IODINE AND OTHER CHEMICALS 71 



kelp. This process has been described above. The 

 kelp residue (un fermented leaves) was treated with 

 washing-soda solution until the leaves were disinte- 

 grated; then the solution was filtered and acidified. 

 The acidification precipitated the alginic acid, which 

 was separated by filtration. Sodium alginate was 

 prepared by treating the alginic acid with soda. 



The preparation of alginic acid is now carried on 

 in connection with the manufacture of iodine and 

 potash from laminaria and fuci in Ireland. The 

 laminaria are macerated for twenty-four hours with 

 one tenth of their weight of washing-soda. This con- 

 verts the algae into a very viscous, semigelatinous 

 mass, which must be heated before it can be filtered 

 through coarse bags. The alginic acid is separated 

 from the solution by the addition of a mineral acid, 

 and is obtained in a compact cake resembling new 

 cheese. Algin may be sold in this form, or it may be 

 converted into sodium alginate. 



The filtrate from the alginic acid is evaporated 

 and burned. Potassium salts and iodine are obtained 

 from the ash according to the method described 

 elsewhere. 



Alginic acid may be molded while wet and retains 

 its form when dry. In this way it can be made into 

 many useful articles, which are hard and horn-like, 

 insoluble in water, resistant to the action of chemi- 

 cals, and of high dielectric strength. 



Sodium alginate is one of the most useful of the 

 alginates, as it is soluble in water, but can be easily 

 converted into either alginic acid or insoluble algi- 

 nates. It is a valuable sizing material, as it imparts 



