Page:The American Cyclopædia (1879) Volume VIII.djvu/358

 GUTTA PERCHA tains from 75 to 82 per cent, of pure gutta, the remainder being composed of the two resins just mentioned. The treatment of gutta per- cha is similar to that already described under CAOUTCHOUC. The first process is to purify it of the foreign substances, as earth, stones, and sticks, with which it is contaminated. For this purpose the blocks are sliced, by knives attached to powerful wheels, into shavings. These are introduced into a large tank of water heated by escape steam to boiling. The gum softens and runs together, and by the boil- ing most of the impurities separate and sub- side. The mass is then removed to a machine called a teaser, which is a large box containing a drum armed with rows of crooked teeth. This, revolving rapidly, tears the gum into shreds, which fall into a vessel of water, in which it floats, and the remaining impurities subside. The purified fragments are again boiled ; they again run into a soft mass, and this is taken into the kneading or masticating machine, which is a strong cast-iron box con- taining a revolving cast-iron drum armed with strong iron teeth ; or instead of the drum, two parallel rollers with screws on their surface are employed. Steam is let into the machine, and the gutta percha, kept soft by its heat, is thor- oughly kneaded and brought to uniform con- sistency without air or water in the mass. It is then ready to be rolled into sheets or pressed into tubes; the former in their various sizes and thicknesses furnish the article in shapes convenient of application to most of the uses to which it is adapted. Tubes are produced by forcing the kneaded mass through a steel cylinder which terminates in a mould with a circular metallic core. Passing through this, the soft substance is prevented from col- lapsing by being drawn through a long chan- nel of water by the revolution of a drum at the other extremity of the canal. By continually supplying the material the tubes are made without interruption ; and in this way a single length has been produced of 1,000 ft. These tubes by their remarkable strength are well adapted for resisting great pressures ; they are used for aqueducts, for feed pipes of steam engines, for hose, pump barrels, and va- rious other purposes connected with the con- veyance of water, gases, and vapors. The first machinery built for the coating of telegraph wire with gutta percha was in the autumn of 1848, at the works of the American gutta per- cha company in Brooklyn. The first order for the prepared wire was for the Morse telegraph company, and it was laid across the Hud- son river at Fort Lee in August, 1849. The gutta percha employed was prepared with the greatest care to insure its purity. The rasp- ings, rolled and then macerated in hot water, were washed in cold water, and then, being softened by boiling water, were driven by hy- draulic apparatus through cylinders, in the end of which were wire-gauze sieves. After this the substance was thoroughly masticated and kneaded, by which it was entirely deprived of moisture and rendered homogeneous and com- pact ; and it was then introduced into the long horizontal cylinders kept hot by steam, and powerfully compressed by screw pistons worked by machinery. As it was forced out at the extremity the gutta percha was made to pass through a die, in which the strand of copper wires was introduced, and the whole was drawn along by a revolving drum upon which it was wound. A second and third layer of gutta percha were added to the core by repe- titions of the process. Mr. Charles Goodyear applied the same process to moulding various articles in gutta percha, attaching the moulds, which were of metal in several pieces securely bolted together, to the end of the cylinder, through which the plastic gum was forced. Holes were left for the escape of the air in the moulds, and the appearance of the gutta per- cha at these indicated the completion of the filling. Gutta percha is often used in combi- nation with caoutchouc, the latter serving to soften and render the material more pliable and elastic, and less liable to be affected by changes of temperature. Both are alike affect- ed by the treatment called vulcanizing, which is thoroughly mixing the gum with sulphur or some of its compounds, and then subjecting the mixture to an elevated temperature in close vessels. (See CAOUTCHOUC.) The methods and materials employed for vulcanizing gutta per- cha are numerous, and the object desired is not always the same. A hard horny material is produced under the patent of Mr. Stephen Moulton, by mixing the gum with hyposulphite of lead and adding more or less of calcined magnesia, and then subjecting the compound to a temperature of 250 to 300 for some hours. Mr. Hancock in his patent of 1847 em- ployed a mixture of 48 parts of gutta percha with 6 parts of sulphuret of antimony, sulphu- ret of calcium, or some other similar sulphu- ret, and 1 part of sulphur. Mr. Emory Rider of London in 1856 patented an improvement which consisted in the addition of 1 part of litharge to 66 parts of gutta percha, together with 1 part of sulphur, or its equivalent in some of its compounds. These substances are mixed and well incorporated into the plastic gum by the action of heated rollers, which, re- volving at different speeds, powerfully wear and grind the material ; after which, in a close metallic vessel one third filled, it is subjected to the vulcanizing temperature for a few hours. The patents for mixing gutta percha with other substances are too numerous to be particularly noticed ; even these substances are almost in- numerable. The object of these various mix- tures is to produce materials of different de- grees of hardness and of different capacities of resistance to changes of temperature and other causes of change, but which may still be mould- ed into and retain the form of useful articles. The principal use of gutta percha is for cover- ing telegraph cables. It is also used by den-