/kloc-cavendish, an English chemist in the 0/8th century.
Cavendish is a millionaire, but his life is very simple. He built a large-scale laboratory at home with his own money and devoted his life to scientific research. A historian of science once said: cavendish "is the richest among the learned and the most learned among the rich." He has a keen observation of things and is good at experimental design. His experimental results are quite accurate, and his research scope is very wide. He made important discoveries in many chemical, mechanical and electrical problems and in the study of the average density of the earth. But he believed in phlogiston, which made him take some detours in chemical research. In the past 50 years, he has only published 18 papers, all of which are experimental and observational except one which is theoretical. After his death, it was found that he wrote a lot of valuable papers, but they were not published. These manuscripts of his are precious documents of scientific research, which were later compiled and published by physicist Maxwell and chemist Thorpe respectively.
There is an interesting story about these papers in the history of chemistry. Cavendish did an experiment in 1785. He let an electric spark pass through the mixture of ordinary air and oxygen, trying to oxidize all the nitrogen in it, and the nitrogen dioxide produced was absorbed by caustic potash. The experiment was done for three weeks, and finally there was a small bubble that could not be oxidized. His experimental records are kept in the manuscript, which reads: "The polluted air in the air is not a single substance (nitrogen), and there is another polluted air that is not combined with defluorinated air (oxygen), and the total amount does not exceed112. More than one hundred years later, 65,438+0,892, a physicist at Cambridge University, England. L.1842-1919), it is puzzling that the nitrogen obtained from the air is 0.0064 g per liter heavier than the nitrogen produced by ammoxidation. Chemist Ramsay (W.1852-1916) thinks that nitrogen in the air can contain heavier unknown gases. At this time, the chemistry professor Dewar (J. 1842- 1923) mentioned to them the above experiment of Cavendish, a doyen of Cambridge University, and the mystery of small bubbles. They immediately borrowed Cavendish's scientific data to read, and Rayleigh repeated Cavendish's experiment that year, and soon got a small bubble. Ramsar designed a new experiment. After removing water vapor, carbonic acid gas, oxygen and nitrogen from the air, this gas is also obtained, and its density is higher than that of nitrogen. It is proved by spectroscopic examination that it is a new element named argon. In this way, Cavendish's work in that year played an important role in the discovery of argon in 1894. From this story, we can see Cavendish's rigorous scientific research style and his great contribution to chemistry. 187 1 year, Cambridge university established a physics laboratory named after Cavendish. This is the famous Cavendish laboratory, which has been an important research center of modern physics in the world for decades.
The discovery of hydrogen and its properties.
Before the end of 18, many people had done experiments to make hydrogen, so it is hard to say who discovered hydrogen. Even cavendish, who has made great contributions to the discovery and research of hydrogen, thinks that the discovery of hydrogen is not only his credit. As early as16th century, the famous Swiss doctor's palace described that iron filings would produce a gas when they came into contact with acid. /kloc-in the 7th century, Helmont (J.B. 1579- 1644), a famous Belgian medical chemist, accidentally came into contact with this gas, but failed to separate and collect it.
Although Boyle collected this gas by accident, he didn't study it. They only know that it is flammable and know little about it. 1700, French pharmacist Lhemery (n.1645-1715) was also mentioned in the report of the Paris Academy of Sciences. It was cavendish who first collected hydrogen and studied its properties carefully.
1766, cavendish submitted a research report "Artificial Air Experiment" to the Royal Society, which described that he made "combustible air" (i.e. hydrogen) by reacting iron and zinc with dilute sulfuric acid and dilute hydrochloric acid, and collected it for research by the drainage gas collection method invented by priestley. He found that a certain amount of a metal reacts with a sufficient amount of various acids, and the amount of this gas produced is fixed, regardless of the type and concentration of the acid. He also found that when hydrogen is mixed with air and ignited, it will explode; It is also found that hydrogen combines with oxygen to form water, thus realizing that this gas is different from other known gases. However, because he is a devout believer in phlogiston theory, according to his understanding: this gas burns so violently that it is bound to be rich in phlogiston; Sulfur turns into sulfuric acid after combustion, so there is no phlogiston in sulfuric acid; According to phlogiston, metals also contain phlogiston. So he thinks that this gas is decomposed by metal, not by acid. He imagined that when metal was dissolved in acid, "the phlogiston contained in it was released, and this combustible air was formed". He even assumed that hydrogen was phlogiston at one time, which was quickly endorsed by some outstanding chemists at that time, such as Scheler and Kilwan (Kirwan, R.1735-1812). Because the bladder balloon is filled with hydrogen, the balloon will rise slowly. This phenomenon is used by some believers of phlogiston theory as the basis of their "argument" that phlogiston has negative weight. But cavendish is an extraordinary scientist after all. Later, he calculated the buoyancy of the balloon in the air. Through accurate research, it is proved that hydrogen has weight, but it is much lighter than air. The experiment he did was as follows: first, weigh the metal and the flask containing acid, then put the metal into the acid, collect hydrogen by drainage gas collection method and measure the volume, and then weigh the total amount of the flask and its contents after the reaction. In this way, he determined that the proportion of hydrogen is only 9% of that of air. But these chemists still refuse to give up the old theory easily. In view of the fact that hydrogen will produce water after burning, they say that hydrogen is a compound of phlogiston and water.
The synthesis of water denies the wrong view that water is an element. In ancient Greece, empedocles proposed that there are only four elements in the universe: fire, air, water and earth, which make up everything. From then until the 1970s, people always thought that water was an element. 178 1 year, priestley put hydrogen and air into a closed glass bottle and detonated it with an electric spark. Dewdrops appeared on the inner wall of the bottle In the same year, cavendish also repeated the experiment with a mixture of hydrogen and air in different proportions, confirming that the dew is pure water, indicating that hydrogen is a component of water. At this time, oxygen has been discovered. cavendish used pure oxygen instead of air to carry out experiments, which not only proved that hydrogen and oxidation synthesized water, but also confirmed that about 2 parts by volume of hydrogen and 1 part by volume of oxygen just synthesized water (published in 1784). These experimental results undoubtedly prove that water is a compound of hydrogen and oxygen, not an element, but cavendish, like priestley, still insists that water is an element, oxygen is water without phlogiston, and hydrogen is water with excessive phlogiston. He expressed the combustion of "combustible air" (hydrogen) with the following formula:
(water+phlogiston)+(water-phlogiston)-→ water
Combustible air (hydrogen) burns in air (oxygen).
1782, lavoisier repeated their experiment, using a red-hot barrel to decompose water vapor. Only then did the correct conclusion be clearly put forward: water is not an element, but a hydroxide compound, which corrected the wrong concept of taking water as an element for more than two thousand years. 1787, he named this gas "h-hydrogene", which means "producing water", and confirmed that it was an element.