8io THE POPULAR SCIENCE MONTHLY. 



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 com- 

 merce 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, fire- 

 proof coating for inside of factories, theatres, etc., in danger of igni- 

 tion, 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 pur- 

 pose 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 



