“THE MAN WHO WEIGHED THE EARTH”

CavendishExperiment

Henry Cavendish was born on 10 October 1731 in Nice, France, where his family was living at the time. His father Lord Charles Cavendish, a Fellow of the Royal Society of London, was the son of the 2nd Duke of Devon shire. His family could trace its lineage across eight centuries to Norman times.

Henry Cavendish was one of those whose works paved the way for proper understanding of chemical elements, their nature, the way they react with one another and the processes taking place in chemical reactions. Cavendish contributed significantly towards better understanding of gases. Cavendish did not publish most of his work. This was perhaps largely due to his peculiar social and secretive behavior. He did not even discuss about his findings with fellow scientists. So, there is no wonder that the vast amount of his unpublished works had things for which others had been given credit. Among these were Richter’s Law of Reciprocal Proportions, Ohm’s Law, Dalton’s Law of Partial Pressures, Coulomb’s Law, and Charles’ Law of Gases.

Most of Cavendish’s electrical studies remained in unpublished. His notebooks and manuscripts containing his electrical studies discovered after almost 100 years were edited by James Clerk Maxwell. Among the major discoveries of Cavendish in the area of electricity are:

  • The concept of electric potential, which Cavendish called the “degree of electrification”.
  • The formula for the capacitance of a plate capacitor.
  • The concept of dielectric constant of a material.
  • The relationship between electric current and electric potential, now called Ohm’s Law.
  • Laws for the division of current in parallel circuits, now attributed to Charles Wheatstone.
  • Inverse square law of variation of electric force with distance, now called Coulomb’s Law.

In 1766, Cavendish isolated and studied hydrogen gas. He produced hydrogen gas by reacting metals with strong acids. It may be noted that even before Cavendish, hydrogen gas was prepared by others, for example, Robert Boyle. However, it is Cavendish who is usually given the credit for recognising the elemental nature of hydrogen. Cavendish’s careful studies involving specific gravities of gases established hydrogen gas as an individual substance. The name “hydrogen”, derived from Greek words meaning “to give rise to.

Cavendish determined the compositions of water and of nitric acid. He found that volume ratio of oxygen and hydrogen in water was 2:1. In 1783, Cavendish determined the composition of Earth’s atmosphere with great accuracy. He concluded that “common air consisted of one part of dephlogisticated air (oxygen)’, mixed with four of phlogisticated (nitrogen)”.

In 1783-84, Cavendish demonstrated that hydrogen reacted with oxygen to produce water. In this way Cavendish demonstrated that water is a combination of two gases and not an element. It was a path-breaking discovery. Since the days of Aristotle water was regarded as one of the four elements of which all substances were made.

 

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