The history of chemistry represents a time span from ancient history to the present. By 1000 BC, civilizations used technologies that would eventually form the basis of the various branches of chemistry. Examples include the discovery of fire, extracting metals from ores, making pottery and glazes, fermenting beer and wine, extracting chemicals from plants for medicine and perfume, rendering fat into soap, making glass, and making alloys like bronze. The protoscience of chemistry, alchemy, was unsuccessful in explaining the nature of matter and its transformations. However, by performing experiments and recording the results, alchemists set the stage for modern chemistry. The history of chemistry is intertwined with the history of thermodynamics, especially through the work of Willard Gibbs.
Ancient history
Early humans
Fire
Arguably the first chemical reaction used in a controlled manner was fire. However, for millennia fire was seen simply as a mystical force that could transform one substance into another (burning wood, or boiling water) while producing heat and light. Fire affected many aspects of early societies. These ranged from the simplest facets of everyday life, such as cooking and habitat heating and lighting, to more advanced uses, such as making pottery and bricks and melting of metals to make tools. It was fire that led to the discovery of glass and the purification of metals; this was followed by the rise of metallurgy.
Paint
A 100,000-year-old ochre-processing workshop was found at Blombos Cave in South Africa. It indicates that early humans had an elementary knowledge of mineral processing. Paintings drawn by early humans consisting of early humans mixing animal blood with other liquids found on cave walls also indicate a small knowledge of chemistry.
Early metallurgy
The earliest recorded metal employed by humans seems to be gold, which can be found free or "native". Small amounts of natural gold have been found in Spanish caves used during the late Paleolithic period, around 40,000 BC. The earliest gold metallurgy is known from the Varna culture in Bulgaria, dating from c. 4600 BC. Silver, copper, tin and meteoric iron can also be found native, allowing a limited amount of metalworking in ancient cultures. Egyptian weapons made from meteoric iron in about 3000 BC were highly prized as "daggers from Heaven". During the early stages of metallurgy, methods of purification of metals were sought, and gold, known in ancient Egypt as early as 2900 BC, became a precious metal.
Bronze Age
Tin, lead, and copper smelting Certain metals can be recovered from their ores by simply heating the rocks in a fire: notably tin, lead and (at a higher temperature) copper. This process is known as smelting. The first evidence of this extractive metallurgy dates from the 6th and 5th millennia BC, and was found in the archaeological sites of the Vinča culture, Majdanpek, Jarmovac and Pločnik in Serbia. The earliest copper smelting is found at the Belovode site; these examples include a copper axe from 5500 BC. Other signs of early metals are found from the third millennium BC in places like Palmela (Portugal), Los Millares (Spain), and Stonehenge (United Kingdom). However, as often happens in the study of prehistoric times, the ultimate beginnings cannot be clearly defined and new discoveries are ongoing.
Bronze These first metals were single elements, or else combinations as naturally occurred. By combining copper and tin, a superior metal could be made, an alloy called bronze. This was a major technological shift that began the Bronze Age about 3500 BC. The Bronze Age was a period in human cultural development when the most advanced metalworking (at least in systematic and widespread use) included techniques for smelting copper and tin from naturally occurring outcroppings of copper ores, and then smelting those ores to cast bronze. These naturally occurring ores typically included arsenic as a common impurity. Copper/tin ores are rare, as reflected in the absence of tin bronzes in western Asia before 3000 BC. After the Bronze Age, the history of metallurgy was marked by armies seeking better weaponry. States in Eurasia prospered when they made the superior alloys, which, in turn, made better armor and better weapons. The Chinese were credited with the first ever use of Chromium to prevent rusting, until this was disproven in 2019. This technique was thought to have been used, for example, to protect bronze artifacts such as arrowheads and sword blades buried as grave goods in the mausoleum of the First Emperor of Qin. However, a detailed scientific investigation in revealed that the chromium found on these artifacts originated naturally from the lacquer applied to them. Scientists now believe that the excellent preservation of the artifacts was not due to intentional chromium plating, but rather to the burial environment . Prior to this, archaeologists discovered that bronze-tipped crossbow bolts at the tomb of Qin Shi Huang showed no sign of corrosion after more than 2,000 years, which they believed was because they had been coated in chromium. Chromium was not used anywhere else until the experiments of French pharmacist and chemist Louis Nicolas Vauquelin (1763–1829) in the late 1790s. In multiple Warring States period tombs, sharp swords and other weapons were also found to be coated with 10 to 15 micrometers of chromium oxide, which left them in pristine condition to this day. Significant progress in metallurgy and alchemy was also made in ancient India.
Iron Age
Ferrous metallurgy The extraction of iron from its ore into a workable metal is much more difficult than copper or tin. While iron is not better suited for tools than bronze (until steel was discovered), iron ore is much more abundant and common than either copper or tin, and therefore more often available locally, with no need to trade for it. Iron working appears to have been invented by the Hittites in about 1200 BC, beginning the Iron Age. The secret of extracting and working iron was a key factor in the success of the Philistines. Cast iron smithing as well as the innovation of the Blast Furnace and Cupola furnace was invented in ancient China, during the Warring States period when armies sought to develop better weaponry and armor in state-armories. Many other applications, practices, and devices associated with or involved in metallurgy were also established in ancient China, with the innovations of hydraulic-powered trip hammers, and double-acting piston bellows. The Iron Age is named after the advent of iron working (ferrous metallurgy). Historical developments in ferrous metallurgy can be found in a wide variety of past cultures and civilizations. These include the ancient and medieval kingdoms and empires of the Middle East and Near East, ancient Iran, ancient Egypt, ancient Nubia, and Anatolia (Turkey), Ancient Nok, Carthage, the Greeks and Romans of ancient Europe, medieval Europe, ancient and medieval China, ancient and medieval India, ancient and medieval Japan, amongst others.
Classical antiquity and atomism
Philosophical attempts to rationalize why different substances have different properties, such as color, density, smell; exist in different states, such as solid, liquid, or gas; and react in a different manner when exposed to environments, for example temperature changes in fire or water, led ancient philosophers to postulate the first theories on nature and chemistry. The history of such philosophical theories that relate to chemistry can likely be traced back to every single ancient civilization. The common aspect in all these theories was the attempt to identify a small number of primary classical elements that make up all the various substances in nature. Substances like air, water, and soil/earth, energy forms, such as fire and light, and more abstract concepts such as thoughts, aether, and heaven, were common in ancient civilizations even in the absence of any cross-fertilization: for example ancient Greek, Indian, Mayan, and Chinese philosophies all considered air, water, earth and fire as primary elements.
Ancient world Around 420 BC, Empedocles stated that all matter is made up of four elemental substances: earth, fire, air and water. Atomism in multiple different forms appeared in ancient Greece. Greek atomism was made popular by the Greek philosopher Democritus, who declared that matter is composed of indivisible and indestructible particles called "atomos" around 380 BC. Earlier, Leucippus also declared that atoms were the most indivisible part of matter. This coincided with a similar declaration by the Indian philosopher Kanada in his Vaisheshika sutras around the same time period. Aristotle opposed the existence of atoms in 330 BC. A Greek text attributed to Polybus the physician (ca. 380 BC) argued that the human body is composed of four humours instead. Epicurus (fl. 300 BC) postulated a universe of indestructible atoms in which man himself is responsible for achieving a balanced life. With the goal of explaining Epicurean philosophy to a Roman audience, the Roman poet and philosopher Lucretius wrote De rerum natura (On the Nature of Things) in the middle of the first century BC. In the work, Lucretius presents the principles of atomism; the nature of the mind and soul; explanations of sensation and thought; the development of the world and its phenomena; and explains a variety of celestial and terrestrial phenomena. The earliest alchemists in the Western tradition seemed to have come from Greco-Roman Egypt in the first centuries AD. In addition to technical work, many of them invented chemical apparatuses. The bain-marie, or water bath, is named for Mary the Jewess. Her work also gives the first descriptions of the tribikos and kerotakis. Cleopatra the Alchemist described furnaces and has been credited with the invention of the alembic. Later, Zosimos of Panopolis wrote books on alchemy, which he called cheirokmeta, the Greek word for "things made by hand." These works include many references to recipes and procedures, as well as descriptions of instruments. Much of the early development of purification methods were described earlier by Pliny the Elder in his Naturalis Historia. He tried to explain those methods, as well as making acute observations of the state of many minerals.
Medieval alchemy
The elemental system used in medieval alchemy was developed primarily by Jābir ibn Hayyān and was rooted in the classical elements of Greek tradition. His system consisted of the four Aristotelian elements of air, earth, fire, and water in addition to two philosophical elements: sulphur, characterizing the principle of combustibility, "the stone which burns"; and mercury, characterizing the principle of metallic properties. They were seen by early alchemists as idealized expressions of irreducible components of the universe and are of larger consideration within philosophical alchemy. The three metallic principles (sulphur to flammability or combustion, mercury to volatility and stability, and salt to solidity) became the tria prima of the Swiss alchemist Paracelsus. He reasoned that Aristotle's four-element theory appeared in bodies as three principles. Paracelsus saw these principles as fundamental and justified them by recourse to the description of how wood burns in fire. Mercury included the cohesive principle, so that when it left the wood (in smoke) the wood fell apart. Smoke described the volatility (the mercurial principle), the heat-giving flames described flammability (sulphur), and the remnant ash described solidity (salt).
The philosopher's stone
Alchemy is defined by the Hermetic quest for the philosopher's stone, the study of which is steeped in symbolic mysticism, and differs greatly from modern science. Alchemists toiled to make transformations on an esoteric (spiritual) and/or exoteric (practical) level. It was the protoscientific, exoteric aspects of alchemy that contributed heavily to the evolution of chemistry in Greco-Roman Egypt, in the Islamic Golden Age, and then in Europe. Alchemy and chemistry share an interest in the composition and properties of matter, and until the 18th century they were not separate disciplines. The term chymistry has been used to describe the blend of alchemy and chemistry that existed before that time. During the Renaissance, exoteric alchemy remained popular in the form of Paracelsian iatrochemistry, while spiritual alchemy flourished, realigned to its Platonic, Hermetic, and Gnostic roots. Consequently, the symbolic quest for the philosopher's stone was not superseded by scientific advances, and was still the domain of respected scientists and doctors until the early 18th century. Early modern alchemists who are renowned for their scientific contributions include Jan Baptist van Helmont, Robert Boyle, and Isaac Newton.
Alchemy in the Islamic world
In the Islamic World, the Muslims were translating the works of ancient Greek and Hellenistic philosophers into Arabic and were experimenting with scientific ideas. The Arabic works attributed to the 8th-century alchemist Jābir ibn Hayyān introduced a systematic classification of chemical substances, and provided instructions for deriving an inorganic compound (sal ammoniac or ammonium chloride) from organic substances (such as plants, blood, and hair) by chemical means. Some Arabic Jabirian works (e.g., the "Book of Mercy", and the "Book of Seventy") were later translated into Latin under the Latinized name "Geber", and in 13th-century Europe an anonymous writer, usually referred to as pseudo-Geber, started to produce alchemical and metallurgical writings under this name. Influential scholars, such as Abū al-Rayhān al-Bīrūnī and Avicenna disputed the theories of alchemy, particularly the theory of the transmutation of metals. During the period of Islamic Alchemy, works attributed to Geber correctly identified sulfur and mercury as elements.
Problems encountered with alchemy There were several problems with alchemy, as seen from today's standpoint. There was no systematic naming scheme for new compounds, and the language was esoteric and vague to the point that the terminologies meant different things to different people. In fact, according to The Fontana History of Chemistry (Brock, 1992):
The language of alchemy soon developed an arcane and secretive technical vocabulary designed to conceal information from the uninitiated. To a large degree, this language is incomprehensible to us today, though it is apparent that readers of Geoffrey Chaucer's Canon's Yeoman's Tale or audiences of Ben Jonson's The Alchemist were able to construe it sufficiently to laugh at it.
Chaucer's tale exposed the more fraudulent side of alchemy, especially the manufacture of counterfeit gold from cheap substances. Less than a century earlier, Dante Alighieri also demonstrated an awareness of this fraudulence, causing him to consign all alchemists to the Inferno in his writings. Soon afterwards, in 1317, the Avignon Pope John XXII ordered all alchemists to leave France for making counterfeit money. A law was passed in England in 1403 which made the "multiplication of metals" punishable by death. Despite these and other apparently extreme measures, alchemy did not die. Royalty and privileged classes still sought to discover the philosopher's stone and the elixir of life for themselves. There was also no agreed-upon scientific method for making experiments reproducible. Indeed, many alchemists included in their methods irrelevant information such as the timing of the tides or the phases of the moon. The esoteric nature and codified vocabulary of alchemy appeared to be more useful in concealing the fact that they could not be sure of very much at all. As early as the 14th century, cracks seemed to grow in the facade of alchemy; and people became sceptical. Clearly, there needed to be a scientific method in which experiments could be repeated by other people, and results needed to be reported in a clear language that laid out both what was known and what was unknown.
17th and 18th centuries: Early chemistry
Practical attempts to improve the refining of ores and their extraction to smelt metals was an important source of information for early chemists in the 16th century, among them Georg Agricola (1494–1555), who published his great work De re metallica in 1556. His work describes the highly developed and complex processes of mining metal ores, metal extraction and metallurgy of the time. His approach removed the mysticism associated with the subject, creating the practical base upon which others could build. The work describes the many kinds of furnace used to smelt ore, and stimulated interest in minerals and their composition. It is no coincidence that he gives numerous references to the earlier author, Pliny the Elder and his Naturalis Historia. Agricola has been described as the "father of metallurgy" and the founder of geology as a scientific discipline. In 1605, Sir Francis Bacon published The Proficience and Advancement of Learning, which contains a description of what would later be known as the scientific method. In 1605, Michal Sedziwój publishes the alchemical treatise A New Light of Alchemy which proposed the existence of the "food of life" within air, much later recognized as oxygen. In 1615 Jean Beguin published the Tyrocinium Chymicum, an early chemistry textbook, and in it draws the first-ever chemical equation. In 1637 René Descartes publishes Discours de la méthode, which contains an outline of the scientific method. The Dutch chemist Jan Baptist van Helmont's work Ortus medicinae was published posthumously in 1648; the book is cited by some as a major transitional work between alchemy and chemistry, and as an important influence on Robert Boyle. The book contains the results of numerous experiments and establishes an early version of the law of conservation of mass. Working during the time just after Paracelsus and iatrochemistry, Jan Baptist van Helmont suggested that there are insubstantial substances other than air and coined a name for them – "gas", from the Greek word chaos. In addition to introducing the word "gas" into the vocabulary of scientists, van Helmont conducted several experiments involving gases. Jan Baptist van Helmont is also remembered today largely for his ideas on spontaneous generation and his 5-year tree experiment, as well as being considered the founder of pneumatic chemistry.
Robert Boyle
The Anglo-Irish chemist Robert Boyle (1627–1691) is considered to have initiated the gradual separation of chemistry from alchemy. Although skeptical of elements and convinced of alchemy, Boyle played a key part in elevating the "sacred art" as an independent, fundamental and philosophical discipline. He is best known for Boyle's law, which he presented in 1662, though he was not the first to discover it. The law describes the inversely proportional relationship between the absolute pressure and volume of a gas, if the temperature is kept constant within a closed system. Boyle is also credited for his landmark publication The Sceptical Chymist (1661), which advocated for a rigorous approach to experimentation among chemists. In the work, Boyle questioned some commonly held alchemical theories and argued for practitioners to be more "philosophical" and less commercially focused. He rejected the classical four elements of earth, fire, air, and water, and proposed a mechanistic alternative of atoms and chemical reactions that could be subject to rigorous experiment. Boyle also tried to purify chemicals to obtain reproducible reactions. He was a vocal proponent of the mechanical philosophy proposed by René Descartes to explain and quantify the physical properties and interactions of material substances. Boyle was an atomist, but favoured the word corpuscle over atoms. He commented that the finest division of matter where the properties are retained is at the level of corpuscles. Boyle repeated the tree experiment of van Helmont, and was the first to use indicators which changed colors with acidity. He also performed numerous investigations with an air pump, and noted that the mercury fell as air was pumped out. He also observed that pumping the air out of a container would extinguish a flame and kill small animals placed inside. Through his works, Boyle helped to lay the foundations for the chemical revolution two centuries later.
Development and dismantling of phlogiston
In 1702, German chemist Georg Stahl coined the name "phlogiston" for the substance believed to be released in the process of burning. Around 1735, Swedish chemist Georg Brandt analyzed a dark blue pigment found in copper ore. Brandt demonstrated that the pigment contained a new element, later named cobalt. In 1751, a Swedish chemist and pupil of Stahl's named Axel Fredrik Cronstedt, identified an impurity in copper ore as a separate metallic element, which he named nickel. Cronstedt is one of the founders of modern mineralogy. Cronstedt also discovered the mineral scheelite in 1751, which he named tungsten, meaning "heavy stone" in Swedish. In 1754, Scottish chemist Joseph Black isolated carbon dioxide, which he called "fixed air". In 1757, Louis Claude Cadet de Gassicourt, while investigating arsenic compounds, creates Cadet's fuming liquid, later discovered to be cacodyl oxide, considered to be the first synthetic organometallic compound. In 1758, Joseph Black formulated the concept of latent heat to explain the thermochemistry of phase changes. In 1766, English chemist Henry Cavendish isolated hydrogen, which he called "inflammable air". Cavendish discovered hydrogen as a colorless, odourless gas that burns and can form an explosive mixture with air, and published a paper on the production of water by burning inflammable air (that is, hydrogen) in dephlogisticated air (now known to be oxygen), the latter a constituent of atmospheric air (phlogiston theory). In 1773, Swedish German chemist Carl Wilhelm Scheele discovered oxygen, which he called "fire air", but did not immediately publish his achievement. In 1774, English chemist Joseph Priestley independently isolated oxygen in its gaseous state, calling it "dephlogisticated air", and published his work before Scheele. During his lifetime, Priestley's considerable scientific reputation rested on his invention of soda water, his writings on electricity, and his discovery of several "airs" (gases), the most famous being what Priestley dubbed "dephlogisticated air" (oxygen). However, Priestley's determination to defend phlogiston theory and to reject what would become the chemical revolution eventually left him isolated within the scientific community. In 1781, Carl Wilhelm Scheele discovered that a new acid, tungstic acid, could be made from Cronstedt's scheelite (at the time named tungsten). Scheele and Torbern Bergman suggested that it might be possible to obtain a new metal by reducing this acid. In 1783, José and Fausto Elhuyar found an acid made from wolframite that was identical to tungstic acid. Later that year, in Spain, the brothers succeeded in isolating the metal now known as tungsten by reduction of this acid with charcoal, and they are credited with the discovery of the element.
Volta and the Voltaic pile
Italian physicist Alessandro Volta constructed a device for accumulating a large charge by a series of inductions and groundings. He investigated the 1780s discovery "animal electricity" by Luigi Galvani, and found that the electric current was generated from the contact of dissimilar metals, and that the frog leg was only acting as a detector. Volta demonstrated in 1794 that when two metals and brine-soaked cloth or cardboard are arranged in a circuit they produce an electric current. In 1800, Volta stacked several pairs of alternating copper (or silver) and zinc discs (electrodes) separated by cloth or cardboard soaked in brine (electrolyte) to increase the electrolyte conductivity. When the top and bottom contacts were connected by a wire, an electric current flowed through this voltaic pile and the connecting wire. Thus, Volta is credited with constructing the first electrical battery to produce electricity. Thus, Volta is considered to be the founder of the discipline of electrochemistry. A Galvanic cell (or voltaic cell) is an electrochemical cell that derives electrical energy from a spontaneous redox reaction taking place within the cell. It generally consists of two different metals connected by a salt bridge, or individual half-cells separated by a porous membrane.
Antoine-Laurent de Lavoisier
Antoine-Laurent de Lavoisier demonstrated with careful measurements that transmutation of water to earth was not possible, but that the sediment observed from boiling water came from the container. He burnt phosphorus and sulfur in air, and proved that the products weighed more than the original samples, with the mass gained being lost from the air. Thus, in 1789, he established the Law of Conservation of Mass, which is also called "Lavoisier's Law."
Repeating the experiments of Priestley, he demonstrated that air is composed of two parts, one of which combines with metals to form calxes. In Considérations Générales sur la Nature des Acides (1778), he demonstrated that the "air" responsible for combustion was also the source of acidity. The next year, he named this portion oxygen (Greek for acid-former), and the other azote (Greek for no life). Because of his more thorough characterization of it as an element, Lavoisier thus has a claim to the discovery of oxygen along with Priestley and Scheele. He also discovered that the "inflammable air" discovered by Cavendish – which he termed hydrogen (Greek for water-former) – combined with oxygen to produce a dew, as Priestley had reported, which appeared to be water. In Reflexions sur le Phlogistique (1783), Lavoisier showed the phlogiston theory of combustion to be inconsistent. Mikhail Lomonosov independently established a tradition of chemistry in Russia in the 18th century; he also rejected the phlogiston theory, and anticipated the kinetic theory of gases. Lomonosov regarded heat as a form of motion, and stated the idea of conservation of matter. Lavoisier worked with Claude Louis Berthollet and others to devise a system of chemical nomenclature, which serves as the basis of the modern system of naming chemical compounds. In his Methods of Chemical Nomenclature (1787), Lavoisier invented the system of naming and classification still largely in use today, including names such as sulfuric acid, sulfates, and sulfites. In 1785, Berthollet was the first to introduce the use of chlorine gas as a commercial bleach. In the same year he first determined the elemental composition of the gas ammonia. Berthollet first produced a modern bleaching liquid in 1789 by passing chlorine gas through a solution of sodium carbonate – the result was a weak solution of sodium hypochlorite. Another strong chlorine oxidant and bleach which he investigated and was the first to produce, potassium chlorate (KClO3), is known as Berthollet's Salt. Berthollet is also known for his scientific contributions to the theory of chemical equilibrium via the mechanism of reversible reactions.
Lavoisier's Traité Élémentaire de Chimie (Elementary Treatise of Chemistry, 1789) was the first modern chemical textbook, and presented a unified view of new theories of chemistry, contained a clear statement of the Law of Conservation of Mass, and denied the existence of phlogiston. In addition, it contained a list of elements, or substances that could not be broken down further, which included oxygen, nitrogen, hydrogen, phosphorus, mercury, zinc, and sulfur. His list, however, also included light and caloric, which he believed to be material substances. In the work, Lavoisier underscored the observational basis of his chemistry, stating "I have tried...to arrive at the truth by linking up facts; to suppress as much as possible the use of reasoning, which is often an unreliable instrument which deceives us, in order to follow as much as possible the torch of observation and of experiment." Nevertheless, he believed that the real existence of atoms was philosophically impossible. Lavoisier demonstrated that organisms disassemble and reconstitute atmospheric air in the same manner as a burning body. With Pierre-Simon Laplace, Lavoisier used a calorimeter to estimate the heat evolved per unit of carbon dioxide produced. They found the same ratio for a flame and animals, indicating that animals produced energy by a type of combustion. Lavoisier believed in the radical theory, which stated that radicals, which function as a single group in a chemical reaction, would combine with oxygen in reactions. He believed all acids contained oxygen. He also discovered that diamond is a crystalline form of carbon. Although many of Lavoisier's partners were influential for the advancement of chemistry as a scientific discipline, his wife Marie-Anne Lavoisier was arguably the most influential of them all. Upon their marriage, Mme. Lavoisier began to study chemistry, English, and drawing in order to help her husband in his work either by translating papers into English, a language which Lavoisier did not know, or by keeping records and drawing the various apparatuses that Lavoisier used in his labs. Through her ability to read and translate articles from Britain for her husband, Lavoisier had access to knowledge of many of the chemical advances happening outside of his lab. Furthermore, Mme. Lavoisier kept records of her husband's work and ensured that his works were published. The first sign of Marie-Anne's true potential as a chemist in Lavoisier's lab came when she was translating a book by the scientist Richard Kirwan. While translating, she stumbled upon and corrected multiple errors. When she presented her translation, along with her notes, to Lavoisier, her contributions led to Lavoisier's refutation of the theory of phlogiston. Lavoisier made many fundamental contributions to the science of chemistry. Following his work, chemistry acquired a strict, quantitative nature, allowing reliable predictions to be made. The revolution in chemistry which he brought about was a result of a conscious effort to fit all experiments into the framework of a single theory. He established the consistent use of chemical balance, used oxygen to overthrow the phlogiston theory, and developed a new system of chemical nomenclature. Further potential contributions were cut short when Lavoisier was beheaded during the French Revolution.
19th century Throughout the 19th century, chemistry was divided between those who followed the atomic theory of John Dalton and the energeticists, such as Wilhelm Ostwald and Ernst Mach. Although such proponents of the atomic theory as Amedeo Avogadro and Ludwig Boltzmann made great advances in explaining the behavior of gases, this dispute was not finally settled until Jean Perrin's experimental investigation of Einstein's atomic explanation of Brownian motion in the first decade of the 20th century. Well before the dispute had been settled, many had already applied the concept of atomism to chemistry. A major example was the ion theory of Svante Arrhenius which anticipated ideas about atomic substructure that did not fully develop until the 20th century. Michael Faraday was another early worker, whose major contribution to chemistry was electrochemistry, in which (among other things) a certain quantity of electricity during electrolysis or electrodeposition of metals was shown to be associated with certain quantities of chemical elements, and fixed quantities of the elements therefore with each other, in specific ratios. These findings, like those of Dalton's combining ratios, were early clues to the atomic nature of matter.
John Dalton
In 1803, English meteorologist and chemist John Dalton proposed Dalton's law, which describes the relationship between the components in a mixture of gases and the relative pressure each contributes to that of the overall mixture. Discovered in 1801, this concept is also known as Dalton's law of partial pressures. Dalton also proposed a modern atomic theory in 1803 which stated that all matter was composed of small indivisible particles termed atoms, atoms of a given element possess unique characteristics and weight, and three types of atoms exist: simple (elements), compound (simple molecules), and complex (complex molecules). In 1808, Dalton first published New System of Chemical Philosophy (1808–1827), in which he outlined the first modern scientific description of the atomic theory. This work identified chemical elements as a specific type of atom, therefore rejecting Newton's theory of chemical affinities. Instead, Dalton inferred proportions of elements in compounds by taking ratios of the weights of reactants, setting the atomic weight of hydrogen to be identically one. Following Jeremias Benjamin Richter (known for introducing the term stoichiometry), he proposed that chemical elements combine in integral ratios. This is known as the law of multiple proportions or Dalton's law, and Dalton included a clear description of the law in his New System of Chemical Philosophy. The law of multiple proportions is one of the basic laws of stoichiometry used to establish the atomic theory. Despite the importance of the work as the first view of atoms as physically real entities and the introduction of a system of chemical symbols, New System of Chemical Philosophy devoted almost as much space to the caloric theory as to atomism. French chemist Joseph Proust proposed the law of definite proportions, which states that elements always combine in small, whole number ratios to form compounds, based on several experiments conducted between 1797 and 1804. Along with the law of multiple proportions, the law of definite proportions forms the basis of stoichiometry. The law of definite proportions and constant composition do not prove that atoms exist, but they are difficult to explain without assuming that chemical compounds are formed when atoms combine in constant proportions.
Jöns Jacob Berzelius
A Swedish chemist and disciple of Dalton, Jöns Jacob Berzelius embarked on a systematic program to try to make accurate and precise quantitative measurements and to ensure the purity of chemicals. Along with Lavoisier, Boyle, and Dalton, Berzelius is known as the father of modern chemistry. In 1828 he compiled a table of relative atomic weights, where oxygen was used as a standard, with its weight set at 100, and which included all of the elements known at the time. This work provided evidence in favor of Dalton's atomic theory – that inorganic chemical compounds are composed of atoms combined in whole number amounts. He determined the exact elementary constituents of a large number of compounds; the results strongly supported Proust's Law of Definite Proportions. In discovering that atomic weights are not integer multiples of the weight of hydrogen, Berzelius also disproved Prout's hypothesis that elements are built up from atoms of hydrogen. Motivated by his extensive atomic weight determinations and in a desire to aid his experiments, he introduced the classical system of chemical symbols and notation with his 1808 publication Lärbok i Kemien, in which elements are abbreviated to one or two letters to make a distinct symbol from their Latin name. This system of chemical notation—in which the elements were given simple written labels, such as O for oxygen, or Fe for iron, with proportions denoted by numbers—is the same basic system used today. The only difference is that instead of the subscript number used today (e.g., H2O), Berzelius used a superscript (H2O). Berzelius is credited with identifying the chemical elements silicon, selenium, thorium, and cerium. Students working in Berzelius's laboratory also discovered lithium and vanadium. Berzelius developed the radical theory of chemical combination, which holds that reactions occur as stable groups of atoms called radicals are exchanged between molecules. He believed that salts are compounds formed of acids and bases, and discovered that the anions in acids were attracted to a positive electrode (the anode), whereas the cations in a base were attracted to a negative electrode (the cathode). Berzelius did not believe in the Vitalism Theory, but instead in a regulative force which produced organization of tissues in an organism. Berzelius is also credited with originating the chemical terms "catalysis", "polymer", "isomer", and "allotrope", although his original definitions differ dramatically from modern usage. For example, he coined the term "polymer" in 1833 to describe organic compounds which shared identical empirical formulas but which differed in overall molecular weight, the larger of the compounds being described as "polymers" of the smallest. By this long-superseded, pre-structural definition, glucose (C6H12O6) was viewed as a polymer of formaldehyde (CH2O).
New elements and gas laws
English chemist Humphry Davy was a pioneer in the field of electrolysis, using Alessandro Volta's voltaic pile to split up common compounds and thus isolate a series of new elements. He went on to electrolyse molten salts and discovered several new metals, especially sodium and potassium, highly reactive elements known as the alkali metals. Potassium, the first metal that was isolated by electrolysis, was discovered in 1807 by Davy, who derived it from caustic potash (KOH). Before the 19th century, no distinction was made between potassium and sodium. Sodium was first isolated by Davy in the same year by passing an electric current through molten sodium hydroxide (NaOH). When Davy heard that Berzelius and Pontin prepared calcium amalgam by electrolyzing lime in mercury, he tried it himself. Davy was successful, and discovered calcium in 1808 by electrolyzing a mixture of lime and mercuric oxide. He worked with electrolysis throughout his life and, in 1808, he isolated magnesium, strontium and barium. Davy also experimented with gases by inhaling them. This experimental procedure nearly proved fatal on several occasions, but led to the discovery of the unusual effects of nitrous oxide, which came to be known as laughing gas. Chlorine was discovered in 1774 by Swedish chemist Carl Wilhelm Scheele, who called it "dephlogisticated marine acid" (see phlogiston theory) and mistakenly thought it contained oxygen. Scheele observed several properties of chlorine gas, such as its bleaching effect on litmus, its deadly effect on insects, its yellow-green colour, and the similarity of its smell to that of aqua regia. However, Scheele was unable to publish his findings at the time. In 1810, chlorine was given its current name by Humphry Davy (derived from the Greek word for green), who insisted that chlorine was in fact an element. He also showed that oxygen could not be obtained from the substance known as oxymuriatic acid (HCl solution). This discovery overturned Lavoisier's definition of acids as compounds of oxygen. Davy was a popular lecturer and able experimenter.
French chemist Joseph Louis Gay-Lussac shared the interest of Lavoisier and others in the quantitative study of the properties of gases. From his first major program of research in 1801–1802, he concluded that equal volumes of all gases expand equally with the same increase in temperature: this conclusion is usually called "Charles's law", as Gay-Lussac gave credit to Jacques Charles, who had arrived at nearly the same conclusion in the 1780s but had not published it. The law was independently discovered by British natural philosopher John Dalton by 1801, although Dalton's description was less thorough than Gay-Lussac's. In 180