80 



MARINE PRODUCTS OF COMMERCE 



very little change in other properties. Temperature of gelation is controlled by 

 concentration of the solute, with gel strength determined by which solute is em- 

 ployed. 



80 



70 



60t- 



to 

 o 



§50 

 u 



(0 



40 



30 



20 



RELATIVE VISCOSITY OF 

 HYPNEA AGAR 



A-HYPNEA, l%,NO SALTS ADDED 

 B-HYPNEA, l^i.WITH .2^. KCL 

 C-SAME, WITH .6H KCL 

 D-GELIDIUM AGAR, I J; 

 E- DISTILLED WATER 



80 70 60 50 



DEGREES C. 



40 30 



Fig. 5-13. Relative viscosity of Hypnea agar. 



There is still much to be learned about the behavior of the Hypnea extractive, in 

 particular, and about physical phenomena of phycocolloids, in general, especially 

 those exhibited by the Hypnea extractive to an unusual degree. 



Chemical Nature of Agar. That agar is a sulfuric acid ester of a linear galactan 

 is generally accepted by chemists who have investigated its structure in recent 

 years. According to Jones and Peat (1942), whose work is widely accepted, agar 

 consists of a chain of 9 cf-galactopyanose residues attached by 1,3 linkages, and 

 terminated at the reducing end by one Z-galactose residue. The great com- 

 plexity of the chemical structure of agar still puzzles chemists; in fact, Percival 

 and Thompson (1942) expressed the opinion that Jones and Peat have over- 

 simplified the structure of agar in their conclusions. Percival and Thompson main- 

 tain that the theoretical methoxyl content of methylated agar of the formula 

 proposed by Jones and Peat would be 42 per cent, whereas the highest observed 

 value does not exceed 35 per cent. Barry and Dillon (1944) examined agar pre- 



