[33] An ounce of eggs produces about forty thousand worms, and these, during the grub stage, require about fifteen hundred pounds of leaves, about one-half of which is actually consumed.
[34] Charles II. of England also forbade its use (1675) and attempted to close the coffee-houses that had sprung up in London, but in spite of the ban and the prohibitive tax laid upon it, the use of coffee became general. Similar efforts to close the coffee-houses in Constantinople failed.
[35] The full-grown leaf attains a length of from four to nine inches; those picked rarely exceed one-and-a-half inches in length.
[36] Brick tea consists of leaves moulded into bricks under heavy pressure. Refuse and stems are also thus prepared for the cheaper grades.
[37] The following are the chief rubber-producing trees: Siphonia elastica, or Hevea brasiliensis, Amazon forests, yields Pará rubber; Manihot Glaziovii, also a tapioca-producing shrub, Ceará province, Brazil, furnishes Ceará rubber; Castilloa elastica, Central American States, Nicaragua rubber; Ficus elastica, British India, and Urceola elastica, Borneo, Indian rubber. There are rubber-producing trees in Florida, but they have little commercial value at the present time. African rubber is taken from a variety of plants.
[38] The process of vulcanizing was made practicable during the ten years ending in 1850. It was invented and perfected by Goodyear in the United States and by Hancock in England; for ordinary purposes, where both strength and elasticity are required, about five per cent. of sulphur is added. The addition of about fifty per cent. changes the rubber to a hard black substance known as "ebonite," or "hard rubber."
[39] In 1823 a Scotchman, Mackintosh, applied the discovery, that rubber gum was soluble in benzine, to the water-proofing of the cloth that bears his name. This invention was about the first extensive commercial use to which rubber had been put.
[40] From the fact that most of the dwellings in the United States are built of wood, the United States is a very heavy consumer of turpentine.
[41] A slender strip of metallic lead was used instead of graphite in the first pencils made. The use of graphite did not become general until about 1850. The hardness of a pencil is regulated by mixing clay with the powdered graphite.
[42] These percentages are on the supposition that the ores are chemically pure; the percentage of metal actually obtained is somewhat less.