The lead chamber process produces what is called chamber sulphuric acid very cheaply. Although this is only a 60-70 per cent. solution and very impure, nevertheless, it is quite good enough for the heavy chemical trade, particularly for the first stage of the Leblanc soda process, and for making superphosphate. These two industries alone consume many thousands of tons of this sulphuric acid every year. Probably for some years to come the two processes will continue to exist side by side, but it may be doubted whether new works will now be installed to make sulphuric acid by the lead chamber process.
Properties of Sulphuric Acid. The pure non-fuming acid is a colourless oily liquid whose density is 1·84. It mixes with water in all proportions, yielding dilute sulphuric acid, and it also dissolves sulphur trioxide, yielding the fuming acid.
The mixing of sulphuric acid and water is accompanied by an evolution of heat and by contraction in volume. It is an operation which must be carried out with great care, the acid being always poured into the water, otherwise the water floats on the heavier acid, and so much heat is developed at the surface of separation that some of the water will be suddenly converted into steam, and this, escaping from the liquid with explosive violence, may cause the contents of the vessel to be scattered about.
Strong sulphuric acid chars most organic substances. From substances such as wood, sugar, paper, starch, it withdraws the elements of water, liberating carbon. Since it acts in the same way upon human flesh, it is clear that the concentrated acid must be handled with very great care, for it causes most painful burns. For this reason, vitriol throwing has always been regarded as a most serious and dastardly offence. A simple first-aid remedy for burns produced by sulphuric acid is the liberal application of an emulsion of linseed oil and lime water. The lime, being an alkali, neutralizes the acid, and the oil excludes air from the wound.
The readiness with which sulphuric acid combines with water is often made use of both in the laboratory and in industrial Chemistry for the purpose of drying gases. One illustration of this use has already been given in describing the contact process. Another instance which may be fairly familiar occurs in the case of liquefying air, where the gas must be thoroughly dried before being passed into the refrigerating apparatus, otherwise this would soon become blocked with ice.