SOME ALGAL, GELATINES. 7 



it promises to be a valuable product. It may possibly find use in the 

 preparation of certain food products. 



A small sample of an unidentified seaweed just received from Key 

 West. Fla. (1920), yields a larjjje amount of a soft, transparent, very 

 elastic jelly, very difi'erent from anj^ of the jellies examined so far. 

 Quantitative determinations and a stud}^ of its properties have not 

 been made. 



ALGINIC ACID. 



The examination of a larn;e number of seaweeds brought out the 

 general conclusions (1) that the gelatinous products related to gelose 

 are confined to the group of red seaweeds; (2) that the green sea- 

 weeds yield little or no gelatinous products, and (3) that the brown 

 algae produce a gelatinous substance ver}'^ different from gelose. The 

 gelatinous principle of the brown algae is known as alginic acid or 

 algin. and was first isolated from the kelp Laminaria by E. C. C. 

 Stanford (Journal of the Society of Chemical Industry, Vol. Ill, 

 No. 5, 1884, pp. 297-303 ; A'ol. IV^, No. 9, 1885, pp. 518-520, 595 ; and 

 Journal of the Society of Arts, Vol. X, No. 481, 1862, pp. 185-199). 

 His method was to macerate the dried kelp in water to remove the 

 water soluble matters, which amount to about one-third of the dry 

 weed. The insoluble residue contains in part the alginic acid which 

 is rendered soluble by digestion in a hot dilute solution of sodium 

 carbonate. It dissolves out as sodium alginate. This is filtered out 

 with difficulty, and the alginic acid is precipitated by treating the 

 filtrate with hydrochloric acid. The precipitate separates out as an 

 amorphous substance of light amber color, which is washed and 

 bleached. When dry the alginic acid resembles albumen or horn. 

 It is insoluble in either cold or hot water. 



Soluble algin or sodium alginate is produced when alginic acid is 

 allowed to react with a solution of sodium carbonate. According to 

 Stanford, a solution of soluble algin has 14 times the viscositj^ of 

 starch and 37 times that of gum arable. The alginic acid is precipi- 

 tated from the solution of its sodium salt by most mineral acids and 

 by picric, oxalic, tartaric, and citric acids. A 2 per cent aqueous 

 solution becomes semisolid when acidulated with hydrochloric acid. 

 Insoluble alginates are formed with most metallic salts, some of them 

 being of curious composition. 



Soluble algin differs from gelose by containing nitrogen and not 

 gelatinizing on cooling. 



Because of its property of combining with various elements with 

 the production of numerous compounds possessing various degrees 

 of solubility and viscosity, alginic acid promises to become an im- 

 portant commercial product used in the preparation of waterproof 

 fabrics and of pastes for the thickening of colors in the printing and 

 sizing of cloth. 



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