Makers of Many Things

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To make an overshoe, the rubber is run through rollers and formed into thick sheets for soles and thinner sheets for uppers. Another machine coats with gum the cloth used for lining and stays. Rubber and rubber-lined cloth go to the cutting-room, where all the different parts of the shoes are cut out. They are then put together and varnished. While still on the last, they are dipped into a tank of varnish and vulcanized--a very simple matter now that Goodyear has shown us how, for they are merely left in large, thoroughly heated ovens for eight or ten hours. The rubber shoe or boot is now elastic, strong, waterproof, ready for any temperature, and so firmly cemented together with rubber cement that it is practically all in one piece.

During the last few years there have been frequent calls from various charities for old rubber overshoes, pieces of rubber hose, etc. These are of considerable value in rubber manufacturing. They are run through a machine which tears them to shreds, then through a sort of fanning-mill which blows away the bits of lining. Tiny pieces of iron may be present from nails or rivets; but these are easily removed by magnets. This "reclaimed" rubber is powdered and mixed with the new, and for some purposes the mixture answers very well. Imitation rubber has been made by heating oil of linseed, hemp, maize, etc., with sulphur; but no substitute for rubber is a success for all uses.

[Illustration: _Courtesy U. S. Tire Co._


Splitting Para biscuits, mixing the rubber, rolling the rubber fabric on cylinders, and building tires on the tire machines.]

There are many little conveniences made of rubber which we should greatly miss, such as the little tips put into pencil ends for erasing pencil marks. These are made by filling a mould with rubber. Rubber corks are made in much the same manner. Tips for the legs of chairs are made in a two-piece mould larger at the bottom than at the top, and with a plunger that nearly fits the small end. Often on chair tips and in the cup-shaped eraser that goes over the ends of some pencils you can see the "fin," as the glassworkers call it, where the two pieces of the mould did not exactly fit. Rubber cannot be melted and cast in moulds like iron, but it can be gently heated and softened, and then pressed into a mould. Rubber stamps are made in this way. The making of rubber heels and soles is now a large industry; hose for watering and for vacuum and Westinghouse brakes is made in increasing quantities. The making of rubber tires for automobiles and carriages is an important industry. The enormous and increasing use of electricity requires much use of rubber as an insulator. Rubber gloves will protect an electrical workman from shock and a surgeon from infection. Rubber beds and cushions filled with air are a great comfort in illness. Rubber has great and important uses; but we should perhaps miss quite as much the little comforts and conveniences which it has made possible.

Rubber and gutta-percha are not the same substance by any means. Both of them are made of the milky juice of trees, but of entirely different trees. The gutta-percha milk is collected in an absurdly wasteful manner, namely, by cutting down the trees and scraping up the juice. When this juice reaches the market, it is in large reddish lumps which look like cork and smell like cheese. It has to be cleaned, passed through a machine that tears it into bits, then between rollers before it is ready to be manufactured. It is not elastic like rubber; it may be stretched; but it will not snap back again as rubber does. It is a remarkably good nonconductor of electricity, and therefore it has been generally used to protect ocean cables, though recently rubber has been taking its place. It makes particularly excellent casts, for when it is warm it is not sticky, but softens so perfectly that it will show the tiniest indentation of a mould. It is the best kind of splint for a broken bone. If a boy breaks his arm, a surgeon can put a piece of gutta-percha into hot water, set the bone, bind on the softened gutta-percha for a splint, and in a few minutes it will be moulded to the exact shape of the arm, but so stiff as to keep the bone in place. Another good service which gutta-percha renders to the physician results from its willingness to dissolve in chloroform. If the skin is torn off, leaving a raw surface, this dissolved gutta-percha can be poured over it, and soon it is protected by an artificial skin which keeps the air from the raw flesh and gives the real skin an opportunity to grow again.

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