The Romance of Modern Chemistry

THE VALUE OF THE BY-PRODUCT we might suppose that there would be contentment all round, among the public as well as among the manufac- turers. But this was not so, and the cause of trouble was the second stage of the Leblanc soda process. We have been so occupied in following up the history of the waste hydrochloric acid that we have yet to learn the fate of the salt cake which is produced at the same time. In the second stage of the Leblanc process the salt cake is mixed with limestone and coal dust, and heated in a furnace. The chemical changes which take place in this furnace are somewhat complicated, but the net result is a product known as “ black ash,” consisting chiefly of carbonate of soda and sulphide of lime. With the help of water, the soda is extracted from the black ash, the portion which is insoluble being termed “ alkali waste.1’ This objectionable refuse contains both the calcium from the limestone and the sulphur originally used in the manufacture of the sulphuric acid for the first stage. Of these, the sulphur is especially valuable, but for many long years no satisfactory method could be devised for recovering it from the waste, which was simply thrown away. The accumulation of this waste material in the neigh- bourhood of alkali works led to much unpleasantness. Even when it was stamped down and covered over with a layer of cinders, moisture and air gradually got at the waste, with the result that sulphuretted hydrogen gas was given off into the atmosphere. Apart from the abominable odour, such accumulations are themselves an eyesore, and their magnitude is such that one can appre- ciate the importance of the soda industry from a mere glance at these rubbish-heaps. Those in the neighbour- hood of Widnes alone, to which reference was made in 277