CHAPTER 6 

 The Brown Algae— Algin from Kelps and Fucoids 



Most of the masses of seaweed along the shores of North America and Europe 

 are brown algae. The two principal genera are Laminaria, which is usually found 

 in deep water, and Fuciis, which commonly grows on the rocks between the tidal 

 levels. 



Formerly, great quantities of Laminaria and giant kelp (chiefly Macrocystis 

 pyrifera) were burned and the ashes used for the production of iodine, iodides, 

 and potassium salts. Since this industry is no longer of considerable commercial 

 importance, it will not be described in this chapter; however, a detailed de- 

 scription of methods formerly used may be found in the first edition of this book. 



After the kelp-burning industry ceased to exist, the principal commercial use 

 of brown algae has been the manufacture of algin and its derivatives (i.e., its salts 

 and esters). In 1883 this industry was started by Stanford (1883, 1884, 1886), 

 who noticed that a viscous liquid formed in sacks contained in the fronds of 

 certain Laminaria when they were soaked in fresh water. When this liquid was 

 expressed and evaporated, a substance resembling albumen resulted; it was only 

 slightly soluble in pure water but easily soluble in water containing a small amount 

 of sodium or potassium hydroxide or carbonate. Stanford named this colloidal 

 substance, which was soluble in dilute soda solution, algin or alginic acid. He 

 recognized its commercial possibilities and carried out extensive experiments to 

 determine the properties and possible uses of alginic acid and alginates. Later he 

 manufactured it on a commercial scale in Scotland. The factory was not com- 

 mercially successful at that time, but more recently the manufacture of algin has 

 become an important industry, both in the United Kingdom and the United States. 



The Chemical and Physical Properties of Algin and Sodium Alginate 



Alginic acid, or algin, is an organic acid which occurs in large quantities in 

 many seaweeds having the composition of 42.0 per cent carbon, 4.5 per cent 

 hydrogen, and 53.4 per cent oxygen. It is very slightly soluble in cold water, 

 slightly soluble in boiling water, and insoluble in alcohol, ether, and glycerol. 

 Moist alginic acid is capable of absorbing 10 to 20 times its weight of water. 

 When moist, it is readily soluble in dilute alkali; but, when dried, it becomes very 

 hard and horny and resistant to solvents. Dried alginic acid can be turned on a 

 lathe. 



If a solution of sodium alginate is acidified with a strong mineral acid, it 

 liberates free alginic acid, which, being insoluble in water, precipitates as a white 

 gelatinous mass. Sodium alginate in solution is coagulated by ethyl and methyl 

 alcohol and acetone. 



Sodium alginate solutions are transposed by solutions of the salts of the follow- 

 ing metals, insoluble alginates being formed: cobalt, copper, platinum, nickel, 



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