Joseph Black treated limestone with acid and collected the gas evolved in a Hales pneumatic trough. He weighed the gas and the remainder of the limestone, finding that what the limestone lost was equivalent to the weight of the gas. He then reversed the process and succeeded in making chalk from a solution of lime. This simple experiment paved the way for chemical analysis and syntheses which have added profoundly to our knowledge of the composition of matter.
Bergman tested Black's gas with litmus and found it gave an acid reaction and in 1779 Lavoisier demonstrated that it consisted of carbon and oxygen.
Priestley and Cavendish, both English chemists, then took up this study. Cavendish treated iron, tin, zinc, and other metals with sulphuric acid and discovered a new gas which he termed hydrogen.
Rutherford discovered nitrogen in 1772 and Priestley isolated nitric oxide, and in 1774 discovered oxygen. In the course of his experiment Priestley also discovered ammonia, sulphur dioxide and other chemicals.
His greatest achievements, however, were the isolation and recognition of oxygen, and the discovery of the composition of water. Following up these discoveries, he noted that the air is not a simple elementary substance, but a mixture of nitrogen and oxygen with several impure gases. The work of this great chemist became as fruitful in the chemical field as that of Newton in physics, astronomy, and mathematics.
Carl Wilhelm Scheele, a Swede, carried out many experiments which resulted in the discovery of tartaric acid, the decomposition of silver chloride by light, magnesium nitrate, magnesia, microcosmic salt, and sulphureted hydrogen, chlorine, hydrofluoric, and other inorganic acids. He also discovered the following organic acids: lactic, gallic, pyrogallic, oxalic, citric, malic, mucic and uric. He isolated glycerin and sugar of milk and determined the nature of hydrocyanic acid, borax, plumbago, Prussian blue, and other chemicals. He invented many new chemical and laboratory processes. Scheele was an apothecary's assistant and lived in poverty. But although his experiments were conducted under disadvantageous circumstances his discoveries ranked him as the greatest chemist of his time and one of the greatest chemical experimenters of all time.
Cavendish established the proportions of the constituents of air, demonstrated the nature of water and its volumetric composition. The character of the experiments conducted by Cavendish, his elegant methods of weighing, measuring and calculating have caused him to be looked upon as the founder of systematic chemistry. He was more scientific in his methods than the brilliant Lavoisier, and much more learned and philosophical than the practical Scheele.
While the chemists were making these great advances there were important developments in physical science. Benjamin Franklin (1706-1790), the first American scientist to acquire world-wide fame, announced that lightning was an electrical phenomenon. In 1752 he showed by his famous kite experiments that atmospheric and machine-generated electric charges are of a like nature.
Franklin suggested to Cavendish certain electrical experiments with a view to studying the electric force between two charges. These experiments led Cavendish to the discovery of the law of electric attraction between charged bodies. Franklin subsequently discovered the law of conservation of an electric charge.