. The Pharmaceutical era. e air sulfurous acid gradually com-bines with oxygen to form sulfuric acid, so that nearlyall of its solutions contain more or less of the latter com-pound. The salts of sulfurous acid, the sulfites, are an impor-tant class of compounds, useful both in the arts and iamedicine, their chief value lying in their ability to re-lease sulfur dioxid when treated with an acid. This re-action also serves to detect them in the process of analy-sis. —Thisisa colorless, heavy, oily liquidformerly called oil of vitriol, because first obtained bythe distillation
. The Pharmaceutical era. e air sulfurous acid gradually com-bines with oxygen to form sulfuric acid, so that nearlyall of its solutions contain more or less of the latter com-pound. The salts of sulfurous acid, the sulfites, are an impor-tant class of compounds, useful both in the arts and iamedicine, their chief value lying in their ability to re-lease sulfur dioxid when treated with an acid. This re-action also serves to detect them in the process of analy-sis. —Thisisa colorless, heavy, oily liquidformerly called oil of vitriol, because first obtained bythe distillation of green vitriol. The Achlum S^ilphuricum of the Pharmacopoeia con-tains per cent, of the absolute acid, and has a spe-cific gravity of It can be prepared like sulfurousacid, by dissolving the corresponding anhydrid in ,+ H,0 = H, On the commercial scale it is manufactured by passingsinto large leaden chambers, sulfur dioxid, obtained byburning sulfur, steam, air, and nitric acid, or certain ox-. Fig. 27.—Manufacture of Sulfuric Acid. ids of nitrogen. (Fig. 27.) The sulfur dioxid cannotreadily take up oxygen from the air, but can easily take November IS, 1897.] THE PHARMACEUTICAL ERA. 751 it from till nitric acid or the nitrogen oxids which arepresent. Tlio latter in turn take up fresh oxytren fromthe air, and thus act as carriers of oxygen from the airto the sulfur. The completed reaction may be represent-ed by the following equation, though it is quite certainthat intermediate reactions occur: 3H,S03 + 2HNO3 = 3H,S0, + 2NO + II,0. The weak acid of the chambers is first concentrated inleaden and then in platinum vessels, and finally purifiedby distillation from platinum stills. Sulfuric acid is probably the most important acidknown. It is used in the preparation of many otheracids, and in a large number of other chemical opera-tions. Enormous quantities of it are consumed yearly. The concentrated acid has a great affinity for water,mixing with it w
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