Page:Popular Science Monthly Volume 23.djvu/830

810 winter the taps and spouts and water-pipes are covered with this slag-wool, it prevents the freezing of the water and the bursting of the pipes and joints. This slag-wool is also used now by gardeners to cover plants and protect them from the effects of sudden changes of temperature.

In view of the general usefulness of slag, when converted into the various articles described, it is to be hoped, in the interests of commerce and progress, that the practice of its utilization may become more and more extended. Doubtless, human progress will show that what is now the veriest waste will, in the course of time, assume a condition of value. Thus will art be made to approximate to nature, in that it will know no waste.

There are one or two other mineral substances, formerly neglected, which have of late years been applied to very extensive important uses. One of these is asbestos. This was long considered a mere curiosity for making small fire-proof articles. It is the only flexible fibrous mineral substance that is perfectly indestructible by fire or acids, notwithstanding it consists of fibers as fine as the finest linen. Now it is scarcely possible to enumerate all the uses to which it is applied. Among others are, as a roofing material, cement, paint, fireproof coating for inside of factories, theatres, etc., in danger of ignition, felting for steam-pipes, boilers, lining for floors, roofs, etc.

A prominent and peculiar feature in the landscape of the coal mining regions is the enormous heaps of black and apparently useless material collected near the outlet of each mine. As the quantity of small waste coal in the United Kingdom has been estimated at 28,000,000 tons per annum, the utilization of this refuse is a matter of national importance in more senses than one. It is now, in many districts, consolidated into blocks, and, besides what is used at home, 412,310 tons of this patent manufactured fuel were exported last year.

In several foreign countries, the pitch from coal-tar is combined with coal-dust, and pressed into the form of bricks, and an excellent fuel is thus produced, which, it is said, will generate a greater amount of heat than can be obtained from the same quantity of any other combustible material employed for utility or comfort, while, at the same time, it can be stored more compactly and in better shape than either wood or coal. Some 40,000,000 tons of valueless coal-dust, lying in the vicinity of the coal-mines and depots of Pennsylvania, have been thus gradually utilized. In some American factories they have found it cheaper and more advantageous to burn only coal-dust or pea coal. A furnace or grate bar has been specially devised for the purpose of burning this kind of fuel, and there is no doubt, with its increasing uses, but that other convenient devices will be supplied for making it of more practical benefit. The utilization of this waste in the coal-regions of the United States is now a decided success. The American Fuel Company, Pennsylvania, works up large quantities of