In Italy most of the salt is made by solar evaporation. The salt grounds, which occupy extensive areas, are furnished with reservoirs for the preparation of the sea-water by saturation and for the deposit of salt. The former are known as condensers and the latter as crystallizing beds, and in both the work is carried on by solar evaporation only. Every salt-ground, or salt-garden, as it is called, has a feeding channel for the inflow of sea-water, a drainage channel, and a network of internal channels at low and high levels, as are required for immission or drainage purposes. In Portugal and Spain, salt is made by solar evaporation from sea-water, and although there are differences between the several methods, they apply only to details regarding the areas of the salt-grounds or the sizes of the reservoirs. Let it be clearly understood that all commercial salt is produced either from the sea or from rock-salt. Sea-water is evaporated to precipitate its salt either by the heat of the sun or by artificial heat. Rock-salt is mined and refined for market purposes, and it is resolved into brine from which the salt is extracted by solar heat or the process of boiling, but whether the salines are obtained from salt lakes or from natural brine springs, or are prepared by flooding salt deposits with water and pumping it out in the form of fully saturated brine, rock-salt is the foundation for them all. And in all the processes of manufacture the basic principle is the same, and consists of applying heat to drive off the liquid which contains the salt and collecting the crystalline deposit which remains. The principle of what is described as the boiling process is fundamental and unalterable, and for thousands of years the plant and utensils employed in the process underwent no material change. Since the sixteenth century in England, variations in the shape, size, and capacity of the pans have been introduced, and experiments have been made in the re-arrangement of the receptacles and redistribution of the furnaces, while coal fuel has been substituted for straw and wood, but it is only in the past twenty-five years that any material success has been achieved in the matter of economizing and accelerating the process of production, controlling the heat in order to regulate the grain of the salt, producing more than one grade of salt in one operation, or of automatically and continuously collecting the salt as it is precipitated from the brine. The earliest exact and detailed description that we have of salt-making appears in _De Re Metallica_, a famous work by Georgius Agricola, of Saxony, which was published in 1556, and which for the following 180 years, remained the standard text-book on mining and metallurgy. In Chapter XII of this work, the preparation of which occupied Agricola for a quarter of a century, he gives the exhaustive particulars relating to the boiling process from which the ensuing account is compiled.