SULPHURIC ACID.
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but sometimes they are made so large, that they are worth £1000 each.In this apparatus the acid is deprived of a part of its water and somesulphurous acid, and when it has attained a sufficient degree of concen-tration, it is drawn off by means of a platinum syphon into carboys.
The theory of the process is the following:—When sulphurous andnitric acids come in contact, the first fees, the second gam s, oxygen,by which sulphuric and nitrous acids are formed. Dry nitrous acidand sulphurous acid gases undergo no change when mixed; but, if alittle moisture be admitted, re-action takes place, and a crystalline com-pound, of sulphuric acid, hyponitrous acid, and water, is formed. This,falling into water, is immediately decomposed: sulphuric acid is dis-solved, and the hyponitrous acid is resolved into nitrous acid and binoxideof nitrogen, which escape with effervescence in a gaseous form. The nitrousacid thus disengaged, with that produced by the union of the binoxidewith oxygen of the atmosphere, becoming mixed with more sulphurousacid and water, gives rise to a fresh portion of the crystalline compound.One part of the nitrous acid is converted by the water present into nitricacid and binoxide of nitrogen ; while another portion loses the whole ofits oxygen, by which a little nitrogen gas is disengaged. In oil of vitriolmanufactories the crystalline compound is rarely formed, owing to theexcess of aqueous vapour present. Sometimes, however, it is deposited inthe pipe which conveys away the superfluous vapour, as in the instancementioned by Dr. Henry (Ann. Phil. vol. xi. new series, p. 368). Forfurther information respecting the manufacture of sulphuric acid, see thepapers of Gaultier de Claubry, in Ann. de Chim. xlv. 284 ; and Did. deI'lndust. tom. i. pp. 108, et seq).
The old method of manufacturing oil of vitriol, and, indeed, one stillfollowed in some places, consists in burning a mixture of eight parts ofsulphur and one part of nitrate of potash (or nitrate of soda) on iron orleaden plates, either within the leaden chamber or in a furnace on theoutside of it (Parkes’s Chemical Essays, vol. i. 465). Fig. 51 is the ground
Iron pyrites (bisulphuret of iron) is
In this process the greater part oj'the sulphurcombines with oxygen ofthe air to form sulphurous acid: buta portion abstracts oxygen from thenitric acid of the nitrate, and therebybecomes sulphuric acid, which, withthe potash of the nitre, forms sulphateof potash. Binoxide of nitrogen isevolved by the decomposed nitricacid, and this, combinin g with oxy genof the air, becomes nitrous acid. Themutual action of sulphurous andnitrous acid gases has been beforeexplained.
At Goslar,Nordhausen , and otherparts of Saxony , sulphuric acid ismade thus:—Crystallized sulphate of iron is calcined, by which the greaterportion of its water of crystallization is expelled. It is then distilled inearthen vessels, by which fuming sulphuric acid is procured, while sesqui-
plan of a manufactory of this kind,sometimes substituted for sulphur.
Fig. 52.
Plan of a Sulphuric Acid Manufactory.