“ A vitreous material resembling wool, made by subjecting slag, when in a molten condition, to a strong blast. It was originally made in Wales in 1840, but the process was found injurious to the workmen, and so the manufacture was abandoned until about thirty years later, when it was taken up in Germany. As now made, a jet of steam is made to strike upon a flowing mass of molten slag as it falls from the spout into the slag-carriers. The steam scatters the slag into globules, and as each globule leaves the molten stream it turns into a fine thread. ”

“ As it is fireproof and insect-proof, it has been used generally by architects and builders as a packing for walls. It also possesses value as a non-conductor of sound and is therefore valuable in school buildings and music halls. ”