Page:Popular Science Monthly Volume 16.djvu/110

 of gas-making. To begin with: the coal which yields most gas is what is termed "cannel" coal, and is now-worth from twenty-five to thirty shillings a ton or more; whereas fifty years ago, before the introduction of gas, it was looked upon as almost-worthless. In distilling coal for gas, a liquor is produced which for a long time was so great an inconvenience to the gas companies that they actually paid for permission to drain it into the common sewers, as the the simplest way of getting rid of it. This gas-liquor contains salts of ammonia, together with naphtha and tar; and the tar is now made by repeated distillation to yield pitch, benzole, creosote, carbolic acid, the substance known as paraffine, and aniline. It seems strange now that these valuable products should ever have been thrown away as useless; still stranger is it to learn that-we derive from one of these-waste substances the-whole series of beautiful colors called aniline dyes. Naphthaline is another residuary product, by a novel application of which it is said that the light-giving properties of gas may be enhanced fourfold, at a very trifling cost. But the uses to which the waste liquor of the gas-works may be put are not yet exhausted; for not only is it turned to account itself, but combined with the slaty shales found among the coal, which were also at one time a source of perpetual annoyance, it yields alum—used in the manufacture of paper and preparation of leather; copper as or green vitriol (sulphate of iron), used in dyeing, tanning, and the manufacture of ink and Prussian blue; and sulphuric acid.

Rags are now recognized as such a valuable commodity that in some countries their export is forbidden by government; nevertheless, from one source or another the paper-makers of England alone import annually some eighteen or twenty thousand tons of linen and cotton rags, and collect large quantities at home. These rags are of very varying degrees of cleanliness, as may be imagined; some of the English ones require no bleaching at all, while those of Italy bear away the palm for dirt. Old sails are made into the paper used for banknotes, so it is said, and old ropes reappear as brown paper; but many other things besides flax, hemp, and cotton are now used in the manufacture, and paper is made and remade over and over again. Not a scrap of paper need be wasted, for there are plenty of persons ready to buy it; and, if not good enough for remanufacture as paper, it can always be converted into papier-mâché, no matter what its color or quality. Cuttings of paper severed by bookbinders, pasteboard-makers, envelope-cutters, pocket-book-makers, and paper-hangers are readily bought up; and so too are tons-weight of old ledgers and account books by the papier-mâché manufacturer, together-with old letters and any other paper-rubbish, giving a pledge that all shall be promptly consigned to destruction in his large vat; and out of this heterogeneous assemblage he produces a substance so hard and firm and durable that it has been suggested as suitable for making soldiers' huts and even ships. It is already put to a variety of uses, and is employed