When you pick a dandelion or a milkweed, a white sticky "milk" oozes out; and this looks just like the juice of the various sorts of trees, shrubs, and vines from which India rubber is made. The "rubber plant" which has been such a favorite in houses is one of these; in India it becomes a large tree which has the peculiar habit of dropping down from its branches "bush-ropes," as they are called. These take root and become stout trunks. There is literally a "rubber belt" around the world, for nearly all rubber comes from the countries lying between the Tropic of Cancer and the Tropic of Capricorn. More than half of all that is brought to market is produced in the valley of the Amazon River; and some of this "Para rubber," as it is called, from the seaport whence it is shipped, is the best in the world.

The juice or latex flows best about sunrise, and so the natives who collect it have to be early risers. They make little cuts in the bark of the tree, stick on with a bit of clay a tiny cup underneath each cut, and move on through the forest to the next tree. Sometimes they make narrow V-shaped cuts in the bark, one above another, but all coming into a perpendicular channel leading to the foot of the [7] tree. Later in the day the collectors empty the cups into great jugs and carry them to the camp.

When the rubber juice reaches the camp, it is poured into a great bowl. The men build a fire of sticks, and always add a great many palm nuts, which are oily and make a good deal of smoke. Over the fire they place an earthen jar shaped like a cone, but without top or bottom. Now work begins. It is fortunate that it can be done in the open air, and that the man can sit on the windward side, for the smoke rises through the smaller hole thick and black and suffocating. The man takes a stick shaped like a paddle, dips it into the bowl, and holds it in the smoke and heat, turning it rapidly over and over till the water is nearly dried out of the rubber and it is no longer milky, but dark-colored. Then he dips this paddle in again and again. It grows heavier at each dipping, but he keeps on till he has five or six pounds of rubber. With a wet knife he cuts this off, making what are called "biscuits." After many years of this sort of work, some one found that by resting one end of a pole in a crotched stick and holding the other in his hand, a man could make a much larger biscuit.

For a long time people thought that rubber trees could not be cultivated. One difficulty in taking them away from their original home to plant is that the seeds are so rich in oil as to become rancid unusually soon. At length, however, a consignment of them was packed in openwork baskets between layers of dried wild banana leaves and slung up on deck in openwork crates so as to have plenty of air. By this means seven thousand healthy little plants were soon growing in England, and from there were carried to Ceylon and the East.

On the rubber plantations collecting juice from trees standing near together and in open ground is an altogether different matter from cutting a narrow path and forcing one's way through a South American or African jungle. The bark of the trees is cut in herringbone fashion. The collector simply slices a thin piece off the bark and at once milk begins to ooze out.

On the great plantations of the East the rubber is collected chiefly by Chinese and Indians. They are carefully taught just how to tap the trees. They begin four or five feet from the ground, and work down, cutting the thinnest possible slice at each visit. When they have almost reached the ground, they begin on the opposite side of the trunk; and by the time they have reached the ground on that side the bark on the first side has renewed itself. The latex is strained and mixed with some acid, usually acetic, in order to coagulate or thicken it. It is then run between rollers, hung in a drying house, and generally in a smokehouse.

The rubber arrives at the factory in bales or cases. First of all it must be thoroughly washed in order to get rid of sand or bits of leaves and wood. A machine called a "washer" does this work. It forces the rubber between grooved rolls which break it up; and as this is done under a spray of water, the rubber is much cleaner when it comes out. Another machine makes it still cleaner and forms it into long sheets about two feet wide.

Having thoroughly wet the rubber, the next step is to dry it thoroughly. The old way was to hang it up for several weeks. The new way is to cut it into strips, lay it upon steel trays, and place it in a vacuum dryer. This is kept hot, and whatever moisture is in the rubber is either evaporated or sucked out by a vacuum pump. It now passes through another machine much like the washer, and is formed into sheets. The square threads from which elastic webbing is made may be cut from these sheets, though sometimes the sheet is wound on an iron drum, vulcanized by being put into hot water, lightly varnished with shellac to stiffen it, then wound on a wooden cylinder, and cut into square threads. Boiling these in caustic soda removes the shellac. To make round threads, softened rubber is forced through a die. Rubber bands are made by cementing a sheet of rubber into a tube and then cutting them off at whatever width may be desired. Toy balloons are made of such rubber. Two pieces are stamped out and joined by a particularly noisy machine, and then the balloon is blown out by compressed air.

Early in the nineteenth century it was known that rubber would keep out water, but it was sticky and unmanageable. After a while a Scotch chemist named McIntosh succeeded in dissolving rubber in naphtha and spreading it between two thicknesses of cloth. That is why his name is given to raincoats made in this way. Overshoes, too, were made of pure rubber poured over clay lasts which were broken after the rubber had dried. These overshoes were waterproof,—there was no denying that; but they were heavy and clumsy and shapeless. When they were taken off, they did not stand up, but promptly fell over. In hot weather they became so sticky that they had to be kept in the cellar; and in winter they became stiff and inelastic, but they never wore out. How to get rid of the undesirable qualities and not lose the desirable ones was the question. It was found out that if sulphur was mixed with rubber, the disagreeable stickiness would vanish; but the rubbers continued to melt and to freeze by turns until an American named Charles Goodyear discovered that if rubber mixed with sulphur was exposed to about 300°F. of heat for a number of hours, the rubber would remain elastic, but would not be sticky and would no longer be affected by heat or cold. This is why you often see the name Goodyear on the bottom of rubbers.

Rubber overshoes were improved at once. As they now are made, the rubber is mixed with sulphur, whiting, litharge, and several other substances. An honest firm will add only those materials that will be of service in making the rubber more easy to mould or will improve it in some way. Unfortunately, substances are often added, not for this purpose, but to increase the weight and apparent value of the articles. That is why some rubber overshoes, for instance, wear out so much faster than others.

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.

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.