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provide sodium carbonate for England, thus driving up
its cost.
Sensing the urgency for a better source of alkali
for France, the French Academy of Sciences, in 1783,
offered a prize to the person who could develop the most
efficient and economic method of producing soda ash
from common salt (sodium chloride), which was read-
ily available. Nicolas Leblanc (1742-1806), encour-
aged by the competition, began experimenting in 1784
to find a new process. In 1789, he devised a two-step
set of reactions to produce soda ash. In the first step,
he dissolved common salt into a sulfuric acid solution
at high temperature (800 C-900 C) in an iron pan to
produce dissolved sodium sulfate ( Glauber's salt ) and
hydrochloric acid gas by
practice, the reaction was incomplete and produced
gas-phase sulfuric acid and soot as well. The sodium
carbonate residue was separated from calcium sul-
fide by adding water, which preferentially dissolved
the sodium carbonate. The resulting solution was then
dried, producing sodium carbonate crystals. Finally,
sodium carbonate was combined with animal fat to pro-
duce soap.
A necessary ingredient for the production of sodium
carbonate was aqueous sulfuric acid (Reaction 10.1).
One source of sulfur was combustion of elemental sul-
fur (S) powder with saltpeter [KNO 3 (s)], and then dis-
solving the resulting H 2 SO 4 (g) in water, as was done by
Libavius in 1585. This process was inefficient, releas-
ing volumes of gas-phase sulfuric acid and nitric oxide
[NO(g)] (which converts to nitrogen dioxide and then
to nitric acid in air). Another source was the burning
of iron pyrites [FeS 2 (s)] and arsenopyrites [FeAsS 2 (s)].
Burning of the latter resulted in the release of arsenic
vapor, which was emitted to the air along with the other
pollutants.
In sum, although the production of sodium carbonate
from common salt and sulfuric acid allowed the alkali
industry to become self-sufficient and escape reliance
on the import of natural sodium carbonate, it resulted
in the release of HCl(g), H 2 SO 4 (g), HNO 3 (g), and soot,
causing widespread acid deposition and air pollution in
France and the UK (Figure 10.1a). The Leblanc pro-
cess also produced large amounts of impure solid alkali
waste containing calcium sulfide. The waste was piled
near each factory and commonly referred to as galligu ,
a name ascribed specifically to waste from the Leblanc
process. When rainwater fell on the waste, some of the
High
temperatu re
2NaCl(s)
Sodium
chloride
+
H 2 SO 4 (a q)
Sulfuric
acid
Na 2 SO 4 (a q)
Sodium
sulfate
+
2HCl(g)
Hydrochloric
acid
(10.1)
In the second step, he heated sodium sulfate together
with charcoal and chalk in a kiln to form sodium car-
bonate by
High
temperatu re
Na 2 SO 4 (aq)
Sodium
sulfate
+
2C
Carbon
from
charcoal
+
CaCO 3 (s)
Calcum
carbonate
from chalk
Na 2 CO 3 (aq)
Sodium
carbonate
+
CaS(s)
+
2CO 2 (g)
Carbon
dioxide
(10.2)
Calcium
sulfide
By-products of the second reaction, when complete,
included calcium sulfide [CaS(s)], an odorous, yellow-
to-light
gray
powder,
and
carbon
dioxide
gas.
In
(a)
(b)
Figure 10.1. (a) Alkali factory emissions in the industrial town of Widnes, Cheshire County, England, in the
early 1800s. Courtesy Halton Borough Council, UK; www.ceb.cam.ac.uk/exemplarch2002/mcp21/leblanc.jpg.
(b) Piles of waste galligu from an alkali factory. Courtesy Halton Borough Council, UK; www2.halton.gov.uk/
images/main/conlanddittonalps.
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