History
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Robert Boyle 1627—1691
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Robert Boyle 1627—1691
Robert Boyle was born on January 1st, 1627 in Waterford, Ireland. He emphasized on the importance of conducting experiments in scientific research and was a sci- entist with outstanding experimental skills. He optimized many scientific instru- ments and made contributions to many areas of research. Boyle is regarded as the founder of modern chemistry. He considered chemistry as a physical science, not just a practical art or mysterious alchemy, although he was a believer in alchemy. Through experiments, he proved that the ancient Greek theory of four elements was invalid, and proposed a concept of elements close to the one we have today. He believed that all matters were composed of minute particles and the universe worked like a sophisticated machine. His thoughts deeply influenced many scien- tists including Newton. Boyle died on December 31st, 1691 (aged 64) in London, England. The main scientific contributions of Boyle are:
l Discovery of Boyle’s Law (at constant temperature, the absolute pressure and the volume of a fixed amount of gas are inversely proportional). l Design of a new vacuum pump and conducted experiments inside vacuum, and finding that in vacuum sound could not transmit and a candle could not burn. l Preliminary explanation to combustion and metal calcination. l Emphasis on the importance of chemical analysis, invention of experimental methods to identify chemicals and measure purity, the use of vegetable colors to identify acid and base.
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The drawings on the left show Boyle’s vacuum pump described in New Experiments Physico-Mechanical, Touch the Spring of the Air, and Its Effects published in 1660 (a photorealistic CG reproduction can be found on page 60). Boyle’s got a lot of help from his assistant Robert Hooke for designing and con- structing the pump. The first vacuum pump was invented by Otto von Guericke in 1654. In 1657, von Guericke conducted the famous experiment with the Magdeburg hemispheres, demonstrating the power of atmosphere pressure. Boyle and Hooke made a lot of improvements upon von Guericke’s design, making the pump easy to use. Also, they could conduct experiments inside the pump. Boyle’s vacuum pump is made of a spherical glass globe with a diameter of 38 cm and a brass pumping cylinder connecting with it. The globe has an open- ing on the top. Objects used in experiments can be transferred into the globe through this opening and later sealed by a brass cap and lute. The air pump- ing process is controlled by the valve connecting the pump and globe and a small brass plug on the pump, as shown graphically in the opposite page (please pay attention to the colored component in each step). In New Experiments Physico-Mechanical, Touch the Spring of the Air, and Its Effects, Boyle described 43 experiments, covering physics, chemistry, biology and other subjects. For chemistry, he discovered that a candle and charcoal could not burn inside vacuum, which was the opposite to Boyle’s original hypothesis. Based on the four-element theory, as “gas” was pumped out, “fire” in the inflammable ob- jects should release much easier. After Boyle, many Internal structure scientists tackled the combustion problem and led of the pumping cylinder. to the famous chemical revolution.
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John Mayow 1641—1679
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John Mayow 1641—1679
John Mayow was born in about 1641 in England. Although his research on com- bustion and respiration was more advanced than his peers, few paid attention to his work during his time. There was even some controversy regarding his contribu- tion to chemistry among historians. Today, however, it is accepted that Mayow’s experiments were innovative and well-reasoned. In the October of 1679, Mayow, less than 40 years old, died in London, England. The main scientific contributions of Mayow are:
l finding that combustion and respiration were similar in terms of consuming a part of the air (i.e. oxygen), which he named “nitro-aereus”. l pointing out that “nitro-aereus” entered animal lungs during respiration, and that muscle contraction and body heat were results of chemical reactions be- tween “nitro-aereus” and substances in the body.
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Above are Mayow’s apparatuses for studying combustion described in his Tractatus Quinque Medi- co-Physici published in 1674. He discovered that inside a container sealed by water, a burning candle (left) and combustion of inflammable substance ignited by fire glass both consumed a portion of the air, leading to the increase of water level inside the containers. When this part of air was used up, combus- tion stopped. Mayow named the air that supported combustion “nitro-aereus”. His experiments were advanced in his time. For example, at the beginning of the experiment, he used a U-shaped syphon to equalize the pressure inside and outside the container. For the burning candle experiment, the syphon was quickly removed after the container was in place. This procedure made the experiment more accurate.
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Above are Mayow’s apparatuses for studying animal respiration described in his TractatusQuinque Medi- co-Physici published in 1674. He discovered that animal respiration was similar like combustion, both of which consumed a portion of the air. In the left apparatus, the respiration of a mouse caused the blad- der membrane to bulge inside. In the right apparatus, the respiration of a mouse caused the water level to increase inside the container. When the part of air that support respiration was used up, animals died. Mayow thought that respiration and combustion were similar as both processes consumed the “ni- tro-aereus” (i.e. oxygen). Mayow argued that during respiration the nitro-aereus reacted with substances inside blood, providing body heat for the animals. This was an advanced view of respiration during that time.
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Stephen Hales 1677—1761
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Stephen Hales 1677—1761
Stephen Hales was born on September 17th, 1667 in Kent, England. His research mainly focused on plant and animal physiology, and is regarded as the founder of plant physiology. During his research on plants, Hales noticed that the effects of gases on plants, which inspired him to conduct many research on gases and in- vented many apparatuses for preparing and collecting them. Hales believed that all gases are the same element. As a result, he only measured the volume of gases generated in his experiments, paying no attention to their chemical properties. His experiments, however, influenced many scientists, including Cavendish and Priest- ley. On January 4th, 1761, Hales died in Teddington, England (aged 83). His main scientific contributions are:
l In plant physiology, discovery of liquid circulation in plants, explanation of the effects of transpiration (the loss of water from leaves of plants) through well-designed experiments. l In animal physiology, first accurately measuring of blood pressure, discovery of the difference in blood circulation among different animal species. l In pneumatic chemistry, finding that many materials releases gases during heating or fermentation, inventing instruments for generating and collecting gases. l Inventing ventilators for improving air quality in closed environments such as mines, prisons, and ship cabins.
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Above is Hales’ apparatus for generating and collecting gas through heating described in his Vegetable Statick published in 1727. The container for receiving gas had an opening at the bottom. At the begin- ning of the experiment, the water level inside the receiving container was marked. During the experi- ment, generated gas pushed down the water level inside the container, and the volume of the generated gas was determined. Hales was a supporter of four-element theory. He believed that “air” existed in many substances. Through heating these substances, air could be released. He was only interesting in determining the amount of the air. As a result, he missed the opportunity to discover many new gases, possibly including oxygen. However, Hales’s experiments influenced many scientists including Priestley.
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The left is hales’ apparatuses for generating gases through fermentation described in his Vegetable Statick published in 1727. The apparatus on and collecting the left could determine the amount of gas released during fermentation through the change of water level inside the inversed container. The right bottle contained green beans and a small amount of mercury at the bottom. A vertical tube inserted into the mercury through the cork. During fermentation, the pressure built up inside the bottle and raised the mercury inside the tube. By reading the mercury height inside the tube, the pressure could be determined. Similar as the experiments described in the previous page, Hales only cared about the amount of “air” released and not its chemical properties.
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Henry Cavendish 1731—1810
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Henry Cavendish 1731—1810
Henry Cavendish was born on October 10th, 1731 in Nice, Kingdom of Sardinia. Although he was bone in a wealthy family, he was seldom engaged in any social ac- tivities and devoted himself entirely to scientific research. Cavendish’s research was very broad and productive. However because he never published results which he was not completely satisfied, he only published less than 20 research papers in his lifetime. In his unpublished manuscripts, many results were very advanced during his time. Cavendish was famous for his accuracy in his experiments. The density of Earth which Cavendish published in a 1789 paper is different from current value by only 1%. Cavendish died on February 24th, 1810 (aged 78) in London, England. His main scientific contributions are:
l In Chemistry, comprehensively investigating the properties of hydrogen gas, collecting water-soluble gases with mercury for the first time, accurately de- termining the ratio of hydrogen and oxygen in water, accurately determining the composition of the air. l In electrical science,demonstrating that electric force was inversely propor- tional to the distance between two charges, distinguishing the quantity of electric charge and electric potential. l In thermal science,using the theory of latent heat to accurately determining the melting point of mercury, sulfuric acid, nitric acid and other liquids. l In Earth physics, determining the density of Earth through rigorous experi- ment.
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Above are Cavendish’s apparatuses for hydrogen gas preparation and weight measurement described in his paper On Factitious Airs published in 1766. Cavendish found that when metals such as zinc and iron were mixed with hydrochloric acid or dilute sulfuric acid, a flammable gas was released. He called this gas “inflammable air”. At that time, Cavendish was a believer of phlogiston theory. Since when the same amount of a certain metal reacted with different acids resulting in the same amount of inflammable air, he argued that this air came from the metal and was the phlogiston of the metal. We now know that this is not true since inflammable air, i.e. hydrogen gas, comes from hydrogen ions of the acid. In addition, Cavendish determined the relatively accurate density of hydrogen used the apparatus on the right. In- side the tube were powders of potassium carbonate which adsorbed the moisture mixed in the hydrogen gas. Through measuring the change of weight before and after the reaction, the weight and density of hydrogen could be determined.
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Above is Cavendish’s apparatus for transferring and mixing gases described in his paper On Factitious Airs published in 1766. Cavendish knew that mixture of hydrogen and air exploded upon ignition. With this apparatus, he prepared hydrogen-air mixture with different proportion. He discovered the stron- gest exploration occurred when the hydrogen-air ratio was 3:7, corresponding to hydrogen-oxygen ratio of 2.04:1. This value is very close to the 2:1 ratio of hydrogen and oxygen in water. At the time of the experiment, Cavendish did not know the existence of oxygen. Later after the discovery of oxygen, Cav- endish used an improved apparatus to study the explosion of hydrogen-oxygen mixture and determined the hydrogen-oxygen ratio inside water was 2.02:1.
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Carl Wilhelm Scheele 1742—1786
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Carl Wilhelm Scheele 1742—1786
Scheele was born on December 9th, 1742 in Swedish Pomerania (today in Germa- ny). At age of 14, he became an apprentice pharmacist, and got interested in chem- istry. In very basic laboratory, Scheele’s outstanding experimental skills enabled him to make many contributions to chemistry, among which the most famous one was the independent discovery of oxygen around 1773. Scheele lived in poverty for most his life. In 1782 he was finally able to set up his own lab, but soon he suffered from poor health and left the world on May 26th, 1786 (aged 43) in Köping, Swe- den. His main scientific contributions are:
l Discovering oxygen (which Scheele named “fire air”), pointing out that the air is composed of fire air and “foul air” (nitrogen). l Discovering many inorganic substances such as chlorine gas (not knowing it was an element), hydrogen fluoride, and silicon tetrafluoride. l Distinguishing graphite and molybdenum disulfide. l Discovering silver salts decomposed under light exposure, which was the ba- sic principle of early photography. l Discovering many organic acids such as tartaric acid and lactic acid.
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Above is Scheele’s instruments for preparing oxygen described in his Chemische Abhandlung von der Luft und demFeuer published in 1777. Inside the retort was a mixture of potassium nitrate and concentrated sulfuric acid. Upon heating the mixture, a colorless gas was released and collected in the bladder tied to the opening of the retort. Scheele observed that combustion became more intense inside this gas, emit- ting bright light. He named this gas “fire air”, which is the oxygen we know today. He thought that the air around us was composed of fire air which could support combustion and “foul air” (nitrogen) which could not support combustion. Scheele discovered oxygen around 1773. This discovery was published in his book Chemische Abhandlung von der Luft und demFeuer in 1777, which was later than Priestley’s book. However, it is accepted that two scientists both independently discovered oxygen and should share the honor.
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