358 THE SEAS 



order to prepare it for market this living tissue must be 

 removed, for it is only the skeleton which we use. The 

 fresh sponges are laid on deck and stamped upon or beaten ; 

 they are then strung together and hung over the side of 

 the ship to macerate for a day. They are once more taken 

 on deck and stamped upon, washed in tubs of sea water, 

 and hung up to dry. At the end of the week they are taken 

 ashore and spread on the sand to bake in the sun, 

 after which they are packed up in sacks ready for sale 

 (Plate 126). 



Salt 



In many parts of the world salt is obtained from the sea. 

 A thin layer of sea water is allowed to evaporate in the sun 

 and crystals of sea salt are deposited. In order that this 

 may be a commercial proposition it is necessary that the 

 summer should be long and sunny and the climate warm 

 and free from rain. This manufacture of sea salt or 

 " solar salt," is therefore confined to countries like Italy, 

 Spain, and the coasts of California. The sea water is run 

 into each of a series of shallow ponds in turn. The cry- 

 stallization of the salts present is not uniform, and as the 

 density of the water changes under evaporation the 

 composition of the salt deposited varies. By running the 

 water through a series of evaporating pools some of the 

 impurities are thus removed, and certain iron salts and 

 calcium carbonate and sulphate have been deposited before 

 the water passes into the main pool in which most of the 

 sodium chloride will crystallize. The finished product 

 however still contains impurities and may be refined by 

 recrystallization in fresh water. 



Sea salt contains a certain proportion of calcium and 

 magnesium chlorides which are very hygroscopic and 

 readily absorb moisture from the atmosphere. For table 



