Even in this country, when the old open-pan system of evaporating salt from brine produced only two tons of salt for the consumption of a ton of fuel, rock-salt could be raised, purified, and marketed in competition with white salt, but the modern boiling processes have effected such substantial improvements and consequent economical advantages, that the rock-salt industry appears to be doomed to decay. Rock-salt, as quarried from its native bed, is found in many variations of colour, from grey and yellow to green and brick red, according to the nature of the impurities of the locality in which the deposit lies, and such salt must be cleansed from all traces of iron, clay, gypsum, or bitumen before it is fit for domestic use. Many processes have been experimented with for the removal of impurities. One of the most plausible methods was based on the fact that salt fuses at a temperature of about 1,750 degrees, and the theory was to remove all impurities from the fluid mass by the agency of compressed air. The principle was unsuccessfully experimented with in Würtemberg nearly half a century ago, but a modern adaptation of the process claimed to be more successful. The molten material, in this case, ran into rotating pans and gradually overflowed; and it was then shovelled into another receptacle and, while subjected to the action of compressed air, raised by small buckets to a certain height and emptied into inclined screens, through which it was automatically graded. It was claimed that from the time of casting the crude material into the furnace, until the perfect white salt appeared, the process occupied only fifteen minutes, and that rock-salt could be broken in the mine, transported, fused, and packed ready for table use in less than two hours.