Marie and Pierre Curie proved the existence of the new element radium when they chemically isolated one-tenth of a gram of pure radium chloride.

Marie and Pierre Curie were both pioneering scientists in their own right, but as a research partnership they are most famous for their work on radioactivity. Inspired by the work of the French physicist Henri Becquerel who had been the first person to discover radioactivity, the Curies’ work won them the 1903 Nobel Prize in Physics which they shared with Becquerel himself.

Marie had been born and raised in Poland but, since women were not permitted to attend university there, she moved to France to take up a place to study at the Sorbonne in Paris. Having secured degrees in both physical sciences and mathematics by 1894 she married Pierre, an established physicist, whom she had met through a mutual friend. Marie subsequently began to pursue a Ph.D. for which she studied the recently-discovered rays emitted by uranium.

Having coined the term radioactivity to describe the radiation she observed, Curie focused on the minerals pitchblende and torbernite in her search for materials that emitted more radiation than uranium itself. Inspired by his wife’s discovery that the element thorium was radioactive, Pierre dropped his own research in 1898 to work with her. In July they published a joint paper announcing the existence of an element they named polonium, and in December they did the same for radium.

To unequivocally prove their existence, the Curies sought to isolate them from pitchblende. Having processed tons of the mineral, they eventually obtained one-tenth of a gram of radium chloride on 20 April 1902, for which they shared the 1903 Nobel Prize in Physics.

The DuPont company’s organic chemist Wallace Carothers received a patent for linear condensation polymers, the basis of the material better known as nylon.

Carothers joined DuPont from Harvard University, where he had taught organic chemistry. He was initially reluctant to move due to concerns that his history of depression would be a problem in an industrial setting, but DuPont executive Hamilton Bradshaw persuaded him otherwise and he took up his role in February 1928.

Having thrown himself into researching the structure and synthesis of polymers, Carothers and his team were responsible for creating the first synthetic replacement for rubber which was later named neoprene. Their laboratory, which was nicknamed “Purity Hall”, then began to focus on producing synthetic fibres that could be used in place of silk as this was becoming harder to source due to declining relations with Japan following the Great Depression.

On 28 February 1935 Carothers produced a fibre initially referred to as polyamide 6-6 as its components had six carbon atoms. Although the manufacturing process was complicated, DuPont were excited by the new material’s strength and elasticity and ordered the laboratory to press ahead with their research. However, plagued by depression, Carothers committed suicide in a hotel room in April 1937 by drinking potassium cyanide dissolved in lemon juice.

DuPont continued to refine the manufacturing process and revealed women’s stockings made of nylon, as it became known, at the 1939 New York World’s Fair. By the time the first pairs were made commercially available in 1940, the company had invested $27 million into the development of a material that is now found in everything from guitar strings to medical implants.

On the 6th March 1869, Russian chemist Dmitri Mendeleev presented his periodic table to the Russian Chemical Society. While not the first to attempt to classify the elements, Mendeleev’s system was the one to gain universal acceptance.

Mendeleev was both a teacher and an academic chemist, and in the early 1860s published a prize-winning textbook that placed him at the forefront of chemical education. He was, however, frustrated by the apparent disorder of the chemical elements so set about developing a way to classify them.

Other scientists had tried to find ways to arrange the elements since the 18th Century. Just a few years before Mendeleev’s periodic table, the English chemist John Newlands published his ‘Law of Octaves’ which classified the known elements into eight groups in order of their relative atomic masses. However, Newlands’ work was ridiculed at the time and was only formally recognised in 1887.

Mendeleev, meanwhile, continued his work to classify the elements. Tradition dictates that he wrote the characteristics of the known elements on cards, and played a game of ‘chemical solitaire’ with them. He apparently fell asleep during one of these card games, and had a dream in which he saw the cards “fall into place”. Mendeleev realised that the features of the elements repeated in a predictable pattern, based on their atomic weight. While this led to there being some gaps or spaces in ‘periods’ where he believed an element should exist, he was able to calculate the missing element’s atomic mass and properties. His predications later turned out to be correct when missing elements such as gallium were discovered.