SULPHURIC ACID. OIL OF VITRIOL. or when hydrated, HO, This important article of manufacture, of which nearly a hundred thousand tons are made annually in Great Britain, is in general pro duced by burning together in a furnace a mixture of sulphur and nitre, the proportions varying from the one-eighth to the one-twentieth part of nitre.
The fumes are collected in immense leaden chambers, the bottoms of which are covered with water, which absorbs the vapour and becomes impregnated with sulphuric acid. When the water has acquired the S. G. of about P25, it is drawn off and evaporated by boiling in shallow leaden vessels till it acquires the S. G. of 1. 7, when it would begin to act upon the lead. The evaporation is then completed in platinum vessels till the acid reaches the S. G. P845. The manufacture is then finished and the concentrated acid is trans ferred to carboys, (large glass bottles covered with wickerwork,) which contain 100 lbs.
Sulphuric acid of the S. G. P845 contains anhydrous sulphuric acid plus one atom of water. It is a limpid, inodorous, colourless,
and very heavy liquid of an oily consistence. It boils at a heat of 620°, and distils over without decomposition. No fumes arise from it. A piece of polished zinc suspended above it in a closed bottle remains untarnished for many months. It has a strong affinity for water, and if 4 parts of it are added to one of water at the freezing point, the temperature of the mixture speedily rises to 212°.
Commercial oil of vitriol is tolerably pure. The principal impurity is sulphate of lead, which is detected by its producing a white turbidity when the acid is diluted with distilled water.
Nordhausen oil of vitriol is a dark coloured fuming sulphuric acid, composed of a mixture of anhydrous and hydrated sulphuric acid. It is manufactured in Germany.
Anhydrous sulphuric acid is a tenacious crystalline mass, which in the absence of all moisture has no acid properties. When water is added to it, combination takes place, with heat, light and ex plosion.