Ancient Period
This period covers from primitive man through the ancient civilizations of China, India and Greece and their contemporaries up to 350 BC.
The first people who began to use instruments made use of nature as it was. For example, stones, tree branches or animal bones could be used as valuable tools. However, nature also modified things, for example meat obtained through hunting could start to smell bad and decompose, as could fruit juices, which in time could be converted into other types of beverages.
These types of alterations that occur in nature and that are accompanied by a fundamental change in its structure are the object of study of what we now call chemistry.
With the conquest of fire, man learns to extract and work metals, thus deliberately benefiting from some of the transformations that the elements undergo with heat. Some of the first metals used by man were copper and gold, which were certainly found in their free state in nature, and which have a distinctive property: they are malleable; that is, they can be flattened and formed into sheets without breaking, as is the case with stones, which pulverize, and wood, which splinters and splits.
Men realized that copper could be endowed with a cutting edge, like that of stone tools, but its edge would hold longer than that of stone tools. Only the lack of free copper in nature prevented its widespread use.
Copper became more abundant when it was discovered that it could be obtained from bluestones. How these discoveries were made we will probably never know. But it may have occurred some 4,000 B.C. in the Sinai Peninsula or in the mountainous areas east of Samaria, what is now Iran. This metal was used in tool making in the more developed centers of civilization. In the third millennium B.C., it was discovered that by mixing tin with copper a new metal was formed; this alloy (the name given to the union of metals) was called bronze, and by 2000 B.C. it was common enough to be used in the manufacture of weapons and armor. After the Bronze Age came another important discovery, a harder metal: iron. Unfortunately this mineral was too scarce, at first the only sources of iron were pieces of meteorites, which were too rare to find. Moreover, up to that time, there was no procedure for extracting it from stones, since more intense heat was required to melt iron than to melt copper.
The secret of iron smelting was unveiled in the far east of Asia Minor around 1,500 B.C. The Hittites, who had built an empire in that region, were the first to use it to make tools. Pure iron (wrought iron) is not very hard; however, its hardness was improved by mixing it with a sufficient amount of carbon, forming an alloy with this metal, which we know as steel.
By 800 B.C., the chemical arts were well developed. This was particularly true in Egypt, where they excelled especially in the extraction of metals such as copper, lead, iron, gold and silver; in addition, the priests were very interested in methods of embalming and preserving the human body after death.
They were not only expert metallurgists, but also worked with extraordinary skill with mineral pigments and vegetable infusions. Masters in the manufacture of glass and ceramics, they applied the biochemical process of fermentation to the manufacture of bread and beer. We must emphasize that the practices of all these procedures were developed as an art and not as a science.
We cannot forget that the practices of the chemical arts were also developed in China and India, especially in the work of pyrotechnics, the work of fabrics and perfumes.
Greece (650 B.C. and 380 B.C.)
Greek philosophers were more interested in seeking a rational explanation for the origin of the universe. One of the themes they developed was the divisibility of matter.
In the 5th century BC, Leucippus was the first to question the indivisibility of matter, since he supposed that if matter is divided into infinite parts, it would reach a point where matter would be so small that it could no longer be divided. Democritus, a disciple of the previous one, called this particle atom. He also assumed that the atoms of each element were different and gave matter different properties.
During the years 383-322 BC, a group of philosophers, including Aristotle of Stagira, did not accept the atomistic idea.
He accepted the idea of the four elements. The idea was based on the existence of four fundamental properties: hot, wet, cold and dry. The combination of these properties gives rise to the four elements or simple bodies: earth, air, fire and water.
He established that all substances were composed of these four elements in different proportions.
Period of alchemy (350 B.C-1500 A.D.)
This period in the history of chemistry in Europe is practically a “dark age”, since the maintenance and extension of alchemy was in the hands of the Arabs for five centuries. Some terms derived from Arabic still remain: alkali, alembic, alcohol, carboy, zircon, naphtha.
The most important alchemist was Jabir ibn-Hayyan, later known in Europe as Geber. Among many contributions, he described ammonium chloride and taught how to prepare albayalde (lead carbonate), distilled acetic acid from vinegar.
However, the most important objective of this period was the contribution related to the transmutation of metals, which consisted in the pretension of the transformation of metals into gold. He considered mercury to be the metal par excellence and on the other hand sulfur possessed the property of being combustible. Jabir believed that metals were formed by mixtures of mercury and sulfur; therefore, it was only necessary to find some material that would facilitate the combination of mercury and sulfur as well as the exact proportion to form gold.
This activating substance for the Greeks was xerion, which means “dry”. The Arabs called it al-iksir, and in Europe it eventually became “elixir”, commonly called “philosopher’s stone”. This powerful elixir had other properties such as curing all diseases and granting immortality, hence it was called the “elixir of life”. It was this idea that took shape as the period of iatrochemistry.
The early alchemists made many important contributions. For example, they developed a system for attaching symbols to the substances they used, and even though they are very different from those used today, this was the beginning of the chemical symbology we use today.
During the 17th century, alchemy went into decline, and in the 18th century it was transformed into what we know today as chemistry.
The Phlogiston (1650-1774)
From 1650 onwards, when fire began to be applied in steam engines, it also led men to take a greater interest in this phenomenon and its possible new applications.
Within this field, chemists began to concern themselves more deeply with the subject of combustion. According to Greek conceptions, everything that burns contains fire, which under certain conditions is capable of being released.
To explain this phenomenon, Georg Ernest Stahl proposed a theory for the flammability of bodies that he called phlogiston (“to make burn”). Stahl’s proposal was that all combustible bodies lost something when they burned: phlogiston; at the same time there remained a residue, known as ash or “lime” (now oxide), which lacked phlogiston and therefore could not continue to burn.
Likewise, the phlogiston theory was also applicable, according to Stahl, to the molding of metals, which for him was equivalent to the combustion of wood; he affirmed that metals contained phlogiston, but not when they were moldy.
This idea was important because it made it possible to propose an explanation for the conversion of some minerals into metal. According to the phlogisists, when a mineral is heated with a substance very rich in phlogiston, as in the case of charcoal, it passes from the charcoal to the mineral, transforming the charcoal into ash (lime), a substance poor in phlogiston, while the opposite happens with the mineral.
There was, however, a phenomenon that neither Stahl nor his disciples were able to solve. As we have analyzed, bodies that burn, such as wood or paper, seemed to be consumed to a large extent when they entered into combustion, leaving a residue (ashes) that was much lighter than the original body. This situation is consistent with the explanation for the release of phlogiston. However, when metals became moldy they also released phlogiston, but when the metal became moldy it increased in mass.
This contradiction and unsolved problem did not seem so important at the time, since the chemists of the time did not attach importance to precise measurements. Therefore, mass variations could be ignored. After almost a hundred years the phlogiston theory was losing strength and credibility. One of the significant events was the discovery of carbon dioxide by Joseph Black.
Modern Period (1774 to the present day)
Modern chemistry began with the investigation of gases under vacuum and various pressures by Torricelli, Blaise Pascal, Robert Boyle in the 18th century.
In 1772, a French nobleman named Antoine Laurent Lavoisier (1774-1794) began experimenting with combustion and introduced the balance to determine the masses of substances before and after the process.
Lavoisier rejected the phlogiston theory and proposed instead that when a substance burns it is associated with oxygen in the air. In addition, he introduced quantitative and not only qualitative measurement to experimentation in modern chemistry.
In 1789, Lavoisier published his “Traité élémentaire de chimie”, which was the first modern chemistry text. It included a list of all the elements, or rather, of all the substances he considered to be elements. It should be noted that of the thirty-three substances named only two were totally wrong. These were “light” and “caloric” which, as later became evident, were not substances, but forms of energy. Of the remaining thirty-one elements, some were true elements and others were compounds that could be decomposed into simpler substances.
In the same year that his book was published, the French Revolution triumphed, quickly degenerating into ferocious excesses of terror. Lavoisier was unfortunately one of the victims of the guillotine. Thus, in 1794, one of the greatest chemists who ever lived passed away.
For all these contributions to the development of science he is now universally remembered as the “father of chemistry”.
The scientific method
Chemistry, like other sciences such as physics and biology, uses empirical or experimental methods to better understand some phenomena that occur in nature. This seems to us a logical and indispensable practice today. But before the 17th century, it was not a common process.
Although scientists may analyze a situation from different points of view when faced with the same problem, they do so by following some common guidelines that have acquired the name “scientific method”. This method is a general approach that can be summarized in the following scheme.
This process is very dynamic, as it allows new hypotheses to be put forward. If the experimentation does not prove the hypothesis, we start from the beginning making another series of observations that will lead to the formulation of new hypotheses, as well as new experimental designs can be carried out until the hypotheses are proved. The hypotheses that resist experimental tests and prove to be useful to explain and predict behavior are called theories.
