Thomas Bolas

“ The commercial value of the various qualities of rubber may be estimated, to a certain extent, by noting the loss which the samples undergo during the operation of washing, and also by noticing how far the various samples are softened by a long-continued gentle heat. Here are some samples which have been heated for some hours in this water-oven; you will notice that the African tongue has become almost as soft as treacle, while the Para rubber still retains its form and much of its consistency.
Caoutchouc is nearly colorless, and when in thin leaves tolerably transparent. ”

“ The elasticity of caoutchouc may be enormously increased by vulcanization.
As regards the stretching of India-rubber, there is a point at which it requires a greatly increased force to stretch it, and at this point it seems to become fibrous in texture, as you may perceive by examining this extended sample by the aid of a magnifying-lens. India-rubber has valuable electrical properties, as you are no doubt aware, it being an admirable insulator, and having a great tendency to become electrical by friction. ”

“ The treatment of the juice of the India-rubber trees is often of such a nature as to greatly deteriorate the caoutchouc obtained; a considerable proportion being thus changed from the fibrous to the viscous condition. This kind of injury to the caoutchouc can be obviated by coagulating the milky juice, and carefully drying the clot after it has been subjected to pressure. For experimental purposes, alcohol may be employed as a coagulating agent ”

“ The milky juice of the Para rubber trees, of which you see a specimen before you, has approximately the following composition:
As a rubber-producing tree, the Ficus elastica stands next in importance of the heveas. The Ficus elastica grows abundantly in India and the East Indian Islands, one district in Assam, thirty miles long by eight miles wide, being said to contain 43,000 trees, many of them attaining a height of a hundred feet. This tree also grows freely in Madagascar, and it is well known to us as a greenhouse plant. ”

“ The residues of juice left in the various vessels employed, the scrapings of the incisions, together with other materials, which the ingenious native thinks he can shuffle off on the unsuspecting merchant as caoutchouc, are made into balls, and sold as "negro-head." The negro-head rubber is frequently made into crude representations of animals, and there are several such works of native art on the table—as, for example, this specimen, which will pass about equally well for a horse, a pig, or a crocodile. ”

“ Caoutchouc may be utterly ruined by the use of impure solvents, and those experimenting with India-rubber solutions should, in cases where it is desirable to regenerate the caoutchouc by allowing the solvent to evaporate, take the utmost care not to employ any solvents which contain fatty or greasy matter. ”

“ In each case you see that the caoutchouc is restored to its original condition. In the case of the stretching it is very likely that the effect is due to the heat evolved during that operation. It is easy to illustrate the fact that heat is produced when India-rubber is subjected to tension. Here are some strips of India-rubber, arranged side by side on a board. ”

“ At the present time, caoutchouc holds such an important position with regard to the economy of modern arts and manufactures, that, were it suddenly to be withdrawn from circulation, many minor industries would in consequence cease to exist ”

“ It becomes, as you see, rigid and stiff, but its original pliability may be restored, either by warming, or by applying sufficient tensile strain to it, to extend it to three or four times its length. ”