3854. Sulphuric Acid

3854. Sulphuric Acid. This is a colorless, odorless acid, and highly corrosive liquid, formed by the union of 1 equivalent of sulphur and 3 of oxygen. It is immediately colored by contact with organic matter. It attracts water so rapidly from the atmosphere, when freely exposed to it, as to absorb 1/3 its weight in 24 hours; and, under continued exposure, will absorb 6 times its weight.

When 4 parts water arc suddenly mixed with

1 part sulphuric acid, the temperature of the mixture rises to about 300° Fahr. Whilst 4 parts pounded ice mixed with 1 part acid, sinks the thermometer to some degrees below zero. Sulphuric acid boils and distills over at 620° Fahr., and freezes at about 20° below zero. The salts formed by the union* of sulphuric acid with a base are called sulphates.

3855. To Obtain Commercial Sulphuric Acid

3855.      To Obtain Commercial Sulphuric Acid. This is commonly called oil of vitriol, and has a specific gravity not less than 1.840, nor more than 1.845. It was first obtained by the distillation of green vitriol (sulphate of iron), but it is now made by bringing the fumes of sulphurous acid (see No. 3865 (To Obtain Sulphurous Acid)) into contact with those evolved from a mixture of nitre and oil of vitriol, so that the former becomes oxidized at the expense of the latter. This process is conducted in a series of leaden chambers, having a little water on the floor, to absorb the acid, and so arranged as to prevent the loss of gas. As soon as the water is found to have acquired a specific gravity of 1.350 to 1.450, it is drawn off, and concentrated (see No. 8 (Concentration)) in leaden boilers to a density of 1.G59 to 1.700; after which it is further concentrated in green glass or platinum retorts until the specific gravity reaches 1.842 to 1.844. "When cold, the clear acid is put into carboys (large globular bottles of green glass) packed securely with straw in strong wooden cases, the neck being left exposed for convenience in obtaining the acid without unpacking.

3856. Anhydrous Sulphuric Acid

3856.     Anhydrous Sulphuric Acid. Anhydrous or dry sulphuric acid is obtained by heating Nordhausen acid (see No. 3858 (Nordhausen Sulphuric Acid)) in a glass retort connected with a well-cooled receiver.

It is also prepared in the following manner:

2 parts strongest oil of vitriol are gradually added to 3 parts anhydrous phosphoric acid, contained in retort surrounded by a freezing mixture; when the compound has become brown, the retort is removed from the freezing bath and connected with a receiver which takes its place in the freezing mixture; a gentle heat is applied to the retort, when white vapors pass over and condense in the receiver under the form of beautiful silky crystals. The product equals in weight that of the phosphorus originally employed. The addition of a few drops of water to these crystals produces a dangerous explosion. They deliquesce rapidly and fume in the air; introduced into water, they hiss like red-hot iron. They melt at 66° Fahr., and boil at about 1050°, and do not redden dry litmus paper.