THE DISCOVERY OF GASES - Cavendish 3#

Cavendish

Henry Cavendish was an English physicist and chemist. He was born in Nice at 1731.

Figure 17. Henry Cavendish (1731 – 1810)

His great contributions to science resulted from his many accurate experiments in many fields. His chief researches were on heat, in which he determined the specific heats for a number of substances; on the composition of air; on the nature and properties of a gas that he isolated and described as “inflammable air” and that Lavoisier later named “hydrogen”; and on the composition of water, which he demonstrated to consists of oxygen and his “inflammable air”.

Cavendish’s first publication on chemistry was his paper On Factitious Airs (1766), devided into three parts. In his paper, he described the manipulation of gases, including collection in bottles filled with water, etc. In his experiments on inflammable air, Cavendish obtained it by the action of dilute sulphuric acid and hydrochloric acid (spirit of salt) on zinc, iron and tin. He found that “the air is the same and of the same amount whichever acid is used to dissolve the same weight of any particular metal”, and hence concluded that it came from the metal and not from the acid. He calls it “the inflammable air from metals”.

Cavendish was a believer in the theory of phlogiston and would represent the action of an acid on a metal as :

calx + φ + acid = calx + acid + φ

metal salt inflammable air

Cavendish says, “their phlogiston (i.e. that in the metals) flies off, without having its nature changed by the acid and forms the inflammable air”.

The inflammable air differed from fixed air in being insoluble in water and alkali. Cavendish found that it formed an explosive mixture with air, the most violent detonation being with a mixture of three volumes of inflammable air with seven volumes of common air.