Henry Cavendish was an English natural philosopher and a theoretical and experimental chemist and physicist. He is mostly known for discovering hydrogen, which is today known as “inflammable air”. Personally, Cavendish was a shy man with great accuracy and precision highlighted in his experiments related to atmospheric air composition, properties of different gases, a mechanical theory of heat and the synthesis of water, etc.
He also measured the density of the earth referred to as the Cavendish experiment. Let’s take a look into how Henry Cavendish became one of the most important personalities of his time.
What history tells us about Henry Cavendish is that he was born in Nice in 1731. He lived with his family at the time and his mother Lady Anne de Grey was the fourth daughter of Henry Grey, 1st Duke of Kent, while his father was Lord Charles Cavendish was the third son of William Cavendish, 2nd Duke of Devonshire. The family traced its roots to Norman times and was known to have close connections with many aristocratic families of Great Britain.
Unfortunately, Henry’s mother died after the birth of her second son and shortly before Henry’s second birthday. Henry Cavendish was styled as “The Honorable Henry Cavendish”. As he turned 11, Henry attended a private school in London called Newcome’s School. Upon turning 18 he entered the University of Cambridge in St.Peter’s College.
However, three years later, he left without taking a degree. He then moved in with his father and soon formed his own laboratory. Lord Charles Cavendish early life pretty much included participation in politics but later saw his interest growing in science. In 1758, he took Henry to attend the meetings of the Royal Society as well as the dinners.
Two years later, Henry was elected to both groups but hardly attended. He was not virtually interested in politics and followed his father in science, researchers, and participation in scientific organizations.
Eventually, his expertise and interest in the utilization of scientific experiments led him to head a committee to review the Royal Society’s meteorological instruments and help assess the instruments of the Royal Greenwich Observatory.
While Henry’s father was near death, he began working with Charles Blagden, an association that allowed Blagden to fully enter London’s scientific society. At the time, Blagden did much to keep the world away from Cavendish.
Meanwhile, Cavendish did not do much but published a few papers. His several researches on optics, mechanics, and magnetism featured exclusively in his manuscripts but rarely made it in his published work.
Henry found out that a peculiar, definite, and highly inflammable gas, which is known as “Inflammable Air” was produced as a result of certain reactions of acids on certain metals. This gas was hydrogen, rightly pointed out by Cavendish.
Although hydrogen was already discovered and prepared by Robert Boyle but Cavendish is credited for recognizing its elemental nature. The year 1777 saw, Cavendish, announcing that the air exhaled by mammals is converted to “fixed air” not “phlogisticated air” as predicted by Joseph Priestly.
In addition to that, Cavendish also produced Carbon dioxide by dissolving alkalis in acids along with other gases in bottles inverted over water or mercury. Furthermore, he then measured their specific gravity, solubility in water and also noted their combustibility.
He then concluded in his paper published in 1778 titled “General Considerations on Acids” that respirable air constitutes acidity. In return, the Royal Society awarded Cavendish the Copley Medal for this paper.
Then, the year 1783 saw Cavendish publishing a paper on eudiometry. He then continued to describe a new eudiometer of his invention, which allowed him to achieve the best results. Then, in 1781 Cavendish by repeating an experiment published a paper in which he described the production of pure water by burning hydrogen in “dephlogisticated air”. He noted that the burning of hydrogen instead of being synthesized caused water to condense from the air.
In 1785, Cavendish investigated the composition of common air and managed to obtain precisely accurate results. He combined both hydrogen and ordinary air in known ratios, which then caused an explosion with a spark of electricity.
Eventually, after performing several experiments, Cavendish through careful measurements concluded that common air consists of one part of dephlogisticated air mixed with four parts of phlogisticated nitrogen.
In the 1890s, Lord Rayleigh and William Ramsay realized that their newly discovered inert gas, argon was the reason behind Cavendish’s problematic residue. Therefore, he had not made an error. Over time, Cavendish worked closely with his instrument makers and improved his existing instruments rather than making new ones.
The density of the Earth
Soon after the death of his father, Henry bought another house in Clapham Common. While the London house contained a bulk of his library, the Clapham Common consisted of most of his instruments. This was also the place where he conducted most of his experiments.
Amongst the experiments conducted, the most notable was the one that measured the density of the Earth and became known as the Cavendish experiment. The instrument used by Cavendish was the modification of the torsion balance built by Englishman and geologist John Michell.
The instrument was sent in crates, while Cavendish completed the experiment in 1797-1798 and published the results. The apparatus used by Cavendish featured a torsion balance of 2-inch pair 1.61-pound lead spheres suspending from the arm of a torsion balance and two much larger stationary lead balls. Cavendish planned to measure the gravitational force or attraction between the two.
At the same time, he realized that Michell’s apparatus would be too sensitive to the temperature differences and induced air currents. Therefore, he made some modifications by isolating the apparatus in a separate room using external controls and telescopes for making observations.
Cavendish found out that the average density of the earth is 5.48 times greater than that of water. John Henry Poynting pointed out that the value should have been 5.448. But what was surprising about Cavendish’s experiment was that he was able to eliminate every source of error and factor that might disturb the experiment.
Chemist Henry Cavendish also conducted several electrical and chemical experiments. Similar to the theory of heat, his comprehensive theory of electricity was in mathematical form and was based on precise quantitative experiments.
While working with his colleague Timothy Lane, he was able to create a torpedo that could dispense electric shocks. Cavendish wrote many electrical topics for the Royal Society but the bulk of his experiments were not known until James Clerk Maxwell collected and published them. This was atleast a century after Cavendish’s initial finding and long after other scientists had been credited with the same results.
Cavendish died in 1810 as one of the wealthiest men in Britain. He was recalled as the most knowledgeable of the rich by Jean Baptiste Biot. Cavendish was a shy individual who seldom attended the meetings of the Royal Society and focused on experiments.
However, he was still much respected by his contemporaries. Since he was mostly secretive about his behavior, he avoided publishing most of his work. As the world found out about his achievements, Cavendish became known as one of the most important personalities of the 18th century.