The Romance of Modern Chemistry

THE VALUE OF THE BY-PRODUCT It is perhaps too much to hope that such an enormous mass of waste material will ever be entirely devoted to useful ends instead of disfiguring the landscape and covering up the fertile soil, but recent work has un- doubtedly led to encouraging results in the utilisation of slag. Much of it is employed in road-making and in reclaiming waste land, but in addition there is now made a very large quantity of slag cement, for which purpose the finely powdered slag is mixed with lime. Another purpose to which considerable quantities of slag are devoted is the making of “ slag wool.” This curious product is somewhat similar to “glass wool,” the name in each case indicating a resemblance to cotton wool. When a jet of steam is directed against molten slag, little globules of the liquid material are blown off, each with a long, thin tail or filament By mechanical means the filaments are separated from the globules, and slag wool consists simply of masses of the filaments. It is a non-conducting, non-inflammable material, and as such is usefully employed in covering steam-pipes and boilers. In virtue also of its non-conducting pro- perties, it is used to coat refrigerating plant It is very curious that while there has been such difficulty in utilising blast-furnace slag, there is another kind of slag, turned out from steelworks, which has found a ready application. If the reader considers for a moment how this basic slag, as it is called, is obtained, he will understand why it is a more valuable by-product than blast-furnace slag. Steel is obtained by blowing air into molten pig-iron ; the impurities in the latter are thereby oxidised, and the purified metal is then supplied with the requisite quantity of carbon to convert it into steeL It is par- 272