The water at the bottom of the cham ber thus becomes loaded with sulphuric acid ; when a certain degree of strength has been reached, it is drawn off and con centrated by evaporation, first in leaden pans, and afterwards in stills of platinum, until it attains a density (when cold) of 1:84, or thereabouts ; it is then transferred to carboys, or large glass bottles fitted in baskets, for sale. An inferior kind of acid is now made by burning iron pyrites, or poor copper ore, as a substitute for Si cilian sulphur ; this is chiefly used by the makers for their own consumption ; it very frequently contains arsenic.
Sulphuric acid is a limpid colorless fluid, of a spec. gray. of 1:8. It boils at 620° ; it freezes at 15°. But the temper ature at which the diluted acid congeals is singularly modified by the quantity of water which it contains. When of the spec. gray. of 118 (which may be regard ed as a compound of 1 atom of dry acid and 2 of water), it freezes at 40°, and re mains solid for a long time at several de grees above that point : if the density be either diminished or increased, a greater cold is required to congeal it.
It is acrid and caustic, and intensely acid in all its characters, even when largely diluted. Its attractions for bases is such that it separates or expels all other acids more or less perfectly from their combinations. Its affinity for water is such that it rapidly absorbs it from the atmosphere, and when mixed with water much heat is evolved ; thus by suddenly mixing 4 of the acid and 1 of water at 60', the temperature rises to 300°. Its attraction for water also causes the sudden liquefaction of snow ; and if mix ed with it in due proportion, an intense cold is the consequence. It acts ener getically upon animal and vegetable sub stances, generally charring them, and often, as in the case of sugar, with singu lar rapidity.
The acid, as it usually occurs in com merce, under the name of concentrated sulphuric acid, is a compound of 1 atom of anhydrous acid and 1 of water. The anhydrous sulphuric acid is constituted of 16 sulphur (1 atom), and 24 oxygen (3 atoms); its equivalent, therefore, is 16-1-24=40: this is the composition of the acid as it exists in the anhydrous sul phates. The strongest liquid acid con sists of 40 of the dry or anhydrous acid (1 atom), and 9 water (1 atom), and is therefore represented by the equivalent 40+9=49.
Sulphurous acid.—A compound of 1 equivalent of sulphur and 2 equivalents of oxygen : It is a gas which is poison ous, producink .,uffocation. It may be made by burning sulphur in a chamber with air when the acid vapors rise. It is also Made by boiling sulphuric acid with charcoal or carbonaceous matter, when the sulphuric loses its oxygen and is con verted into sulphurous acid.
It is found to escape in torrents from the mouths of volcanoes ; and it is gener ally believed that its caused the death of Pliny the elder, A.D. 99. It is found that this acid is the only mate rial with which woollens and silks can be bleached, and its application to this pur pose is very simple and extensive. Sul phurous acid is soluble in water, but this solution had no application until of late years. It is now used for destroying co lors. There is a substance imported in to England from the Cape of Good Hope, called jute, which had hitherto been con sidered of no use, from the supposed im possibility of bleaching its fibre ; but this has lately been effected, and a white and silky appearance imparted to it. Sul phurous acid is the only thing by which this bleaching can be effected ; for if placed in an alkaline liquor, jute is re duced into a soft pulpy state.