Page:Popular Science Monthly Volume 35.djvu/828

802 have raised chemistry to its present important position, together with the insight into the manifold changes and metamorphoses which terrestrial matter has undergone in past times, and which it still undergoes, and into the processes active in vegetable and animal organisms.

The events preceding the discovery of the composition of water afford a striking instance of how many difficulties had to be overcome from the very first observations on the chemical nature of this body—ubiquitous on the surface of the earth—to the ascertainment of its composition, and to our ability voluntarily to prepare it. In the middle ages the doctrine of Aristotle was predominant, that all matter consisted of four elements—air, fire, earth, and water—difference in properties being ascribed only to the varying proportions in which these elements were present. Not much more was known of its physical and chemical characters, but that it may be brought into a solid state by cold and volatilized by heat, and that it offers a good solvent for many substances. Paracelsus, a prominent physician and chemist of the sixteenth century, found that, on treating iron with sulphuric acid, a gas is given off. Boyle, in 1672, discovered this gas to be inflammable; thirty years later, its detonating properties in contact with air became known; but not until Cavendish, in 1766, devoted himself to the exact study of this gas was there any conjecture established on the relations existing between it and water. In 1787 Cavendish made the discovery that, by combustion of this gas in air, water is generated; but, prejudiced by the chemical theories then prevailing, he failed to explain the process in the right way. We are indebted to Lavoisier for a correct definition of the changes taking place in the combustion of hydrogen, which name he gave to the gas in question, signifying a body from which water may be generated by uniting it with oxygen. Thus Lavoisier, supported by the discovery of oxygen by Priestley and Scheele in 1774, became the originator of chemical synthesis. It is a trifling experiment nowadays to demonstrate the formation of water by placing an inverted glass over a jet of burning dry hydrogen, when a dew of water will cover the sides of the vessel and gradually gather into drops.

A rapid advance in synthetical knowledge took place during the third and fourth decades of this century, the artificial preparation of a long series of organic compounds becoming known; and it is a surprising fact, although the chemistry of the carbon compounds, or organic chemistry, was in an infantile state at that time, while most mineral bodies were pretty well known as to their composition and character, that the manufacturing of the former with all their physical and chemical properties was successfully performed, while the imitation of minerals in their