Page:Popular Science Monthly Volume 85.djvu/454

450 the conditions for vulcanizing and otherwise treating Para rubber are better known and rubber manufacturers will probably agree with the opinion expressed to me by one of them that plantation rubber is not so easily worked. Para rubber is said to be harder and "nervier" in the mixing rolls and is more consistent in quality. What causes the difference is unknown; whether the immaturity of the plantation trees, or the method of curing or some other factors. The difference is exhibited not only in the ways indicated, but also by the action of some chemical reagents. In a series of experiments, the part of Para rubber soluble in petroleum ether was in one sample 51 per cent., in another 57 per cent., while of Ceylon biscuit 58 per cent, and 68 per cent, were soluble, and of Malayan crepe 72 per cent, and 86 per cent. The part dissolved from the Para rubber was much more viscous than that from the other kinds.

The price of plantation rubber in the London market is lower than that of Para rubber, but this is probably due, at least partly, to the method of sale by auction. According to The Economist, during the first eight months of 1913, Para averaged 3s. 10d. while plantation rubber averaged 3s. 5d. and, curiously enough, when plantation rubber dropped in September to 2s. a pound, Para was 3s. 7d.

Though up to the present plantation rubber is not equal in quality to the best Para rubber, it will be remembered that a considerable quantity of the rubber from the Amazon district itself is not of the highest grade. One quarter or more is of inferior quality. The price in general has dropped till it leaves little margin above the cost of production. While the export from the Amazon district has increased little, if any, since 1909, being in the neighborhood of 42,000 tons, plantation rubber, which in 1909 was 4,000, amounted in 1912 to 30,000 tons. The total rubber consumption in 1912 was about 108,000 tons, part of it being wild rubber from Mexico and various places in Africa, part being old rubber reclaimed. In the season 1912-13, according to the IT. S. Consular Reports, the Amazon district exported 2,200 tons more than in the previous season, but the same reports predicted a decrease in the season 1913-14 and, according to the Journal of Commerce, during July, August and September, the first three months of the 1913-14 season, the export was 7,161 tons as compared with 8,553 tons of the year before. The statement is made in the Consular Reports that this year for the first time other countries will produce a greater amount of plantation rubber than the Amazon Valley of wild rubber.

Mr. Akers, a British rubber expert, estimates that in 1916 plantations could yield 173,000 tons and in 1919, about 300,000 tons. He also estimates that if rubber falls to two shillings a pound 150,000 tons or perhaps 200,000 tons might be consumed for the present uses, but unless new uses not now apparent are discovered the supply will much exceed the demand.