the most useful substances in the arts and sciences—nay, to be an absolute necessity of civilisation.
It is, at the same time, very remarkable that, for upwards of sixty years, india-rubber never advanced beyond the hands of the drawing-master, and that, during that long period, all its virtues were supposed to consist in its power of correcting school-girls’ drawings. How many substances are there still before the world in a like condition of embryo?—what is to be the splendid future of gutta-percha, aluminum, and the other scores of new substances that are beginning to “crop” up around us?
It would seem as though it were destined for the rubber plant to play a great part in the world, as it is found in great abundance in all parts of the globe, within tropical latitudes; and, like the palm, it is probably destined to do the missionary work of civilisation far more effectually than any of our societies constituted for that purpose, as the pursuit of these two valuable products will lead organised bands of European traders deeper and deeper into the recesses of the tropical wilderness—where the solitary missionary could not hope to make any permanent lodgement. The best kinds of caoutchouc are the Para and the bottle india-rubber, the latter is familiar enough to the reader: but perhaps it is not so well known that what is termed caoutchouc is the milk sap of trees, and that this juice is to be found in many other trees besides the rubber tree; indeed, there seems to be little doubt that we may draw upon a large portion of the tropical vegetable world for this valuable material. The india-rubber as imported takes the form of bottles, and there is a kind known as negro-head, possibly because when cut open it presents an appearance somewhat like that of a human brain, with its numerous convolutions. The first process we witnessed at the Messrs. Silver’s was the softening of these bottles and “negro brains,” if we may use the term, in a large tank, filled with warm water. The rubber is macerated here for some hours, for the purpose of softening and cleansing it—the process it undergoes in the school-boy’s mouth. When it has been long enough in the water, it is taken to the masticating machine, which is a kind of calendering apparatus, heated by steam, and operating upon the lumps of rubber as the boy’s grinders do. You see the big lumps drawn in between the smooth cylinders, apparently the most obstinate, indigestible, unmanageable stuff in the world, and after a while it issues from the other side in the form of so many “brown bread towels,” or those coarse-looking, oatmeal coloured rubbing cloths that are a necessary appendage to every sponging-bath. The transformation from the dirty-looking lumps of rubber to these little towels, about eight inches wide and three feet long, is the oddest thing possible. As they emerge, they are folded up and placed on shelves, just as we see them in baths and wash-houses. Twenty-four hours’ exposure to the air changes their oatmeal colour to a very dark brown. This is the first stage through which all the different preparations of india-rubber go—its cleansing process. The reader will possibly remember that india-rubber presents itself under different aspects, either as pure india-rubber, such as tobacco-pouches, &c., are made of, or as whitish-looking india-rubber, which we are familiar with in the form of macintosh cloaks. The vulcanised india-rubber has a somewhat similar aspect—a clay-like colour, as far removed as possible from the rubber as we see it in the bottle. Pure india-rubber is manufactured in a very simple manner. A number of the brown bread towels are taken to the masticator, a machine composed of two powerful steel rollers, revolving with unequal velocities, and heated by steam. The “towels” disappear in this powerful mangle, and the act of masticating begins. As towel after towel disappears, the rubber is worked into a huge bolster, which is masticated over and over again, until it assumes the form of sticky pulp—“bladder pop,” in fact, on a large scale. The bolster is now taken from the machine, and placed in an hydraulic press, one foot wide, nine inches deep, and six feet long. Here it remains for two days, under a pressure of fifty tons, and comes out a solid block of homogeneous india-rubber, big enough for a Titanic drawing-master. It has now to be cut into sheets. This is done by placing it in a machine fitted with a cutter, which cuts with a quick lateral or saw-like motion. The block is pushed forward against this cutter, and the thickness of the sheet can be regulated to the hundred and twentieth of an inch; indeed, sheets of that tenuity are sometimes made. It is a pretty sight to watch the thin film of rubber being detached in this way, with an unerring accuracy.
The most important application of india-rubber in this form, is its use as an insulator for telegraphic purposes. Hitherto, gutta-percha has been almost universally employed—for deep-sea cables especially—but there can be little doubt that india-rubber is a far more durable material, and it is slowly coming into use, notwithstanding the opposition of the manufacturers who have embarked large capital in the collection and working of gutta-percha. It is one of the most interesting sights in the manufactory to see the machinery envelope the telegraphic wires with its non-conducting rubber sheathing. This is done by winding round them spirally thin bands of rubber, by machinery driven by steam-power. Thirty or forty spindles for this purpose are seen revolving in a large room, and hundreds of miles of wire are thus covered in the course of the week. The covered wire is subjected afterwards to heat, which fuses the laps of the covering riband of rubber together, and thus makes it impermeable to the entrance of water, and effectually prevents the escape of electricity.
The process of manufacturing soft india-rubber is more elaborate. What is termed Spread sheet india-rubber, or that kind of which waterproof garments are manufactured, is made by masticating, and mixing sulphur in the proportion of two ounces to a pound of the rubber, and then dissolving it to the consistency of dough by the admixture of naphtha. When in this soft state it is passed through finely-adjusted rollers and spread out into thin sheets; these as they emerge from the