The result of this increased experience has been to place beyond a doubt that many better insulating mediums than gutta percha can be found, which at less than halftne cost will work twice as well. No doubt, scientific research upon this matter has been keenly stimulated by observing how injuriously the Gutta Percha Company's virtual monopoly 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, if any enterpri«ing 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 monopolies, he has only to inquire into the privileges enjoyed by the Gutta Percha Company, nnd then see how these have acted upon the cause of telegraphy throughout the kingdom. The present price of gutta percha is 2s 6d. per lb., and this immence cost, coupled with its now well known deficiencies as an insulator, has roused the chymical world into efforts to discover* some substitute which, while possessing all non-electrical and mechanical essentials, will at the same time relieve telegraph companies from the monstrous outlay now required forco.iting their wires with gutta percha. Several experments have been made with this object, and some of them have resulted in the most triumphant success, as regards elasticity, cost, lightness, and rapidity of production, of the new materials. Messrs. Silver and Co. have been foremost among tlie experimentalists, but, instead of devising a new substance, have resolved to trust the well-known properties of india rubber, 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 india rubber, wires can be thus coated at very little more than half the price charged for gutta percha. The cost, however, is one of the least advantages of the material. Every one knows how elastic india rubber is, but every one-does not know that it is almost as incompressible as water, and compared with gutta percha requires a very high degree of 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 considerable time, to a pressure of 7? tsns on the circular inch, and when tested, while still exposed to this pressure, the most sensitive of Mr. Henley's galvanometers showed the insulation perfect. An attempt to apply a higher rale 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 5 tons pressure to the square inch crushes granite, it will be seen that a more complete test of the value of india rubber as an insulator to resist pressure could hardly have been devised. The importance of its possessing this quality is far greater than would at first sight be supposed. A pressure of 7£ 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 2£ tons. Gutta percha at such a pressure is reduced to less than half its bulk. To this apparently insignificant fact is it 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 india rubber 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 preat. During the course of the experiments a considerable length of wire, insulated with twu coats of india rubber, was immersed in a large boiler of boiling water. Though the external part of the covering was .boiled almost white, the insulation remained perfect. A similar length of wire, coated with gutta percha of the same thickness as the india rubber was. of course, destroyed as a non-conductor immediately on its immersion, as gutta percha melts easily 1 at 100 degrees. . It is, of course, very true that submarine cables when laid are not required to encounter a heat of 212 degrees, but it is well known that while in process ot manufacture, and especially when packed in ships' holds for the purpose of being submerged, 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 this danger, and some portions of them had to be cut in consequence of the copper wire having pushed through the soft gutta percha. On both these important points, therefore, the introduction of india rubber 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 purpose of devising an insulator from a combinytion of insulator 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 making on all sides, it seems improbable that the use of a faulty and expensive insulator like gutta percha will be much longer continued.