36o THE SEAS 



it provides a clear gelatinous medium upon which cultures 

 of bacteria may be grown. 



Seaweeds contain certain chemical bodies the extraction 

 of which can be carried out on a commercial basis. In 

 Scotland the wrack that is swept up on the beach by the 

 waves is collected and burnt in kilns and iodine, bromine 

 and potash are obtained. Great care must be taken to 

 collect these weeds before they are rained upon as the fresh 

 water quickly washes out the iodine. For this reason 

 the harvesting and subsequent treatment of these weeds 

 is a summer industry. Iodine and potash are also obtained 

 from seaweed in other parts of the world and the industry 

 was much encouraged in America during the great war. 



A further substance, alginic acid, can also be extracted 

 from these weeds, and the substance hardens to form a 

 good insulating material. There are also many derivatives 

 of the acid which can be used for making size and for other 

 purposes. 



