The Romance of Modern Chemistry

THE VALUE OF THE BY-PRODUCT It is quite easy to carry out the fermentation in closed vessels provided only with an outlet for the carbon dioxide, and by this method the gas could be collected and condensed to the liquid form in steel bottles; in this shape carbon dioxide is a marketable commodity. Such a conversion of the chief waste pro- duct of the brewing industry into a useful by-product has actually been carried out, and the carbon dioxide so obtained has found application in refrigeration and in the preparation of aerated waters. Nowadays, how- ever, the attempt to recover the carbon dioxide as a by-product is very seldom made, because, from the com- mercial point of view, it is not worth while. A waste product which is more tangible but less easy to deal with than carbon dioxide is blast-furnace slag. From what was said in a previous chapter, the reader will understand that iron-smelting consists essentially in heating together crude iron oxide, carbon in the form of coke, and a flux, such as lime, to remove the earthy material from the ore in a fluid form. At the end of the operation two things are obtained, namely, pig-iron and slag, the latter being simply the flux + the earthy material from the iron ore. It is mn out of the blast furnace in a molten condition and is a sort of cross between glass and cinders. This unpromising material is turned out in Great Britain at the rate of nearly twenty million tons annually, and the mere re- moval of this refuse from the foundry involves the smelters in very considerable expense. In some cases it is taken out and shot into the maw of the all-de- vouring sea. In other cases, as in the Black Country, it is allowed to accumulate in huge, unsightly mounds —veritable rubbish-heaps of modern civilisation. 271