1748 MANURES AND MANURING 



On the Pacific Coast of the United States large quantities of kelp are 

 harvested annually (i). The writer points out that a certain amount of 

 waste is incurred by not recovering the iodine and bromine contained in 

 the kelp. These elements being more valuable for chemical or pharmaceu- 

 tical uses than for agriculture, their extraction would seem advisable espe- 

 cially as their recovery would enable the manure to be sold at a lower 

 price. 



The extraction of potash salts from seaiveed. — The seaweeds used for 

 this purpose consist of Macrocystis spp., Nereocystis spp. and Pelagophycus 

 spp. which form the " giant kelp " of the American Pacific coast, and Lami- 

 naria flexicaulis, L. Cloustoni, L. saccharina, Saccorhiza bulbosa which are 

 found in Europe. The average chemical composition of fresh European 

 seaweed is as follows : 



Water. ... 85 % 



Mineral matter 7 % 



{ Chlorides . . 3.85 % 

 Dry matter . 15 % \ . / Potash salts . 4 % ) Iodide ... 0.13 % 



Organic matter 7 % 



; 



other salts. 



f Bromide . . o.oi 



7 Chlorides, 

 ,, * phosphate 



sulphates, 

 sphates of sodium, 

 magnesium, calcium, 

 iron, manganese. 



Every year about 100 000 tons of fresh .seaweed are gathered in France 

 and 250 000 tons in the United Kingdom and Norway. From the 350 000 

 tons tlie following products are obtained : 175 tons of iodine, 7000 tons of 

 potash salts, 15 000 tons of soda ash. B3' improved methods of manu- 

 facture the yield of iodine and potash salts might well be doubled and at 

 the same time 10 000 tons of mineral salts other than potash, 175 tons of 

 bromine and 28 000 tons of raw algin could be produced. With the use 

 of cutters the seaweed harvest could also be increased. 



The potash salts, which consist chiefly of the chloride, make up about 

 4 per cent of the fresh seaweed or 25 per cent of the dry matter. They are 

 extracted by lixiviating the kelp, or may be obtained as an efflorescence 

 on drying the seaweed by heat. The latter process yields a substance con- 

 taining 65 per cent of potassium chloride (41 per cent of KjO) which may 

 be used as such for manure or siibjected to purification as in the case of 

 Stassfurt salts. 



Other salts extracted by lixiviation. — These make up 43 per cent of 

 the total salts, 3 per cent of the fresh seaweed or 20 per cent of the dry 

 matter. They consist of about 50 per cent of sodium chloride, and 50 per 

 cent of the other salts, and though much less valuable as feitilisers than 

 the potash salts, they are used for that pitrpose in France. 



(i) .See R. 1912, No. 1147 ; K. 1914, No. 212 ; R. 1915, Nos. 467 an) 688. (Ed.) 



