Sea-coal Facing
See COAL-DUST.
Sea-water is water impregnated with salt in solution. It is generally composed of chloride of sodium 2.50, chloride of magnesium 0.35, sulphate of magnesia 0.58, carbonate of lime and carbonate of magnesia 0.02, sulphate of lime 0.01, water 96.54.
It will be seen from the above why sea-water is utterly unfit for foundry purposes, as, in the subsequent process of evaporation, the chloride of sodium or common salt is deposited in innumerable crystals among the sand; and this deposit being volatile at furnace heat must flow as a slag immediately it is brought in contact with the molten metal. This explains why, where sea-water is employed, castings invariably show dull gray deposits on the surface, which utterly destroy all beauty of finish, and render them unfit for any but the commonest purposes. The slag produced is also a source of annoyance when the castings must be tooled. See SALT; DAUBING.