A marine production of a remarkably porous and absorbent nature. Its property of readily imbibing almost as great a volume of water as its own bulk, and as readily parting with it by compression, renders it of great utility. The best is of a light colour, free from stones and other impurities, very soft and elastic, and the pores or holes small. It is chiefly obtained from the Mediterranean, about the shores of Turkey and the Archipelago, where it grows upon the rocks at considerable depths under water. To bleach sponge and render it white, it is soaked repeatedly in fresh water, changing the fluid several times a day; and at the end of five or six days it will be ready for bleaching. If the sponge contains pieces of shells, chalk, etc, which cannot be extracted without tearing it, the sponge must be soaked for twenty-four hours in muriatic acid, diluted in twenty times as much water, which will cause an effervescence to take place, and carbonic acid to be liberated, when the shells and chalk will be dissolved. After this the sponge must be carefully washed in fresh water, and then immersed for seven or eight days in a weak solution of sulphuric acid (specific gravity 1.024), occasionally pressing it out dry.
After it has again been perfectly washed and cleaned, it may be sprinkled with a little rose-water, to give it a pleasant smell.