Catalysis or the Speeding-up of Chemical Reactions 39 



the acid otherwise. They made u&e of the great solubility of the 

 acid in water, and discharged it into neighbouring streams : but 

 the streams so polluted were the cause of the destruction of fish, 

 and in consequence this |)ractice also had to be abandoned. After 

 some study of the question it was found that if the hydrochloric 

 acid fumes were mixed with air, and passed over heated bricks 

 which had previously been moistened with a solution of cuprous 

 chloride, a reaction took place, and chlorine was produced. The 

 chlorine was absorbed by lime, yielding bleaching powder, for 

 which there was a brisk demand. Thus by the catalytic action of 

 cuprous chloride, a bye-product which had previously not only 

 been a loss but also a nuisance to the manufacturers, was trans- 

 formed into a valuable compound which proved a very welcome 

 source of revenue to the companies. 



The second bye-product in the process was a substance 

 known as ' black ash,' consisting largely of calcium sulphide. For 

 this there was no demand, and it was therefore tipped-up outside 

 the works. In course of time mountains of this waste material 

 had accumulated and proved a vexatious question to the manu- 

 facturers, not only on account of the space it occupied, but also 

 because of the offensive smell. It was found that the calcium 

 sulphide could be made to yield its sulphur in a very pure state, 

 and as this was a good marketable substance the question of the 

 profitable disposal of the black ash was settled. The calcium 

 sulphide is decomposed by carbonic acid gas, yielding calcium 

 carbonate (chalk) and sulphuretted hydrogen : the latter is con- 

 verted by the catalytic action of iron oxide into sulphur and 

 steam when a mixture of it and air is passed through a kiln 

 packed with iron oxide. Thus the discovery of suitable catalysts 

 gave a new lease of life to the Leblanc alkali process and enabled 

 it to compete successfully with newer rivals. 



Sulphuric Acid Manufacture. — In the further study of the 

 bearing of catalysis on manufacturing questions the difficulty is 

 not one of dearth of material, but is rather a question of making 

 a judicious selection that may prove both interesting and instruc- 



