A natural philosopher, the greatest experimental and theoretical English chemist and physicist of his age, Henry Cavendish (10 Oct. 1731 – 24 Feb. 1810) was distinguished for great accuracy and precision in researches into the composition of atmospheric air, the properties of different gases, the synthesis of water, the law governing electrical attraction and repulsion, and calculations of the density (and hence the weight) of the Earth.
Cavendish attended Cambridge University from 1749 to 1753, but left without a degree. He engrossed himself in scientific studies but did not bother to publish a number of his important discoveries as Cavendish was sociable only with his scientific friends. Even the only existing portrait of him was sketched secretly. He approached most of his investigations through quantitative measurements.
Contributions and Achievements:
He was the first to recognize hydrogen gas as a distinct substance for which he calculated its density as well as the densities of several other gases. He showed that hydrogen produced dew, which appeared to be water, upon being burned. He also found hydrogen to be much less dense than air. Cavendish also investigated the products of fermentation, showing that the gas from the fermentation of sugar is indistinguishable from the “fixed air” characterized as a constituent of chalk and magnesia by Black (in modern language, carbon dioxide). In his study of the methods of gas analysis Cavendish made one amazing observation.
He was glinting air with excess oxygen (to form oxides of nitrogen) over alkali until no more absorption took place and noted that a tiny amount of gas could not be further reduced, “so that if there is any part of the phlogisticated air of our atmosphere which differs from the rest, and cannot be reduced to nitrous acid, we may safely conclude that it is not more than 1/120 part of the whole.” As is now known, he had observed the noble gases of the atmosphere.
In addition to his achievements in chemistry, Cavendish is also known for the Cavendish experiment, the first to measure the force of gravity between masses in a laboratory and to produce an accurate value for Earth’s density. The apparatus he was working with was devised by the Rev. John Michell, though he had the most important parts reconstructed to his own designs, it depended on measuring the attraction exercised on a horizontal bar, suspended by a vertical wire and bearing a small lead ball at each end, by two large masses of lead. His work and constant observation led others to accurate values for the gravitational constant (G) and Earth’s mass.
Based on his results, one can calculate a value for G of 6.754 × 10-11N·m2/kg2, which compares favorably with the modern value of 6.67428 × 10-11N·m2/kg2.
Cavendish compared the electrical conductivities of equivalent solutions of electrolytes and expressed a version of Ohm’s law. He was not the first to profound an inverse-square law of electrostatic attraction, but Cavendish’s exhibition, based in part on mathematical reasoning, was the most effective. He founded the study of the properties of dielectrics and also distinguished clearly between quantity of electricity and what is now called potential.
Cavendish’s work and reputation have to be considered in two parts, the one relating to his published work, the other to the large amount he did not publish. During his lifetime he made notable discoveries in chemistry and physics mainly for which he is known the best and recognized.