I I I LIGATION i»F SEAWEEDS IN THE UNITED STATES. 



177 



Wet process. — Air-dried tangle is boiled with a solution of sodium carbonate, 

 and the mass is filtered. The precipitate is composed largely of cellulose, while 

 the filtrate contains, besides the salts, a peculiar gummy substance, algin. When the 

 filtrate is treated with sulphuric acid, algin is precipitated. The solution, after the 

 removal of algin, is neutralized with calcium carbonate? evaporated, the easily crys- 

 tallized salts are removed, and the mother liquor is treated for iodine in the usual 

 maimer. 



This process is the most economical, in that it increases the yield of salts and 

 iodine and reduces the cost by the production of algin and cellulose. The compara- 

 tive value of the three processes may be readily appreciated from the following table, 

 the figures being on a liasis of Inn tons of dry tangle: 



ItoTUS. 



Kelp 

 process. 



Char Wet 



pi ss process 



in\ n 1 utilized I per rem 



i !rude product (tons) 



Salts extracted I tons I. 



[odine extracted poun 

 Residuals 1 1< »ns > : 



Kelp un<h- i valueless i - 



Charcoal 



Tar; ammonia 



Algin 



Cellulose 



Dextrin, etc 



18 



is 



9 



•JTll 



36 70 



36 • «33 



15 20 



him 600 



3i ; 



,x 



20 

 15 



" Water extra,-!. 



Writing of the Scotch iodine industry. Stanford (I. e.) noted that the •"drift 

 kelp", the only kind now used in making iodine, consists of two species of Lami- 

 naria, which are always submerged and are torn tip by the. violent gales so 

 common on the west coast. In Ireland the plants are sometimes cut under 

 water with long-handled hooks. These plants are much damaged by rain or fresh 

 water and are often, after drying, almost valueless, but if properly cured they 

 contain ten times as much iodine as the rock weeds. 



OTHER USES OK THE KELPS. 



The collateral substances produced during the extraction of iodine by the wet 

 process deserve consideration on account of their prospective value in the arts. 

 These substances are algin. cellulose, dextrin, and mannite, in addition to the 

 various salts elsewhere referred to. The following account of algin and its com- 

 pounds is adapted from Stanford (lss4), by whom this substance was discovered: 



It the long iron, Is ,,f the Laminaria [digitata] he observed after exposure to rain, a tumid appear- 

 ance will be noticed, ami sacs of llui,l arc formed from the endosmosis of the water through the 

 membrane, dissolving a peculiar glutinous principle. If the sacs lie cut, a neutral, glairy, colorless 

 fluid escapes It may often he ^n-n partially evaporated on the frond as a colorless jelly. This 

 substance, which is then insoluble in water, is the remarkable bodyto which has been given the name 

 of Algin. The natural li,|iii,l it-elf is miscible with water, but coagulated by alcohol and by mineral 

 acids, It contains calcium, magnesium, and sodium, in combination with a new acid, which is called 

 alginic acid. When this natural liquid is evaporated to dryness it becomes insoluble in water, but it 

 is very soluble in alkalies. This new substance is so abundant in the plant that on maceration for 

 twenty-four hours in sodium carbonate in the cold, the plant is completely disintegrated. The mass 



B. B. F. 1VKM— 12 



