t method of making soda from common salt was discovered by
Le Blanc at the end of the last century. It was a rich boon for
France, and became of the highest importance during the wars of
Napoleon. In a very short time it was manufactured to an
extraordinary extent, especially at the seat of the soap
manufactories. Marseilles possessed for a time a monopoly of soda
and soap. The policy of Napoleon deprived that city of the
advantages derived from this great source of commerce, and thus
excited the hostility of the population to his dynasty, which became
favourable to the restoration of the Bourbons. A curious result of
an improvement in a chemical manufacture! It was not long, however,
in reaching England.

In order to prepare the soda of commerce (which is the carbonate)
from common salt, it is first converted into Glauber's salt
(sulphate of soda). For this purpose 80 pounds weight of
concentrated sulphuric acid (oil of vitriol) are required to 100
pounds of common salt. The duty upon salt checked, for a short time,
the full advantage of this discovery; but when the Government
repealed the duty, and its price was reduced to its minimum, the
cost of soda depended upon that of sulphuric acid.

The demand for sulphuric acid now increased to an immense extent;
and, to supply it, capital was embarked abundantly, as it afforded
an excellent remuneration. The origin and formation of sulphuric
acid was studied most carefully; and from year to year, better,
simpler, and cheaper methods of making it were discovered. With
every improvement in the mode of manufacture, its price fell; and
its sale increased in an equal ratio.

Sulphuric acid is now manufactured in leaden chambers, of such
magnitude that they would contain the whole of an ordinary-sized
house. As regards the process and the apparatus, this manufacture
has reached its acme--scarcely is either susceptible of improvement.
The leaden plates of which the chambers are constructed, requiring
to be joined together with lead (since tin or solder would be acted
on by the acid), this process was, until lately, as expensive as the
plates themselves; but now, by means of the oxy-hydrogen blowpipe,
the plates are cemented together at their edges by mere fusion,
without the intervention of any kind of solder.

And then, as to the process: according to theory, 100 pounds weight
of sulphur ought to produce 306 pounds of sulphuric acid; in
practice 300 pounds are actually obtai