A website entitled "Biographies of Famous Chemists".

A website entitled "History of Chemistry".

Website: "History of Science: Museums, memorials, historical places and exhibits".

Website: "Selected Classic Papers from the History of Chemistry.

Alchemy was an odd mixture of the practical and the mystical. Alchemists explained the change in appearance of chemical substances, such as the properties of alcohol and distillation of wine, by philosophical, religious, and astrological speculations. Widespread by the late Medieval period, alchemy was criticized by university scholars and the church.
Alchemy website.

Aristotle's view of physics and cosmology remained unified despite new philosophical and mathematical criticisms, and questions raised by new experimental evidence. These alternative explanations challenged the orthodox purpose of 15th century science: the illumination of Christian truths.

A physician, Georg Bauer (Agricola) , compiled information from earlier writings, the knowledge of metals craftsmen, and his own observations on minerals into De re metallica . Because of its matter-of-fact style, beautiful illustrations, and completeness, his book set the standards for metallurgical and mining practices for the next century.

Philippus Paracelsus attempted to create a new alchemical basis for medical theory and practice. He believed that illness was the result of an imbalance of three chemical "principles"---related to mercury, salt and sulfur---in the body, and that every disease had a specific chemical cure.

Conrad Gessner was a forerunner of modern naturalists. Gessner's many beautifully illustrated encyclopedias show a delight in understanding real and imaginary plants and animals (such as dragons).

In light of the new experimental approach, a critical re-examination of alchemy took place by Johannes Baptista van Helmont and others. Interest focused on how to distinguish between different substances. Van Helmont devised the first experimental distinction between air and the gases produced by combustion.

Experiments with a new mercury barometer led to demonstrations of the mechanical weight of air and the existence of a vacuum. Robert Boyle's experiments with the new vacuum pump of Otto von Guericke showed that air was an elastic fluid whose pressure varied inversely with its volume.

Robert Boyle embraced the popular aim of science---to reveal experimentally the properties of matter, and to explain those qualities in mechanical terms. His experiments led him to attack traditional notions of elementary chemical substances. A true element, he proposed, cannot be reduced further.

Based on Johann Becher's system of chemical elements, which included the new hypothetical substance "phlogiston," George Stahl devised an elaborate comprehensive chemical theory. Despite some troublesome evidence, the phlogiston theory was able to account for many well-known and newly discovered chemical reactions, and it dominated chemistry for over a century.

Numerous chemists in the 18th century sought to explain chemical reactions by "affinity." For example, some chemists measured the degree to which different acids and bases could neutralize each other and form salts, and then arranged the acids and bases according to their relative affinity for each other.

The first steam engines were built by English inventors having no scientific training. Practical experience with heat the the properties of steam enabled James Watt to devise an economical two-chamber condensing steam engine that set the standard for future industrial and mining steam engines.

It had been commonly believed that the different properties of gases were due to impurities in elementary air. Experiments by Joseph Black , Henry Cavendish , Joseph Priestley , and Karl Scheele demonstrated that different gases with distinct chemical compositions exist, and that air is not an elementary substance after all.

Robert Boyle and Isaac Newton explained the relationship between air pressure and volume as gas atoms behaving like tiny, stationary springs with repulsive forces. Daniel Bernoulli proposed the first dynamic view of gas pressure as gas particles in random motion. The Boyle-Newton static theory prevailed until the mid-19th century.

The industrial revolution greatly increased the demand for chemicals. In France the traditional source of sodium sulfate (seaweed) became too expensive for the soap, glass, and gunpowder industries. Nicholas Leblanc devised an inexpensive, large-scale process for sodium sulfate production, but due to technical and financial problems, his plant only operated for a few years.

Joseph Black's pioneering experiments on heat transfer between chambers containing substances at different temperatures established the modern distinction between temperature and heat, and the notions of specific and latent heats. Black believed his findings supported the popular theory that heat was a weightless, self-repulsive fluid substance: caloric.

Based largely on Priestley's experiments with gases and metals. Antoine Lavoisier carried out careful quantitative investigations. They led him to propose that combustion was the result of the combination of a substance with one of the components of air (later called oxygen ), rather than the release of "phlogiston."

Antoine Lavoisier showed that all his findings on combustion and respiration, acids and metal oxides, and the composition of water and air could be explained in terms of oxygen rather than "phlogiston." The slow and reluctant acceptance of this new oxygen theory marked a revolutionary turning point in chemistry.

Luigi Galvani discovered that a frog's leg twitched when its exposed nerve was touched with two dissimilar metals. This observation led Alessandro Volta to construct the first continuous source of electricity from two different metals immersed in an acid---the battery.

On the basis of painstaking observation and calculation René Haüy formulated the first laws of crystal structure. He classified minerals by their characteristic arrangements, rather than their chemical properties. His work laid the foundation of modern crystallography.

Benjamin Thompson (Count Rumford ) raised doubts in the prevailing theory of heat by showing that unlimited heat could be produced by friction. He had no alternative explanation, however, and failed to alter acceptance of the caloric substance theory.

Antoine Lavoisier's Traité Élémentaire de Chemie clearly presented a systematic reform of chemistry like Newton's Principia had done for physics. Written in a new system of chemical terms, Lavoisier's work reviewed his experiments and oxygen theory. He also presented a new table of elements which closely resembles today's periodic table.

Joseph Proust found experimental evidence that the ratios of different constituents of chemical compounds are fixed. This idea was challenged by Claude Berthollet , who thought that the composition of compounds could vary. Their eight-year dispute was settled in Proust's favor with the acceptance of John Dalton's atomic theory.

The idea that matter is ultimately composed of tiny indivisible particles is ancient, but the first successful quantitative application of this idea to chemistry was not made until the 1800s. Then John Dalton proposed that atoms of different chemical elements differed in size, and he estimated their atomic weights.

Based on careful, quantitative measurements of the volumes of gases in chemical reactions, Joseph Gay-Lussac proposed that all gases combine in simple, fixed proportions by volume. This idea implied that equal volumes of different gases should have the same number of atoms (a predecessor to Avogadro's Hypothesis (see below)), but contrary evidence existed.

The invention of batteries opened up new fields in chemistry. Humphry Davy used large batteries to decompose water and minerals into chemical elements (for example, sodium, potassium, and calcium). Jöns Berzelius formulated a chemical affinity theory based on the notion of polarized atoms, which provided explanations of the composition and decomposition of chemicals.

A website entitled "Elemental and Molecular Heritage: An Internet-based Display"

Fossil studies led Georges Cuvier and Jean Baptiste de Lamarck to the same conclusion: simple organic forms were in the oldest rocks and complex forms were in the recent layers. They disagreed strongly on how to interpret this observation. Cuvier believed that catastrophes happened. Lamarck believed in a gradual transformation of life.

Amadeo Avogadro unified Dalton's atomic theory of chemical elements based on their weight with Gay-Lussac's law of combining volumes by proposing that the particles of gaseous elements were not single atoms, but molecules containing several atoms. Despite his sound reasoning, Avogadro's hypothesis was rejected and ignored by chemists for 40 years.

Widespread doubt in Avogadro's hypothesis led to considerable disagreement about how atoms combine to form compounds, and to questions over the correct chemical formulas for elements and compounds. Some preferred direct "equivalent weights," while William Prout believed that atomic weights were simply exact multiples of hydrogen's atomic weight.

Contrary to the prevailing notion that different chemicals have different crystals, Eilhardt Mitscherlich discovered "isomorphism": substances with equal numbers of atoms, bound in the same way, have the same crystal form. Therefore, any particular crystal form depends solely on the number and arrangement of its atoms, not on its chemical nature.

Complex organic compounds obtained from plants and animals were believed to be products of "vital forces." When Friedrich Wöhler made urea from an inorganic compound (ammonium cyanate), doubts were raised about vitalism. This discovery stimulated others to explore possible connections between organic and inorganic chemistry.

The concept of a "radical" --- a group of atoms that behaves chemically as a unit--- gained widespread attention following the discovery of the "benzoyl" radical. Jean Dumas and August Laurent then added the notion of "substitution": the exchange of an atom of one element for an atom of another left the radical basically unchanged.

Justus von Liebig introduced his students to new methods of organic analysis for chemically determining various processes of animal and plant life. His laboratory was equipped to research the basic molecules of life----carbohydrates, fats, and proteins.

Charles Goodyear discovered (after many unsuccessful attempts) how to keep natural rubber from becoming brittle or sticky with changes in temperature by treating it with sulfur in a heating process called vulcanization . His efforts impoverished his family (he even sold his children's books), and sent him to debtor's prison.

Michael Faraday's greatest contributions to chemistry were his discoveries in electrochemistry. He found that the mass of an element released from its compound is directly proportional to the amount of electrical current passing through a solution, and the substance's chemical equivalent weight.

Nitrous oxide and ether were the first anesthetics used by American dentists and doctors. Ether was ridiculed, but its use quickly spread to England. The control of pain led to a revolution in surgery, because shock to the patient was reduced, and the amount of time that doctors could operate was greatly extended.

Christian Schönbein discovered that nitrocellulose (guncotton) treated with ether and alcohol produced a hard but flexible transparent film. This plastic found immediate use in photography. By improving on its formulation with heat molding, John Hyatt was able to produce the first commercially successful bulk form of "celluloid."

Joseph Le Bel and Jacobus van't Hoff showed that optical isomerism (compounds with identical composition but with different optical properties) was due to asymmetric molecular structures that were mirror images of each other (somewhat like the left and right hand). These studies opened up a new field of chemical analysis of the three-dimensional spatial arrangement of molecules--- stereochemistry .

Louis Pasteur's studies of wine gave him the idea that fermentation was the result of living organisms. The prevailing notion of fermentation had a purely chemical basis. Using flasks of broth, Pasteur demonstrated that organisms had to be introduced for decay to occur, and that they were not generated spontaneously.

Despite evidence, many people still remained unconvinced that the chemical principles which governed both inorganic and organic matter were the same. Marcellin Berthelot's methods and principles of organic synthesis finally convinced most chemists that "vital forces" supposedly controlling organic matter did not exist.

Edward Frankland's experiments with reactions between metals and organic compounds (forming an "organometallic compound") led to the valence concept: an atom of one element could only compound with a definite number of atoms of another element.

While investigating a coal tar derivative (aniline), William Perkin accidentally discovered purple crystals capable of dying silk. After this synthetic dye ("Mauve")became fashionable in Paris and a favorite of Queen Victoria, many other dyes were discovered and marketed. The chemical dye industry grew into a major center of chemical research.

A website entitled "Elemental and Molculear Heritage: An Internet-based Display" which includes a picture of a display with "Perkin's Mauveine".

A website entitled "Materials and Technology" which includes dyes.

The chaos of chemical formulas (there were 15 different ones for acetic acid!) demanded clarification of the concepts of atom and molecule. At the first International Congress of Chemistry at Karlsruhe, Germany, Stanislao Cannizzaro demonstrated how Avogadro's hypothesis could resolve all these questions. A consistent system of atomic weights finally was established.

Website: "Selected Classic Papers from the History of Chemistry (includes papers about Cannizzaro and the Karlsruhe Conference).

Mass action is the effect of the mass of the reacting chemicals on the time it takes for the reaction to reach equilibrium . Norwegians Cato Guldberg and Peter Waage suggested the concept long before it was demonstrated. They formulated a mathematical expression (similar to the equilibrium constant expression) for the effects produced by the mass on the equilibrium of a reaction.

Contributions of Friedrich Kekulé and others helped to establish organic chemistry---the chemistry of carbon atoms---as a scientific study apart from inorganic and physical chemistry. In an unusual flash of insight, Kekulé realized that the carbon atoms in the organic compound benzene (C ₆ H ₆ ) were arranged in a ring (or hexagon), with alternating single and double bonds.

Dmitri Mendeleev and Julius Meyer proposed the first plausible periodic tables: elements arranged according to similar repeating physical and chemical properties, usually in order of increasing atomic weight. They did not attract attention until an element was discovered whose properties were "predicted" by a blank space in Mendeleev's table.

A website entitled "WebElements Periodic Table"

A website which is entitled "WebElements".

A new science of thermodynamics gave chemists an ability to explain for the first time why many reactions took place. For example, Josiah Gibbs' "phase rule" was a simple mathematical equation of the conditions necessary for various substances in different phases to be in equilibrium.

Emil Fischer discovered a reagent that enabled him to separate and synthesize simple sugars (glucose and fructose) from simpler chemicals. Based on this work and the rules of stereochemistry, he was able to account for their various asymmetrical structures. His work became the basis of carbohydrate chemistry.

The pressure and electrical conductivity of molecules in solutions were explained by two different approaches. Jacobus van't Hoff showed how osmotic pressure was proportional to temperature, just like in gases. Electrical conductivity of dilute solutions was due to the breaking up of salts into polarized ions (positively or negatively charged), said Svante Arrhenius .

Alfred Werner thought tht large molecules of inorganic compounds are made up of a central metal atom (or ion) surrounded by groups of atoms (or ions) in simple geometric patterns. This idea was not well received in Werner's lifetime, because important physical evidence to support his model was missing at the time.

William Ramsay found a way to isolate an unknown part of air and named it argon, from the Greek word meaning "lazy one," because this element did not react chemically with other elements. Three other "noble" (unreactive) gases (neon, krypton and xenon) in air were identified by Ramsay.

Antoine Becquerel found that uranium salts gave off radiation (a uranium ore spoiled a photographic plate). Soon two other "radioactive" elements were found by Pierre and Marie Curie . These discoveries led to the recognition that radioactivity involved the atomic transmutation of one element into another---a successive decay---until a stable element remained.

Despite many studies of chemical and physical properties of proteins in the late 19th century, the details of protein structure remained a mystery. Emil Fischer was the first to break proteins down into their individual amino acids and then recombine those amino acids into protein-like molecules. His quantitative methods set the standard for future organic and protein chemistry.

Professor Frederick S. Kipping (University of Nottingham) does pioneering research on silicone polymers. His work forms the basis for worldwide development of the synthetic rubber and silicone-based lubricant industries.

Around 1895, a group of well-known scientists (called the "energeticists") challenged the idea that matter was made of up atoms. Jean Perrin's experiments with Brownian motion (which used some of Einstein's ideas) provided convincing evidence that atoms did in fact exist.

Mikhail Tswett developed a process called chromatography. In it, components of mixtures can be separated, creating colored bands in the absorptive medium. Later, modifications of chromatography were used to isolate and identify the amino acids of complex protein molecules as well as many other types of compounds.

An online book on chromatography.

The combination of nitrogen and hydrogen gases in the presence of a catalyst and high pressure and temperature produces ammonia . The optimization of this synthesis was the achievement by Fritz Haber that started the synthetic chemical fertilizer industry which made possible worldwide increases in agricultural production.

Frederick Soddy suggested that atoms of the same element with the same chemical properties could differ in weight. These elements were later termed "isotopes." They were verified by Joseph John Thomson with a spectrograph that separated elements by their masses using electric and magnetic fields.

The chemical structures of bile acids and steroids were uncertain and unrelated until Heinrich Wieland and Adolf Windaus synthesized these compounds from the same "parent" acid. This work greatly advanced the understanding of the role played by these compounds in healthy and diseased organisms.

Hermann Staudinger's clever theoretical and experimental studies showed how polymers--gigantic molecules made of long chains of tens of thousands of atoms---could be created. Further research and manufacturing efforts led to the development of new synthetic plastics, such as polystyrene, polypropylene, and polyethylene.

A website entitled "Development of the Detergent Industry"

Linus Pauling and Alfred Mirsky proposed that the amino acid chains in proteins were not simply long straight strings of molecules but were folded around in the shape of a spring, an "alpha helix." This model not only agreed well with the available chemical data on proteins, but also provided a powerful new method for determining the three-dimensional structure of proteins.

A website entitled "Common Molecules Collection" which has thumbnail images of molecules.

Fifteen years after the discovery of artificial nuclear disintegrations, Irène Joliot-Curie and Frédéric Joliot-Curie created a new radioactive element that emitted positrons (or positively charged beta particles). Their discovery inspired new experiments that led five years later to the discovery of nuclear fission.

Energy for cell processes is stored in high energy phosphate bonds. Hans Krebs identified the cycle of enzyme-catalyzed reactions necessary for the generation of those high-energy phosphate bonds.

Aleksandr Oparin suggested that if the essential organic materials (carbon, hydrogen, nitrogen and oxygen) were available in the Earth's primeval environment, then the first life forms could have arisen spontaneously. Stanley Miller recreated such an environment in his laboratory, and using electrical discharges to similate lightning, produced life's basic amino acids.

Otto Hahn's radiochemical experiments and Lise Meitner's explanations led to the unexpected realization that certain atoms could be split into two nearly equal massive elements. Scientists immediately realized that the chain reactions of such nuclear fission would release enormous energy---making possible a potentially devastating bomb.

Experimental efforts are presently lagging behind the theoretical work of Ilya Prigogine . He started a new school of thought about nonequilibrium chemical thermodynamics that explains how "orderly" processes such as prebiological evolution can take place naturally under the Second Law of Thermodynamics. His work has influenced scientists in many fields.

All living things contain a small amount of radioactive carbon (carbon-14), which remains constant until they die. Willard Libby devised "carbon dating" ---a way to tell the age of remains up to 50,000 years old by knowing the rate of decay and measuring the amount of radioactive carbon left.

Helium, neon, argon, krypton, xenon and radon gases were thought to have the remarkable property of not bonding with other elements. Hence, they were called inert or "noble" gases. When Neil Bartlett discovered the first inert gas compound (xenon hexafluoroplatinate), theoretical questions immediately arose about how these gases could form chemically bound compounds.

Environmental Protection Agency established; "Earth Day" demonstrations reflect popular support for improved monitoring and protection of the environment.

The Environmental Protection Agency website.

A website entitled "Environmental Molecules".