Page:Popular Science Monthly Volume 43.djvu/97

This page has been proofread, but needs to be validated.

sels. But, before this process could be carried out in a practical form, the modern improvements in the process of distillation had to be discovered.

Similar processes to that mentioned by Alexander of Aphrodisias are described by Dioscorides and Pliny, in the first century a. d., for the preparation of two liquids so different as mercury and spirits of turpentine. These discoveries, also met in accidental observations, began to make more general the ideas of the industrial men and physicists of the time. Cinnabar, or sulphuret of mercury, has been used from remote antiquity as a red coloring matter (vermilion); the Romans got it from Spain, where the principal mines of mercury in Europe are still situated. It was early remarked that, in heating in an iron vessel to purify it, it disengages vapors of mercury, which are condensed on neighboring objects, chiefly on the cover of the vessel. This discovery was the origin of the regular extracting process, described by Dioscorides and Pliny. The cinnabar was placed in a capsule of iron in the middle of an earthenware pot. The cover was sealed on, and heat was applied. After the operation the cover was scraped, in order to detach and collect the globules of mercury which had sublimed from the capsule. Thus was obtained artificial quicksilver, which the ancients supposed to have different properties from natural quicksilver, or that which occurs in Nature in mines. This was an illusion, the mercury being identical, whatever the mode of extraction. At any rate, the process employed for the extraction of mercury by vaporization is the same as that described by Alexander of Aphrodisias for making sea-water potable; and this process, as I shall shortly explain, was the beginning of the alembic.

Another rudimentary process, the first that was applied to the extraction of an essential oil, is described by Dioscorides and by Pliny. It is for the distillation of pine resins, which are now called turpentines. They were heated in vessels over which wool was spread; this condensed the vapor; then the wool was pressed, in order to extract from it the liquefied product, spirits of turpentine, which was then called resin oil or flower of resin. It soon assumed an important function in the composition of the inflammable substances used in the arts and in war. But these terms seem at first to have designated also and at the same time the most liquid part of the resins, as well as the water charged with their soluble principles, which was floating on these resins like whey on milk, at the moment of their extraction; and, lastly, the distilled and odorous water which was vaporized at the same time with the essence. The ancients were in some confusion about these substances, which are distinct in modern chemistry; and this it is which makes the reading and interpretation of the old authors so hard.