Modern Engineering Thermodynamics

592 CHAPTER 15: Chemical Thermodynamics
IS IT CHEMISTRY OR ALCHEMY?
A practical chemical technology can be traced to prehistoric times. Primitive metallurgy, medicine, and food preparation are
typical examples. They were purely empirical “recipe” driven processes with no form of chemical theory to explain their
results. Before the sixth century BC, it was generally believed that all things were composed of a single primitive element.
The Greek philosophers Heraclitus (540–480 BC) and Empedocles (490–430 BC) began a new era when they proposed that,
instead of a single element, all matter was made up of four elements—air, earth, fire, and water—and that the continual
mixing of these elements formed all the objects of the real world.
The Greek philosopher Pythagoras (580–500 BC) is generally credited with recognizing the functional significance of numbers
in quantifying the processes of the real world. Pythagoras established an academy of learning in Crotona, Italy, in
about 532 BC. The academy prospered long after his death until its destruction in about 390 BC. It is believed that his disciples
(known as Pythagoreans) working at the academy during this time developed many of the mathematical discoveries
now attributed to him (e.g., the Pythagorean theorem for right triangles).
Empedocles adopted Pythagoras’ numerology technique in an attempt to quantify the chemistry of his four elements. For
example, according to Empedocles, animal bone consisted of two parts water, two parts earth, and four parts fire. Because
he believed that all of his four elements were most thoroughly mixed in blood, he concluded that people think mainly
with their blood.
From about the second century AD until nearly the 19th century, the world embraced what is considered today to be a
scientific and chemical curiosity, alchemy. Alchemy was a combination of the occult, astrology, and primitive chemistry.
Even its name, derived from Arabic and introduced in the 12th century, is obscure because the root chem seems to have no
relevant etymological meaning.
The basic function of alchemy was transmutation, which was concerned with transmuting age to youth, sickness to health,
death to immortality. More notorious was its preoccupation with the physical transmutation of base metals into gold (i.e.,
transmuting poverty to wealth). Its central elements were mercury (quicksilver, the liquid metal), sulfur (the stone that
burns), and ammonium chloride (sal ammoniac, a source of hydrochloric acid). Successful alchemists tended to be charlatans
whose work was shrouded in mystery. From the Medieval period forward, the central focus of alchemy was the making
of gold (religion had successfully taken over the immortality issue), and many prominent scientists, including Isaac Newton
(1643–1726), experimented with it seriously. (Newton is thought to have contracted mercury poisoning in about 1690 as a
result of his alchemy experiments.) The false science of alchemy, which appealed primarily to the human weakness of
greed, went without serious intellectual challenge for nearly 2000 years.
In the 17th century, Johann Jochim Becher (1635–1682), an established alchemist at one time engaged in attempting to
transmute Danube River sand into gold, proposed that all substances were made up of the classical alchemical elements of
mercury, sulfur, and corrosive salts, plus a new fourth weightless element that was produced by combustion. In 1697, the
German physician Georg Ernst Stahl (1660–1734) named this supposed fourth element phlogiston and used it to develop a
coherent theory of combustion, respiration, and corrosion. His phlogiston theory quickly won universal scientific approval
and was the only scientifically accepted theory of matter for nearly 100 years afterward.
In 1774, the English clergyman and scientist Joseph Priestley (1733–1804) described some of his experimental results in
removing phlogiston from air (the “dephlogistication” of air) to the French chemist Antione Laurent Lavoisier (1743–
1794), who immediately recognized their importance and subsequently carried out similar experiments himself. Lavoisier
soon realized that the dephlogiston that Priestley thought he had been working with was actually a unique chemical and,
in 1777, he named it oxygen (from the Greek for acid forming). By the early 19th century Lavoisier’s oxidation theory completely
replaced Stahl’s phlogiston theory and the era of modem chemistry had begun. Lavoisier had done for chemistry
what a century earlier Newton had done for mechanics; he put the subject on a firm analytical foundation. The unfortunate
Joseph Priestley was subsequently driven from his home in England because of his public support of the French Revolution,
and he settled in America.
WHO KILLED THE GREAT FRENCH CHEMIST LAVOISIER?
Because Lavoisier maintained a career in the French government as well as science (he was on the original 1790 weights
and measures committee that led to the development of the metric system we now use), he was caught up in the French
Revolution and was accused of political crimes (such as stopping the circulation of air in Paris by a city wall erected at his
suggestion in 1787). He was convicted and guillotined on the same day in 1794.