THE BROWN ALGAE-ALGIN FROM KELPS AND FUCOIDS 99 



weed is then washed with fresh water to remove soluble materials (laminarin, 

 mannitol, salts) and any remaining calcium chloride until the waste waters con- 

 tain less than 0.5 per cent soluble matter. Next the seaweed may be washed 

 with a dilute hydrochloric acid solution to dissolve any residual alkaline earth 

 salts. The acid in turn is eliminated by further washing with fresh water. 



Then the seaweed is digested with double its volume of a warm 4 per cent 

 soda ash solution. The mass is agitated simultaneously with pulp beaters until 

 the seaweed is comminuted. It may also be vigorously agitated by compressed 

 air pumped through perforated pipes or porous diffuser plates. 



The mass is diluted with twice its volume of water by constant vigorous agita- 

 tion. This produces an emulsion which is pumped into a settling tank. After 

 about 10 hours the cellulose particles flock together and rise to the top, forming 

 a compact, floating cake. The underlying liquid contains crude sodium alginate. 

 This liquor is decolorized by intimate mixture with a jelly composed of colloidal 

 hydrated alumina (or aluminum hydroxide), silica gel, and aluminum alginate. 

 The amount of absorbent jelly used is approximately equivalent to one-fourth of 

 the dry weight of the sodium alginate present. The pigments are selectively 

 adsorbed by the jelly, which is later removed by centrifuging. 



The crude sodium alginate solution is then clarified, usually by filtration. The 

 clarified solution is then treated with hydrochloric acid to precipitate the alginic 

 acid. The crude alginic acid is collected and then dewatered in a basket cen- 

 trifuge. After a final washing with alcohol to purify it further it may be dried at 

 140° to 160° F (60° C to 71° C) and packed for shipment, or it may be con- 

 verted into sodium or another alginate by treatment with the proper carbonate, 

 oxide, or hydroxide. 



Laminarin, the "phaeophycean starch", may be obtained as a by-product of 

 the manufacture of algin from Laminaria. The dilute solution of calcium chloride, 

 which is used to treat the crude Laminaria, dissolves laminarin, mannitol and 

 various salts from the seaweed. To recover laminarin from this liquor it is 

 evaporated to a relatively small volume. Alcohol is added to the concentrated 

 solution in an amount sufficient to make up 85 per cent, thus completely pre- 

 cipitating the laminarin. After it has been separated from the solution, the 

 laminarin may be purified by dissolution in dilute calcium chloride solution and 

 reprecipitation with alcohol. 



Uses of Alginic Acid and Alginates 



Industrial Uses. Alginic acid as such is comparatively limited in its applications. 

 It can easily be molded into any desired shape while wet and retain its form 

 when dry, assuming a hard, hornlike form that is very insoluble and resistant to 

 the action of chemicals. 



The properties of the various alginates indicate many uses (Table 21). Sodium 

 alginate is the most versatile of the alginates since it is easily soluble in water 

 and can be readily made into insoluble substances. As a valuable sizing material, 

 it is sometimes used as an adjunct to starch because it fills the cloth better and 

 is tougher and more elastic. Moreover, it is transparent when dry. It imparts a 

 thick, clothy, elastic feeling to goods, without the stiffness of starch. Since its 

 solutions are so viscous, it goes further than starch or any gum. Once the sodium 

 alginate has impregnated the cloth it may easily be made insoluble by treatment 



