My Science School

 

          Joseph Priestley discovered a gas in the late 1770s. Sir Humphrey Davy became the first human to inhale it and described it “very pleasurable” and called it ‘laughing gas.’ This gas was nitrous oxide. Priestley’s discoveries were published in 1772 in the book Experiments and Observations on Different Kinds of Air.

          Though Davy discovered that inhaling nitrous oxide could relieve a conscious person from pain, its primary use still remained recreational. These nitrous oxide capers occurred in travelling medicine shows and carnivals where the public paid a small price to inhale a minute’s worth of gas. People would laugh and act silly until the effect of the drug ended abruptly, leaving them confused.

          It wasn’t until another 44 years had gone by, that doctors began to use it for anaesthesia. In the early 1840s, nitrous oxide was used as an anaesthetic in clinical dentistry and medicine.

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          Oxygen is crucial for the survival of humans, animals and plants alike. The complex history of the discovery of oxygen began with it first being discovered by the Swedish chemist Carl Wilhelm Scheele in 1772. He had produced oxygen gas by heating mercuric oxide and various nitrates. As it was the only known agent to support combustion at that time, Scheele called it ‘fire air.’ His manuscript titled Treatise on Air and Fire which he sent to the publisher in 1775 contained an account of his discovery. It was published in 1777.

          Meanwhile, Joseph Priestley had independently discovered oxygen as well as published his findings in 1775. As this paper, titled An Account of Further Discoveries in Air preceded Scheele’s publication by two years; Priestley is given priority in the discovery.

          Another person who also discovered oxygen around this time was Antoine Lavoisier. He was the French chemist who recognized it as an element and even coined the name ‘oxygen.’ The name is derived from the Greek word that means ‘acid former’, a property that oxygen does not really possess.

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          In the November of 1776, the Italian physicist Alessandro Volta scientifically identified methane for the first time. Inspired by a paper written by Benjamin Franklin on ‘flammable air,’ Volta collected the gas rising from the marshes of Lake Maggiore that straddles Italy and Switzerland. He succeeded in isolating methane by 1778.

          The name ‘methane,’ derived from the word ‘methanol’ was coined years later by the German chemist August Wilhelm von Hofmann in 1866. With the chemical formula, methane is the simplest hydrocarbon containing a single carbon atom and four hydrogen atoms. It is a greenhouse gas available in small quantities in the earth’s atmosphere. A principal component of natural gas, methane is flammable and used as fuel all over the world.

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          Though uranium has been in use since ancient times to produce yellow coloured ceramic glazes, Martin Heinrich Klaproth formally discovered uranium in 1789. Klaproth’s discovery came through his study of the mineral pitchblende, which was thought to be an iron or zinc ore. In his experiment, pitchblende was dissolved in nitric acid. Adding potash to this created a yellow precipitate. When more potash was added, this yellow precipitate dissolved. Since these reactions were unlike any Mart known element, Klaproth concluded that he had discovered a new element. As the planet Uranus had recently been discovered, he named the element after it.

          The first sample of uranium metal isolated by heating uranium tetrachloride with potassium was made in 1841 by Eugene-Melchior Peligot in Paris.

          In addition to its value to chemists, uranium was only used as a glass and ceramic colouring agent during the 1800s. This changed when Henri Becquerel discovered radioactivity using uranium in 1896. All isotopes of uranium possess radioactive properties in varying degrees. Uranium came to be used as a fuel in nuclear power plants.

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          The structure of benzene that we know today was deduced from a dream! Benzene is a colourless liquid and its structure has fascinated scientists since its discovery.

          Benzene was first discovered by the English scientist Michael Faraday in 1825. Archibald Scott Couper in 1858 and Joseph Loschmidt in 1861 suggested possible structures that contained multiple double bonds or multiple rings; however the chemists found it difficult to make conclusions without sufficient proof.

          A widely accepted suggestion regarding the structure of benzene was made in 1865 by the German chemist Friedrich August Kekule. He published a paper in French proposing that benzene is made up of a ring of six carbon atoms with alternating single and double bonds. It was said that this solution came to Kekule in a dream in the form of a snake that was eating its own tail. The cyclic nature of benzene was confirmed in 1929 by crystallographer Kathleen Lonsdale.

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          Water is the only compound that exists in solid, liquid and gaseous states on our planet. With its many unique properties, water is vital for our survival.

          Earlier, water was believed to be an element. Its real composition was discovered by the chemist Henry Cavendish. He created an explosion by mixing hydrogen and oxygen called the oxyhydrogen effect and established that water is not an element, but a compound. Cavendish announced the composition of water to the Royal Society, London on January 15th, 1784.

          The decomposition of water by electrolysis into hydrogen and oxygen was first done by English chemists William Nicholson and Anthony Carlisle in 1800. Five years later, Joseph Louis Gay-Lussac and Alexander von Humboldt showed that water is composed of two parts hydrogen and one part oxygen. The formula for water was made in 1811 by the Italian physician Amadeo Avogadro.

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          Avogadro’s law is a fundamental law of gases proposed in 1811.

          It states that equal volumes of different gases contain equal number of molecules under the same temperature and pressure. For example, one litre of Nitrogen gas and one litre of Chlorine gas contain the same number of molecules at Standard Temperature and Pressure (STP). STP is the standard condition often used for measuring gas density and volume, where air is at 0 degree Celsius.

         In the 1800s, scientists were still learning the difference between atoms and molecules. Therefore, discovering that the volume of a gas was directly proportional to the number of particles it contained, was revolutionary. It was crucial in establishing the formulas for simple molecules. Over time, it was understood that gases show small deviations from the ideal behaviour and the law holds only approximately.

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          Some ions or molecules have identical formulas but different structures; these are called isomers. Because they have identical formulas, each isomer contains the same number of atoms though their atomic arrangement would be different. Let’s take a look at glucose and fructose. Both glucose and fructose have the same chemical formula but they have two distinct structures.

          Friedrich Wohler was the first to notice this phenomenon. In 1827, Wohler realised while preparing silver cyanate that despite having the same elemental composition as silver fulminate, its properties were entirely different. Wohler’s discovery challenged the prevailing chemical understanding.

          Isomerism was accepted widely after similar discoveries were made. For example, Wohler himself discovered another pair of compounds-urea and ammonium cyanate in 1828. They too had same atomic compositions but were chemically distinct. Jons Jacob Berzelius introduced the term isomerism to describe this phenomenon.

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          Urea or carbide was first discovered in human urine by H.M. Rouelle in the year 1773. Friedrich Wohler synthesised it in 1828 during an attempt to make ammonium cyanate, as a part of his ongoing study of cyanates. On treating silver cyanate with ammonium chloride solution, he obtained a white crystalline material which proved identical to urea obtained from urine.

          Urea became the first organic compound to be synthesised from inorganic starting materials. Wohler’s synthesis also marked the beginning of organic chemistry, the first in-vitro synthesis of a chemical compound otherwise produced only by living systems.

          Urea is a normal component of blood and many tissues.

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          When a chemical reaction is started with electricity, it is called electrolysis. It is usual for reactions involving liquids, especially with ions dissolved in water.

          You know what ions are. Ions are atoms or molecules containing unequal number of protons and electrons, making it charged. Electrolysis was first performed in 1785 when Martinus van Marums used an electrostatic generator to reduce tin, zinc, and antimony from their salts.

          William Nicholson and Anthony Carlisle found the composition of water using electrolysis. Electrochemistry began with the electrolysis of water and helped scientists learn more about the nature of chemical compounds.

          The word “electrolysis” was introduced by Michael Faraday in the 19th century. The process is commercially relevant as an electrolytic cell is used at a stage in the separation of elements from naturally occurring sources such as ores.

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          The modern periodic table lists the elements in the order of increasing atomic number, which is the number of protons in the nucleus of an atom.

          One of the initial attempts to classify the elements was done by Antoine Lavoisier in 1789. He classified them as gases, non-metals, metals and earths based on their properties. In 1829, triads of elements with chemically similar properties such as sodium, lithium and potassium were recognized by Johann Dobereiner. In the following decades many attempts were made to group elements together.

          A pivotal classification at came in 1866 when Russian chemist Dmitry Mendeleev listed the elements by atomic weight. He identified a pattern wherein similar elements appeared at regular intervals or periods. Mendeleev first published his periodic table in 1869 followed by a revised version in 1871. It left gaps where a break in the pattern occurred. He correctly predicted that those gaps represented undiscovered elements.

          Julius Lothar Meyer was a contemporary of Mendeleev. Meyer also produced several periodic tables between 1864 and 1870. His 1868 table listed the elements in order of atomic weight, with elements with the same valency arranged in vertical lines, remarkably like Mendeleev’s table. Unfortunately, Meyer’s work was not published until 1870 after Mendeleev’s table had been published.

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          An electron is a negatively charged subatomic particle represented by the symbol e-. The mass of an electron is only 1/1836 that of a proton.

          Electrons were discovered by J. J. Thomson in 1897. He was studying the properties of cathode rays. Thomson constructed a glass tube from which much of the air was pumped out and then he applied a high electrical voltage between two electrodes at either end of the tube.

          He detected that a stream of particles (ray) was coming out from the negatively charged electrode (cathode) to the positively charged electrode (anode). This ray was called cathode ray. He proved that these cathode rays could be deflected, or bent, which meant that they were made of small particles. He named these particles ‘corpuscles.’ Thomson initially underestimated the relevance of his discovery. He had assumed that it was too insignificant to be of importance to those outside a lab. However, the magnitude of this discovery was soon realised. The name ‘electron,’ advocated by G. F. Fitzgerald, J. Larmor, and H. A. Lorenz was adopted by the scientific community.

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          In 1896, Henri Becquerel was using naturally fluorescent minerals to study the properties of X-rays. He exposed potassium uranyl sulfate to sunlight and then placed it on photographic plates wrapped in black paper. He believed that uranium absorbed the Sun’s energy and then emitted it as X-rays.

          This assumption was later proved wrong. Because it was cloudy and overcast in Paris when Becquerel did his experiment, he expected it to fail because uranium needed sunlight as per his belief. However, when he developed the photographic plates anyway, Becquerel found strong and clear images! This proved that uranium emits radiation without an external energy source and thus radioactivity was discovered.

          The term radioactivity was coined by Marie Curie, who together with her husband Pierre began investigating the phenomenon discovered by Becquerel. They extracted uranium from an ore and were surprised to find the leftover ore more radioactive than pure uranium. Their conclusion that the ore had more radioactive elements led to the discovery of polonium and radium.

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          Alizarin is an organic compound that has been in use as red dye, particularly for textiles. It’s traditionally derived from the roots of plants of the madder genus.

          German chemists, Carl Graebe and Carl Lieberman working for the chemical company BASF found a way to synthesise alizarin in 1868. They demonstrated that the compound could be made from a chemical called anthracene, extracted from coal tar. This mode of production was cheaper as well. Simultaneously, the English dye chemist William Henry Perkin had independently discovered the same synthesis. However, the BASF group filed their patent one day before Perkin.

          As one of the few red dyes available at that time, production of natural alizarin provided livelihood to thousands of people until it began to be synthetically produced. Synthetic alizarin was produced commercially at a fraction of the cost of the natural dye. The use of alizarin has decreased over the years.

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          Saccharin is used as a sugar-substitute in food and drinks regardless of its unpleasant aftertaste. This is mainly because it is sweeter than sugar and does not make people fat. Saccharin was first produced accidentally in 1879 by Ira Remsen and Constantin Fahlberg, two chemists working on coal tar derivatives in Ira Remsen’s laboratory.

          Constantin Fahlberg found an unaccountable sweet taste to his food despite thoroughly washing his hands after leaving the lab. He inspected the laboratory apparatus by taste test and finally discovered the source, which turned out to be saccharin. Fahlberg and Remsen published their findings in 1880.

          Saccharin is the first commercially available artificial sweetener. Describing the method of production, Fahlberg applied for patents in different countries in 1884. Subsequently, he began producing it commercially within two years and amassed considerable wealth. This created some conflict as Ira Remsen was excluded from the patent which claimed Constantin Fahlberg to be solely responsible for the discovery.

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