[1] I have borrowed these illustrations of the alchemical, experimental method from M. Hoefer's "Histoire de la Chimie," quoted in the "Encyclopaedia Brittanica," art. "Alchemy." [2] "Ripley reviv'd: or an exposition upon Sir George Ripley's Hermetico-poetical works," by Eirenaeus Philalethes. London, 1678. [3] Browning's "Paracelsus." CHAPTER II. ESTABLISHMENT OF CHEMISTRY AS A SCIENCE--PERIOD OF BLACK, PRIESTLEY AND LAVOISIER. _Joseph Black_, 1728-1799. _Joseph, Priestley_, 1733-1804. _Antoine Laurent Lavoisier_, 1743-1794. During this period of advance, which may be broadly stated as comprising the last half of the eighteenth century, the aim and scope of chemical science were clearly indicated by the labours of Black, Priestley and Lavoisier. The work of these men dealt chiefly with the process of combustion. Black and Priestley finally proved the existence of airs or gases different from common air, and Lavoisier applied these discoveries to give a clear explanation of what happens when a substance burns. * * * * * JOSEPH BLACK was born near Bordeaux in the year 1728. His father was of Scottish family, but a native of Belfast; his mother was the daughter of Mr. Gordon, of Hilhead in Aberdeenshire. We are told by Dr. Robison, in his preface to Black's Lectures, that John Black, the father of Joseph, was a man "of most amiable manners, candid and liberal in his sentiments, and of no common information." At the age of twelve Black was sent home to a school at Belfast; after spending six years there he went to the University of Glasgow in the year 1746. Little is known of his progress at school or at the university, but judging from his father's letters, which his son preserved, he seems to have devoted himself to study. While at Glasgow he was attracted to the pursuit of physical science, and chose medicine as a profession. Becoming a pupil of Dr. Cullen, he was much impressed with the importance of chemical knowledge to the student of medicine. Dr. Cullen appears to have been one of the first to take large and philosophical views of the scope of chemical science, and to attempt to raise chemistry from the rank of a useful art to that of a branch of natural philosophy. Such a man must have been attracted by the young student, whose work was already at once accurate in detail and wide in general scope. In the notes of work kept by Black at this time are displayed those qualities of methodical arrangement, perseverance and thoroughness which are so prominent in his published investigations and lectures. In one place we find, says his biographer, many disjointed facts and records of diverse observations, but the next time he refers to the same subjects we generally have analogous facts noted and some conclusions drawn--we have the beginnings of knowledge. Having once entered on an investigation Black works it out steadily until he gets definite results.