He first isolated chlorine, and determined the individuality of manganese and baryta. He was an independent discoverer of oxygen, ammonia, and hydrogen chloride. He discovered also hydrofluoric, nitro-sulphonic, molybdic, tungstic, and arsenic, among the inorganic acids; and lactic, gallic, pyrogallic, oxalic, citric, tartaric, malic, mucic, and uric acids among the organic acids. He isolated glycerine and milk-sugar; determined the nature of microcosmic salt, borax, and Prussian blue, and prepared hydrocyanic acid. He demonstrated that graphite is a form of carbon. He discovered the chemical nature of sulphuretted hydrogen, arsenuretted hydrogen, and the green arsenical pigment known by his name. He invented new processes for preparing ether, powder of algaroth, phosphorus, calomel, and magnesia alba. He first prepared ferrous ammonium sulphate, showed how iron may be analytically separated from manganese; and described the method of breaking up mineral silicates by fusion with alkaline carbonates. Scheele’s contributions to chemical theory were slight and unimportant, but as a discoverer he stands pre-eminent.
Of the French phlogistians we have space only to mention Duhamel and Macquer.
Henry Louis Duhamel du Monceau was born at Paris in 1700. He was one of the earliest to make experiments on ossification, and one of the first to detect the difference between potash and soda.
Peter Joseph Macquer was born in 1718 at Paris. He investigated the nature of Prussian blue (discovered by Diesbach, of Berlin, in 1710), worked on platinum, wrote one of the best text-books of his time, published a dictionary of chemistry, and was an authority of the chemistry of dyeing.
In addition to those already mentioned, the most notable names as workers in chemistry in Great Britain during the eighteenth century are Black, Priestley, and Cavendish.
Joseph Black was born in 1728 at Bordeaux, where his father was engaged in the wine trade. A student of the University of Glasgow, he became its Professor of Chemistry in 1756. In 1766 he was transferred to the Chemical Chair of the University of Edinburgh, and died in 1799. Black published only three papers, the most important of which is entitled Experiments upon Magnesia Alba, Quicklime, and Other Alkaline Substances. He proved that magnesia is a peculiar earth differing in properties from lime. Lime is a pure earth, while limestone is carbonate of lime. He showed that magnesia will also combine with carbonic acid, and he explained that the difference between the mild and caustic alkalis is that the former contain carbonic acid, whereas the latter do not. He also explained how lime is able to convert the mild alkalis into caustic alkalis. Simple and well known as these facts are to-day, their discovery in 1755 excited great interest, and marked an epoch in the history of chemistry. Black’s name is associated with the discovery of latent and specific heat, and he made the first determinations of the amount of heat required to convert ice into water.
Joseph Priestley.
From a mezzotint after Fuseli in the possession of the Royal Society.
Joseph Priestley, the son of a clothdresser, was born in 1733 at Fieldhead, near Leeds. When seven years of age, on the death of his mother, he was taken charge of by his aunt, and was educated for the Nonconformist ministry, eventually becoming a Unitarian. He was first attracted to science by the study of electricity, of which he compiled a history. At Leeds, where he had charge of the Mill Hill congregation, he turned his attention to chemistry, mainly from the circumstance that he lived near a brewery and had the opportunity of procuring large quantities of carbonic acid, the properties of which he carefully studied. He abandoned the ministry for a time to become librarian and literary companion to Lord Shelburne, with whom he remained seven years. During this time he industriously pursued chemical inquiry, and discovered a large number of æriform bodies—viz., nitric oxide, hydrogen chloride, sulphur dioxide, silicon fluoride, ammonia, nitrous oxide, and, most important of all from the point of view of chemical theory, oxygen gas. Priestley’s work gave a remarkable impetus to the study of pneumatic chemistry. It exercised great influence on the extension of chemical science, and—in other hands than his—on the development of chemical theory. The most important of his contributions to science are contained in his Experiments and Observations on Different Kinds of Air. This work not only gives an account of the methods by which he isolated the gases he discovered, but describes a great number of incidental observations, such as the action of vegetation on respired air, showing that the green parts of plants are able in sunlight to decompose carbonic acid and to restore oxygen to the atmosphere. He was, in fact, one of the earliest to trace the specific action of animals and plants on atmospheric air, and to show how these specific actions maintained its purity and constancy of composition. He initiated the art of eudiometry (gas analysis), and was the first to establish that the air is not a simple substance, as imagined by the ancients. Priestley is to be credited with the invention of soda-water, which he prepared as a remedy for scurvy; and his name is connected with the so-called pneumatic trough—a simple enough piece of apparatus, but one which proved to be of the greatest service to him in his inquiries.
After leaving Lord Shelburne, Priestley removed to Birmingham and resumed his ministry. His religious and political opinions made him obnoxious to the Church and State party; and during the riots of 1791 his house was wrecked, his books and apparatus destroyed, and his life endangered. Eventually he emigrated to America, and settled at Northumberland, where he died on February 6th, 1804, in the seventy-first year of his age.