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MOST IMPORTANT SCIENTIFIC DISCOVERIES
Theory of combustion. History and essence of scientific discovery
Directory / The most important scientific discoveries In the second half of the XNUMXth century, chemistry was on the rise - discoveries poured in after discoveries. At this time, a number of brilliant experimenters came to the fore - Priestley, Black, Scheele, Cavendish and others. In the works of Black, Cavendish, and especially Priestley, a new world opens up to scientists - the region of gases, hitherto completely unknown. Research methods are constantly being improved. Black, Cronstedt, Bergman and others develop qualitative analysis. As a result, it was possible to discover a mass of new elements and compounds. At the turn of the 1659th and 1734th centuries, the German chemist Georg Ernst Stahl (XNUMX–XNUMX) proposed the so-called phlogiston theory—essentially the first chemical theory. Although it turned out to be erroneous, it made it possible to systematize the processes of combustion and roasting (calcination) of metals, explaining these processes from a unified point of view. Steel believed that various substances and metals contain in their composition a special "combustibility principle" - phlogiston. When calcined, the metals lost phlogiston, turning into oxides, i.e., the oxidation processes consisted in the loss of phlogiston by the oxidizing substances. On the contrary, in the course of reduction processes, the oxides acquired phlogiston, becoming metals again. Criticism of the doctrine of phlogiston greatly contributed to the development of chemical thinking. However, the main phenomena of chemistry - the processes of combustion and oxidation in general, the composition of air, the role of oxygen, the structure of the main groups of chemical compounds (oxides, acids, salts, etc.) - have not yet been explained. On the contrary, facts accumulated and ideas became confused. Rather plausible in the presentation of Stahl, the doctrine of phlogiston turns into some kind of phlogiston among his followers: this is no longer one theory, these are dozens of theories, confusing, contradictory, changing with each author. In the middle of the XNUMXth century, the so-called pneumatic chemistry, which studied gases from a chemical point of view, came to the fore. One of her outstanding achievements was the discovery of oxygen. Understanding its nature as an independent gaseous chemical element allowed the Frenchman Antoine Lavoisier debunk the concept of phlogiston and formulate the oxygen theory of combustion. Together with major achievements in chemical analysis, this event marked the beginning of the first chemical revolution. Antoine Laurent Lavoisier (1743–1794) was born to a lawyer on August 28, 1743. He received his early education at the Mazarin College. Antoine was an excellent student. After leaving college, he entered the Faculty of Law. In 1763, Antoine received a bachelor's degree, the next year - a license in law. But the legal sciences could not satisfy his boundless and insatiable curiosity. Without leaving his studies in law, he studied mathematics and astronomy with Lacaille, a very famous astronomer at that time, who had a small observatory at the Mazarin College; botany - with the great Bernard Jussier, with whom he compiled herbariums; mineralogy - from Guetard, who compiled the first mineralogical map of France; chemistry - at Ruel. The first works of Lavoisier were made under the influence of his teacher and friend Guetard. Gaetar undertook a number of excursions; Lavoisier was his collaborator for three years, beginning in 1763. The fruit of this excursion was his first work - "Investigation of various types of gypsum". After five years of collaboration with Guetard, in 1768, when Lavoisier was 25 years old, he was elected a member of the Academy of Sciences. In life, Lavoisier adhered to a strict order. He made it a rule to study science for six hours a day: from six to nine in the morning and from seven to ten in the evening. The rest of the day was divided between occupations, academic affairs, work in various commissions, and so on. One day a week was devoted exclusively to science. In the morning, Lavoisier locked himself in the laboratory with his collaborators; here they repeated experiments, discussed chemical questions, argued about the new system. Here one could see the most glorious scientists of that time - Laplace, Monge, Lagrange, Giton Morvo, Macker. Lavoisier's laboratory became the center of contemporary science. He spent huge sums on the purchase and installation of instruments, representing in this respect the exact opposite of some of his contemporaries. At that time, the basic law of chemistry, the guiding rule of chemical research, had yet to be found; create a method of research that follows from this basic law; to explain the main categories of chemical phenomena and, finally, to debunk the existing fantastic theories. This task was undertaken and carried out by Lavoisier. Experimental talent was not enough to carry it out. It was required to attach a golden head to the golden hands. Such a happy union represented Lavoisier. In scientific activity, Lavoisier is struck by its strictly logical course. First, he develops a research method. Then the scientist puts the experiment. So, for 101 days he distilled water in a closed apparatus. The water evaporated, cooled, returned to the receiver, evaporated again, and so on. The result was a significant amount of sediment. Where did he come from? The total weight of the apparatus at the end of the experiment did not change: it means that no substance was added from the outside. In the course of this work, Lavoisier is convinced of the omnipotence of his method - the method of quantitative research. Having mastered the method to perfection, Lavoisier proceeds to his main task. His works, which created modern chemistry, cover the period from 1772 to 1789. The starting point of his research was the fact of an increase in the weight of bodies during combustion. In 1772, he submitted a short note to the academy, in which he reported the result of his experiments, which showed that when sulfur and phosphorus are burned, they increase in weight due to air, in other words, they combine with part of the air. This fact is the main, capital discovery of the phenomenon, which served as the key to explaining all the others. No one understood this, and at first glance it may seem to the modern reader that we are talking about a single, unimportant phenomenon ... But this is not true. To explain the fact of combustion meant to explain the whole world of oxidation phenomena occurring always and everywhere in the air, earth, organisms - in all dead and living nature, in countless variations and diverse forms. About sixty memoirs were devoted to the elucidation of various questions connected with this starting point. In them, the new science develops like a ball. Combustion phenomena naturally lead Lavoisier, on the one hand, to the study of the composition of air, and, on the other hand, to the study of other forms of oxidation; to the formation of various oxides and acids and the understanding of their composition; to the process of respiration, and hence to the study of organic bodies and the discovery of organic analysis, etc. Lavoisier's immediate task was the theory of combustion and the related question of the composition of air. In 1774, he presented to the Academy a memoir on calcining tin, in which he formulated and proved his views on combustion. Tin was calcined in a closed retort and turned into "earth" (oxide). The total weight remained unchanged - therefore, the increase in the weight of tin could not occur due to the addition of "fiery matter", penetrating, as believed Boylethrough the walls of the vessel. The weight of the metal has increased. This increase is equal to the weight of that part of the air that disappeared during calcination. It turns out that the metal, turning into earth, combines with air. This is the end of the oxidation process: no phlogistons, "fiery matters" are involved here. In a given volume of air, only a certain amount of metal can burn, and a certain amount of air disappears. From this follows the idea of its complexity: “As you can see, part of the air is capable of forming earths when combined with metals, while the other is not; this circumstance makes me assume that air is not a simple substance, as was previously thought, but consists of very different substances. ". The following year, 1775, Lavoisier presented a memoir to the academy, in which the composition of air was for the first time precisely clarified. Air consists of two gases, "pure air", capable of intensifying combustion and respiration, oxidizing metals, and "mephitic air", which does not have these properties. The names oxygen and nitrogen were given later. Let us delve into the course of Lavoisier's reasoning. The metal increases in weight - it means that some substance has joined it. Where did it come from? We determine the weight of other bodies involved in the reaction, and we see that the air has decreased in weight by the same amount as the weight of the metal has increased; therefore, the desired substance was released from the air. This is a method of weight determination. However, in order to understand its meaning, it must be recognized that all chemical bodies have weight, that a weighty body cannot become weightless, and finally, not a single particle of matter can disappear or arise from nothing. In the same memoir, Lavoisier elucidated the structure of "permanent air," as carbon dioxide was then called. If mercury oxide is heated in the presence of coal, the liberated oxygen combines with coal, forming "permanent air". In the treatise On Combustion in General (1777), he develops his theory in detail. All combustion is the union of a body with oxygen; its result is a complex body, namely "metal earth" (oxide) or acid (anhydride in modern terminology). The theory of combustion led to an explanation of the composition of various chemical compounds. Oxides, acids and salts have long been distinguished, but their structure remained mysterious. Their general result can be formulated as follows: Lavoisier gave the first scientific system of chemical compounds, establishing three main groups - oxides (compounds of metals with oxygen), acids (compounds of non-metallic bodies with oxygen) and salts (compounds of oxides and acids). Ten years have passed since the first work of Lavoisier, and he almost did not touch on the theory of phlogiston. He just managed without her. The processes of combustion, respiration, oxidation, the composition of air, carbon dioxide, and many other compounds were explained without any mysterious principles quite simply and clearly - by the connection and separation of real weight bodies. But the old theory still existed and influenced scientists. In 1783, Lavoisier published Meditations on Phlogiston. Based on his discoveries, he proves the complete uselessness of the phlogiston theory. Without it, the facts are explained clearly and simply; with it, endless confusion begins. "The chemists have made of phlogiston a nebulous principle, which is not at all precisely defined and therefore suitable for all sorts of explanations, sometimes it is a weighty principle, sometimes weightless, sometimes free fire, sometimes fire connected with the earth; sometimes it passes through the pores of vessels ", sometimes they are impenetrable to him; he explains at once both alkalinity and non-alkalinity, and transparency and dullness, and colors and the absence of colors. This is a real Proteus, which changes shape every minute." "Reflections on Phlogiston" was a kind of funeral march for the old theory, since it could have long been considered buried. Finally, knowledge of hydrogen and its oxidation product enabled Lavoisier to lay the foundation stone for organic chemistry. He determined the composition of organic bodies and created organic analysis by burning carbon and hydrogen in a certain amount of oxygen. According to N. Menshutkin: "Thus, the history of organic chemistry, like that of inorganic chemistry, has to begin with Lavoisier." Author: Samin D.K.
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