It is a matter of common knowledge among chemists that sulphuric acid is made by two processes, the contact proccss and the lead-chamber proccss, which arc now about equally important.
In the contact proccss sulphur trioxidc is made by the catalytic oxidation of sulphur dioxide (the name of the proccss refers to the fact that reaction occurs on contact of die gases with the solid catalyst). The catalyst formerly used was finely divided platinum; it has now been largely replaced by vanadium pentoxide, V:05. The gas containing sulphur trioxidc is then bubbled through sulphuric acid, which absorbs the sulphur trioxidc. Water is added at the proper rate, and 98% acid is drawn oft.
In the lcad-chambcr proccss oxygen, sulphur dioxide, nitric oxide, and a small amount of water vapour arc introduced into a large lead-lined chambcr. White crystals of nitrosulphuric acid, NOHSO4 (to put it in another way, sulphuric acid in which one hydrogen ion is replaced by the nitronium ion, :Nsa O*:), arc fonncd. When steam is introduced the crystals react to form drops of sulphuric acid, liberating oxides of nitrogen. In cffcct, the oxides of nitrogen serve to catalyze the oxidation of sulphur dioxide by oxygen. The reactions that occur may be summarized as
2SO:+ NO + NO:+ 0:+ H2O -> 2NOHSO4;
2N0HS04+ H20 2H:S04+ NO + N0:.
The oxides of nitrogen, NO and NO*, diat take part in the first reaction, arc released by the second reaction, and can serve over and over again.
It should be pointed out in conclusion that however widespread these processes may be, they arc by no means die only ways of the manufacture of sulphuric acid.
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