ALGAL UTILIZATION 447 



the weed is leached first with acid and then treated with soda ash 

 or sodium carbonate solution. The final product can be pure alginic 

 acid but more usually it is the calcium or sodium salt that is pre- 

 pared. The alkali salts dissolve in water to give a thick, viscous 

 hquid and this can be spun into an artificial silk thread. The final 

 yarn is usually of calcium or sodium alginate. These yarns are 

 soluble in soap and soda and advantage has been taken of this in the 

 production of special weaves of mixed alginate and other fibres, 

 because subsequently the alginate can be dissolved out: this is 

 known as the 'disappearing fibre' technique. Resistant threads can 

 be obtained by replacing the calcium or sodium with chromium or 

 beryllium. In practice it is found easier to weave the yarn in the 

 form of calcium alginate and then convert the woven material to 

 beryllium or chromium by immersing it in a bath of beryllium or 

 chromium acetate. 



The alginates of the heavy metals are not soluble in water and 

 they form a plastic material when wet that sets hard on drying. 

 Algin has a variety of other uses, apart from the production of 

 plastics and artificial fibres. Among the more important is its use as 

 a stabilizer in ice-creams and sherbets, as a filler to candy bars and 

 in salad dressings. It can also be used as a thickening and poHshing 

 material and the insoluble salts have been used in the production of 

 water-proof cloth. More recently experiments have been conducted 

 to ascertain its usefulness as an ameliorator of poor soil conditions. 

 In this respect it will be a competitor with materials such as kril- 

 lium which merely alter the physical state of the soil. 



Apart from algin the other major seaweed industry today is con- 

 cerned with the production of agar-agar, the material that is used in 

 culturing bacteria and fungi. A large number of genera and species 

 are used as the source of this material and such plants have been 

 termed agarophytes. For many years up to 1939, Japan had been 

 the principal producer of agar, about 2,000 metric tons being pro- 

 duced annually. Whilst a number of red algae have been and still are 

 used for this purpose in Japan, the principal source is Gelidium 

 amansii. After the weed has been collected it is bleached and then 

 boiled. This extracts the gelatinous material which, after straining, 

 is purified by freezing, the water flowing off with the impurities 

 when it is thawed. 



When Japan entered the last war, the world's supply of agar was 

 cut off. Since agar was urgently needed for pathological work, all 



