The Romance of Modern Chemistry

THE VALUE OF THE BY-PRODUCT ticularly important to get all the phosphorus removed from the metal, and this is best secured by adding quicklime to the molten pig. Any phosphorus which is present in the latter is oxidised by the blast of air, and is then in a condition to combine with the lime’ The slag, therefore, which is obtained at the end of the operation, contains phosphate of lime, and it is just the presence of this phosphate which makes basic slag valuable as a fertiliser. The greater part, say 1,500,000 tons, of the basic slag which is turned out of the steelworks of Europe is sold for this purpose. The only thing necessary in order that its fertilising power should be available is that it be finely ground. This is quite a straightforward operation, so that we have here an excellent example of the way in which the waste material of an industry is converted very simply into a valuable by-product. More striking than any of the cases yet quoted is the tale of the soda industry in Great Britain. Not once, but twice during its history, a waste product of the most disagreeable description has become a valuable source of income to the manufacturer. Refuse has been converted into riches, and one of the by-products has actually become the most important part of the output. Carbonate of soda is found in nature to a limited extent, but it is the artificial production which alone is of any importance. This goes back to about the time of the French Revolution, when a certain French- man, Leblanc by name, first showed how to turn common salt into carbonate of soda. Any one who seeks to produce soda on a large scale is bound to start with salt, for it is the compound of sodium of which there is the most plentiful supply in Nature. The process