17C) 



BULLETIN OF THE BUREAU OF FISHKKIKS. 



From the following table given by Stanford, showing the quantity of iodine in 

 various seaweeds, the preponderating value of Laminaria for iodine manufacturing 

 will be apparent: 



Iodine in sun-dried seaweeds. 



Three methods of extracting iodine have been followed in Scotland, known as 

 the kelp process, the char process, and the wet process. The following accounts of 

 I hem are abridged from Stanford's report (1. a), and from Stanford's article in 

 Thorpe (1899): 



Kelp process. — This, the primitive method, is similar to that pursued for the 

 extraction of soda from rockweeds. It is unsatisfactory and wasteful, owing to the 

 fact that a large part of the iodine is lost by evaporation and a large part of 

 the remaining .substances are not utilized. One hundred tons of wet seaweed usually 

 make 5 tons of dried kelp, and, as only half of this is soluble. i'i tons are the actual 

 product of the labor of cutting, carrying, drying, and burning loo tons of raw weed. 

 The fused mass of carbon and ash resulting from the burning of the dried weeds is 

 lixiviated with water, and the solution is evaporated to remove the chlorides, sul 

 phates, and carbonates: the concentrated mother liquid is then treated with sulphuric 

 acid, the resulting sulphur and sulphates are removed, and the remaining acid liquor 

 is treated in a lead-lined retort with manganese dioxide, which, with the free sul- 

 phuric acid, liberates iodine; the iodine passes off in vapor and is condensed in a 

 series of earthenware receivers adapted to the retorts. The chemical reaction in this 

 case i~ as follows: 



2KI+MnO ! +2H s SO i =K a S0 4 +MnS0 1 +2H 8 0+2l. 



Char process. — This has for its object the prevention of loss of valuable material 

 by volatilization and decomposition, and consists in heating dry seaweed in iron 

 retorts or brick ovens. The tangle swells in the retorts and is converted into a very 

 porous charcoal, from which the salts arc readily washed. This charcoal is reported 

 to lie an efficient decolorizer and deodorizer. The superiority of the char process 

 over the kelp process will be seen from the following comparison of the results of 

 treating four tons by each process: 



Kelp 

 process. 



Char 

 process. 



Crude product pounds.. 1,500 3,000 



Per cent of dried weed L8.7 37.5 



Salts recovered pounds.. 657 877 



iodine produced <ir> IS. 27 29.25 



Loss of salts pounds.. 



I..." of iodine do. 



Loss hi ^jilts per ton of tangle, .do. 

 Loss of iodine per ton of tangle., do. 



