Page:Popular Science Monthly Volume 50.djvu/709

Rh works upon the subject.) Nor was it until January 10, 1849, some months later, that Walker, one of the first savants that busied themselves with electricity, and who first experimented with the railway block-system, successfully telegraphed in the harbor of Folkestone on what is generally considered the first submarine cable. It was a gutta-covered cable extending from a boat two miles to the shore. The favorable results at Folkestone encouraged John W. Brett, who is known in England as the father of submarine telegraphy, to construct the first long line from Dover to Calais, with the encouragement of the French Government, in 1850, when the successful application of gutta-percha to real submarine telegraphy was demonstrated and Wheatstone's hopes were completely realized. Brett labored with great energy for the success of long-distance submarine communication, and his faith and advice, as well as capital, were of the very greatest value to Field and his fellow-promoters of the first Atlantic cables. In 1851 the fire-hose at the exposition in London was of this substance, and on the last voyage in search of Franklin a light and portable gutta-percha boat did good service, showing that the material was suitable for the sheathing of boats. Advantageous use was also made of it in making molds for reproducing delicate impresions in the galvanoplastic process. But, except in telegraphy and galvanoplasty, its employment soon diminished. Shoes of gutta-percha softened before the fire and stuck; clothing made of it in turn fell into ill favor. Vulcanizing and mixing with rubber were thought of, but still satisfactory products were not obtained. They were hard and were soon abandoned.

The failure of gutta-percha for some purposes is owing to its greater suppleness at a slightly elevated temperature. It may be vulcanized by adding sulphur and heating to 135° to 150° C, but this process, owing to inconvenient results obtained, is now very rarely employed. Its resistance to acids led to its being put to use for vessels and tubes in factories of chemical products and laboratories, while medical science, as seemed promised at its coming, has found in it a valuable auxiliary.

The gutta-percha of commerce contains impurities—wood, earth, sand, etc.—which must be eliminated. It may be dissolved in sulphide of carbon or benzene. Then decant and allow to evaporate. A cheaper and preferred method is by mechanical means. The cakes are cut into chips, which are plunged into a hot-water vat and stirred by an agitator; the heavy substances go to the bottom, the gutta and wood remaining on top. A series of rasps removes the wood, and the gutta is taken and dried. The process is often accomplished by still other machinery for removing the foreign substances, care being taken to squeeze out all the air bubbles. The gutta is now pure, but may be mixed with