Note 45 — Chapter XX · SULPHUR, SELENIUM, AND TELLURIUM

The removal of the water, or concentration to almost the real acid, H2SO4, is effected for two reasons: in the first place to avoid the expense of transit (it is cheaper to remove the water than to pay for its transit), and in the second place because many processes—for instance, the refining of petroleum—require a strong acid free from an excess of water, the weak acid having no action. When in the manufacture of chamber acid, both the Gay-Lussac tower (cold, situated at the end of the chambers) and the Glover tower (hot, situated at the beginning of the plant, between the chambers and ovens for the production of SO2) are employed, a mixture of nitrose (i.e. the product of the Gay-Lussac tower) and chamber acid containing about 60 p.c. H2SO4, is poured into the Glover tower, where under the action of the hot furnace gases containing SO2, and the water held in the chamber acid (1) N2O3 is evolved from the nitrose; (2) water is expelled from the chamber acid; (3) a portion of the SO2 is converted into H2SO4; and (4) the furnace gases are cooled. Thus, amongst other things, the Glover tower facilitates the concentration of the chamber acid (removal of H2O), but the product generally contains many impurities.