This is really one of the processes supposed to be involved in the transmutation of the metals and might, therefore, perhaps, with propriety, be included under that head. But as it has received special attention in the apocryphal works of Hermes Trismegistus, who is generally regarded as the Father of Alchemy, it is frequently mentioned as one of the old scientific problems. Readers of Scott's novel, "Kenilworth," may remember that Wayland Smith, in his account of his former master, Demetrius Doboobius, describes him as a profound chemist who had "made several efforts to fix mercury, and judged himself to have made a fair hit at the philosopher's stone." Hermes, or, rather, those who wrote over his name, speaks in the jargon of the adepts, about "catching the flying bird," by which is meant mercury, and "drowning it so that it may fly no more." The usual means for effecting this was amalgamation with gold, or some other metal or solution in some acid. To the ancient chemists mercury must have been one of the most interesting of objects. Its great heaviness, its metallic brilliancy, and its wonderful mobility, must all have combined to render it a subject for deep thought and an attractive object for experiment and investigation. Living in a warm climate, as they did, there was no means at their command by which its fluidity could be impaired. This subtle substance seemed to defy the usual attempts to grasp it; it rolled about like a solid sphere, but offered no resistance to the touch, and when pressed it split up into innumerable smaller globules so that the problem of "fixing" it must have had a strange fascination for the thoughtful alchemist, especially when he found that, on subjection to a comparatively moderate degree of heat, this heavy metal disappeared in vapor and left not a trace behind. I have often wondered what the old alchemists would have said if they had seen fluid mercury immersed in a clear liquid and brought out in the form of a lump of solid, bright metal. For, although this is not in any sense a solution of the problem, yet it is a most curious sight and one which was rarely seen before the discovery of the liquefaction of the gases. To Geber, Basil Valentine, Van Helmont, Helvetius, and men of their day, living in their climate, this startling phenomenon would have seemed nothing short of a miracle. In modern times the solidification of mercury had been frequently witnessed by these who dwelt in northern climates and by the skilful use of certain freezing mixtures made up of ordinary salts, it is not difficult to exhibit this metal in the solid state at any time. But it was not until the discovery of the liquefaction of carbonic acid, nitrous oxide, and other gases by Faraday, about 1823, that the freezing of mercury became a common lecture-room experiment.