88 POISONS : THEIR EFFECTS AND DETECTION. [§§ 58-60. 
ordinary atmosphere, increase to nearly 4 in twenty-four hours ; in 
common with all acids, it reddens litmus, yellows cochineal, and changes 
all vegetable colours. There is another form of sulphuric acid, ex¬ 
tensively used in the arts, known under the name of “ Nordhausen 
sulphuric acid,” “ fuming acid,” formula H 2 S 2 0 4 . This acid is produced 
by the distillation of dry ferrous sulphate, at a nearly white heat— 
either in earthenware or in green glass retorts ; the distillate is received 
in sulphuric acid. As thus manufactured, it is a dark fuming liquid, 
of T9 specific gravity, and boiling at 53°. When artificially cooled 
down to 0°, the acid gradually deposits crystals, which consist of a 
definite compound of 2 atoms of anhydrous sulphuric acid and 1 atom 
of water. There is some doubt as to the molecular composition of 
Nordhausen acid ; it is usually considered as hydric sulphate saturated 
with sulphur dioxide. This acid is manufactured chiefly in Bohemia, 
and is used, on a large scale, as a solvent for alizarine. 
§ 58. Sulphur Trioxide, or Sulphuric Anhydride (S0 3 ), itself may 
be met with in scientific laboratories, but is not in commerce. Sulphur 
trioxide forms thin needle-shaped crystals, arranged in feathery groups. 
Seen in mass, it is white, and has something the appearance of asbestos. 
It fuses to a liquid at about 18°, boils at 35°, but, after this operation 
has been performed, the substance assumes an allotropic condition, and 
then remains solid up to 100° ; above 100° it melts, volatilises, and 
returns to its normal condition. Sulphuric anhydride hisses when it 
is thrown into water, chemical combination taking place and sulphuric 
acid being formed. Sulphur trioxide is excessively corrosive and 
poisonous. 
§ 59. Sulphuric acid, in the free state, may not infrequently be found 
in nature. The senior author has had under examination an effluent 
water from a Devonshire mine, which contained more than one grain 
of free sulphuric acid per gallon, and was accused, with justice, of 
destroying the fish in a river. It also exists in large quantities in 
volcanic springs. In a torrent flowing from the volcano of Parce, in 
the* Andes, Boussingault calculated that 15,000 tons of sulphuric acid 
and 11,000 tons of hydrochloric acid were yearly carried down. In the 
animal and vegetable kingdoms, sulphuric acid exists, as a rule, in 
combination with bases, but there is an exception in the saliva of the 
Dolium galea , a Sicilian mollusc. 
§ 60. Statistics. —When something like 900,000 tons of sulphuric 
acid are produced annually in England alone, and when it is considered 
that sulphuric acid is used in the manufacture of most other acids, in 
the alkali trade, in the manufacture of indigo, in the soap trade, in the 
manufacture of artificial manure, and in a number of technical processes, 
there is no cause for surprise that it should be the annual cause of 
many deaths. 
