31 8 The Commercial Products of the Sea. 



Marine plants afford a large revenue for the manufac- 

 ture of kelp and iodine. Kelp is prepared by burning the 

 dead weeds till they are reduced to hard, dark-coloured 

 cakes, in which state it is sent to market. Kelp is the 

 only commercial source for the production of iodine, and 

 its immense value in photography and in medicine has 

 given an impulse to the manufacture of kelp, which 

 renders it by far the most important of all the applications 

 of seaweed. The average yield of iodine in Scotland from 

 a ton of driftweed kelp is about five pounds. 



The proportion of iodine in sea water appears to be 

 VQvy small, and it would require more than 30,000,000 

 pounds of sea Avater to furnish the marine algae with one 

 pound of iodine. 



The production of kelp in the United Kingdom 

 amounts to about 10,000 or 11,000 tons; the manufacture 

 is carried on in Ireland, the Western Islands, and Orkney 

 and Shetland. In France there are many large factories 

 at Granville, Cherbourg, etc. 



The manufacture of iodine is chiefly confined to Great 

 Britain and France, for very little is produced in any other 

 countries. It was attempted on the American coasts of 

 the Atlantic, but the weed was found to be of too poor a 

 quality. The average production of iodine is about 10 lbs. 

 to the ton of kelp, and as it requires 20 tons of wet weed 

 to produce one ton of kelp, the total quantity made repre- 

 sents the burning of 400,000 tons of seaweed annually. 

 At the present price the iodine produced is of more value 

 than the alkaline salts, wdiich were the original object of 

 the industry. 



Carrageen Moss. — One of the best known of the algae 

 in commerce is the CJiondrns crispus, the source of carrageen 

 or Irish moss, which is sometimes employed as a substi- 



