290 THE MANUFACTURE OF KELP. 



are dried and used as fuel, the ashes being preserved on account of the iodine 

 they still retain, as well as the other salts. This process has not been 

 adopted probably because the manipulation, down to the burning of the 

 fuel into ashes, is a complicated labour, superadded to the ordinary process, 

 and with little advantage, for the ashes have still to be worked for iodine 

 and potash. The crushing of the weeds, and the drying of the crushed 

 cakes, present great practical difficulties, which those who have had any 

 experience in compressing fresh vegetables will fully appreciate. Dr. 

 Wallace's suggestion in the paper before referred to is more simple ; he 

 states that it is rather given to call attention to the subject than as a perfect 

 process. He wishes to supersede the present fused kelp by a loose charred 

 ash. He recommends the weed to be charred rather than burnt, and, as 

 this ash, from its bulk, would be inconvenient for carriage, that it should 

 be lixiviated with a small quantity of water, and the solution roughly eva- 

 porated to dryness. He says, " By this treatment a very ptire salt would be 

 obtained, the iodine would be wholly preserved, while the cost of working 

 would be more than counterbalanced by the saving of vitriol that would be 

 effected by the absence of the sulphur compounds." This idea meets some 

 of the difficulties of the question, but not all, the saving of iodine would to 

 a great extent be effected, it woidd make just the difference which now 

 exists between the best Highland kelp and that of the Channel Islands — 

 the former a vitreous mass, with more than half the iodine volatilised, the 

 result of igneous fusion — the latter a loose charred ash, the result of slow 

 combustion, at a low temperature, and containing much more of the iodine. 

 The difficulty, however, of completely charring on open slabs such a sub- 

 stance as seaweed, is considerable, and the salts resulting from its lixiviation 

 would be coloured by any portion not thoroughly carbonised. The Guernsey 

 kelp gives coloured solutions and dirty salts, which require recrystallisation 

 before they can be brought into the market. It may be remarked of Dr. 

 Wallace's suggestions, that they could not be carried out under cover, 

 except by elaborate arrangements, on account of the offensive smoke occa- 

 sioned by the products of combustion, which in his process are entirely 

 dissipated. 



My own researches were commenced by an estimation of the potash and 

 iodine in seven of the commonest species of seaweeds ; the results are 

 shown in the following Tables : — Nos. 1, 2, 3, 4, and 5, are the present 

 kelp-bearing species. Nos. 1 and 2, Laminaria digitata and Laminaria 

 saccharina are the general constituents of " drift weed," or " vraic venant " 

 of the Channel Islands. Nos. 3, 4, and 5, the Fucus vesiculosus, Fucus 

 serratus, and Fucus nodosus are generally the "cut weed," or "vraic scie," 

 of the Channel Islands. Nos. 6 and 7, the Zostera marina and Rhodomela 

 pinastroides, have not yet been employed in the manufacture of kelp. They 

 are exceedingly common all round the English coast, particularly the 

 south ; the latter has received no application, the former is largely used in 

 stuffing mattresses. 



The analyses are stated so as to show at a glance the relative value of 

 each weed for commercial purposes. The water is that driven off at 212°. 



