Scheler found that chlorine made an important contribution to chemistry. /kloc-in the late 8th century, due to the development of metallurgical industry, various ores were studied. One of them is pyrolusite. After three years of hard work, Scheler determined that it was a new metal oxide. According to the statement at that time, this is a "new metal for dephosphorization", and Scheler named this metal manganese. Scheler discovered chlorine in his research on this pyrolusite. Pyrolusite is insoluble in dilute sulfuric acid and nitric acid, but soluble in hydrochloric acid, and immediately emits suffocating yellow-green gas, similar to the gas produced when aqua regia is heated, which makes people's lungs extremely uncomfortable. He did various experiments with this gas and found that it was slightly soluble in water, which made the water slightly sour. With bleaching function, it can make blue paper almost white, and can also bleach colored flowers and green leaves; It can also corrode metals; Insects in this gas will die immediately and the fire will be put out immediately. Because he believed in the phlogiston theory, he mistakenly thought that this gas was produced because "manganese dioxide" (manganese dioxide) took phlogiston from hydrochloric acid, so he called it "phlogiston hydrochloric acid" and didn't think it was an element. It is this view that deprived him of the opportunity to know chlorine correctly.

Although Scheler discovered chlorine gas, he also knew some of its properties. It is not clear what kind of gas this is. At this time, French chemist Bertholle continued to study chlorine. He first introduced chlorine into a cold empty glass bottle, so that the acid vapor in the chlorine gas was condensed by cold, and then introduced the chlorine gas from which the acid vapor was removed into three bottles filled with water in turn, so that the chlorine gas was dissolved in water. He found that an aqueous solution in which chlorine gas is dissolved can be decomposed into hydrochloric acid and oxygen where there is light. Toret judged that chlorine is a combination of hydrochloric acid and oxygen;

Chlorine = hydrochloric acid+oxygen

Chlorine is a loose compound of hydrochloric acid and oxygen, so it will decompose when exposed to sunlight. In fact, at that time, people had used many chemicals or other means to treat chlorine gas, but failed to decompose it into hydrochloric acid and oxygen. Bertore's judgment obviously contradicts some other studies. The main reason why he made this wrong judgment is that he ignored the effect of water on chlorine.

1809, chemists Gay-Lussac and Turner (L.J. 1777- 1857) studied the composition of hydrochloric acid by decomposition method. At that time, metallic potassium had been proved to be an element. So they used metal potassium or iron to react with hydrochloric acid gas to see if he could release chlorine gas. After the experimental results came out, they said, "We studied the reaction of metallic potassium to hydrochloric acid gas. At room temperature, this reaction is very slow; However, after potassium melts, it immediately burns in hydrochloric acid gas to produce potassium chloride and hydrogen. "

"The amount of hydrogen collected in this experiment is exactly equal to what happens when potassium comes into contact with water."

"When we are in a dark red high temperature, using hydrochloric acid gas to pass through the scraped iron filings will release a lot of hydrogen without knowing that hydrochloric acid is mixed and ferric chloride is obtained at the same time; The residual iron filings are not oxidized. "

At moderate temperature, hydrochloric acid gas is melted and ground into fine powder by lead monoxide, and hydrogen is collected, but hydrogen has been combined with oxidation and turned into water.

This experiment proves that instead of chlorine decomposing into hydrochloric acid and oxygen, hydrochloric acid decomposes into chlorine and hydrogen.

In the same year, Gay-Lussac and Tanner proved the composition of hydrochloric acid by synthesis. They mix the same amount of hydrogen and chlorine together, let it stand for a few days, or heat it slightly, or expose it to the sun, which can be converted into hydrochloric acid gas.

This experiment strongly proves that hydrochloric acid gas is a compound of hydrogen and chlorine, and it is the only substance formed by the combination of these two gases. The change should be expressed as: chlorine+hydrogen = hydrochloric acid gas.

Gay-Lussac and Tanner's experiments made a correct conclusion about the composition of hydrochloric acid, but chlorine is still a compound in their eyes. Because when French chemist lavoisier put forward the theory of combustion oxidation, he also put forward the argument that "oxygen is an acid-forming element" and thought that all acid components are aerobic, which was deeply imprinted in the chemist's mind. Gay-Lussac and Turner are so convinced of this view that they also believe that chlorine is some kind of "free radical" oxide. Since chlorine is an oxide of a certain group, hydrochloric acid should be a compound of a certain group with oxygen and hydrogen: hydrochloric acid = X (a certain group)+oxygen+hydrogen.

In order to find oxygen in chlorine, chemists tried various methods, such as using metal, red charcoal, phosphorus or other oxygen absorbers, but they did not separate oxygen from chlorine. 18 10, a young British chemist David (S.H. 1778- 1829) used a dry battery to burn charcoal to white heat, but still did not decompose chlorine. After these failures, David began to doubt the idea that chlorine contains oxygen. He redone the experiment of synthesizing hydrochloric acid by Gay-Lussac and Turner, and confirmed that the conclusion of synthesizing hydrochloric acid by hydrogenation of chlorine gas is correct, except for a little water, there are no other impurities. Since there is no oxygen in chlorine or hydrochloric acid, why do we insist on the existence of oxygen? He thinks that all experiments about chlorine can only be reasonably explained when chlorine is considered as an element. In this year's 165438+ 10 month, David read his paper at the Royal Society and formally proposed that chlorine is an element.