The Romance of Modern Chemistry

CHAPTER XXX i HOW TRIFLING OBSERVATIONS LEAD TO GREAT DISCOVERIES THE scientist who is advancing into the unknown generally sets out with the object of searching for something which his theories lead him to believe is to be found in the unexplored region just ahead. It frequently happens, however, that as he steadily plods forward he discovers something by the way which is of much greater importance than the ultimate object of his search. The story of the ways in which some such un- expected discoveries have been made is interesting, if not romantic, and the rehearsal of one or two of these will show the reader how much depends sometimes on a casual occurrence, and on the observer’s readiness to note what happens and to take advantage of it The discovery of oxygen, the important element which forms one-fifth by volume of the air, was made in a very casual sort of fashion about 140 years ago. Priestley, we are told, was very proud of a burning-glass which had come into his possession, and was going round his laboratory one day concentrating the sun’s rays with this lens, and focussing them on all sorts of substances. Among the materials which he thus happened to expose to the heat of the concentrated solar rays was oxide of mercury, which, as we now know, is very readily split up 225