THE MANUFACTURE OF KELP. 289 



The disadvantages of the present method are principally the fol- 

 lowing : — 



1st. The high temperature developed in burning, by which much of the 

 iodine is volatilised, and some of the potash ; the loss of iodine is equal to 

 the present yield. 



2nd. The high temperature also enables the carbon to deoxidise the 

 alkaline sulphates, reducing them to sulphites, hyposulphites, and sulphides. 

 These become concentrated in the mother liquor, remaining after the ex- 

 traction of the salts, and entailing a large expenditure of oil of vitriol for 

 their reconversion into sulphates. Dr. Wallace (in a paper read before the 

 British Association, at Aberdeen, September 14, 1859), estimates the cost of 

 extracting all the salts and the iodine from kelp, at from 25s. to 28s. per 

 ton, of which from lis. to 13s. are expended in oil of vitriol. The import- 

 ance of this disadvantage is therefore obvious ; the addition of the oil of 

 vitriol to the mother liqiior sets free large volumes of sulphuretted hydrogen, 

 a noxious gas, very difficult to get rid of, resulting from the decomposition 

 of these sulphur compounds. To such an extent is this deoxidation carried, 

 that kelp prepared from the Fuci, which are rich in sulphates, gives off 

 sulphuretted hydrogen on simple solution in water. 



3rd. The crude manner in which the weed is burned in a rough clay 

 pit, or in heaps on the beach, the kelp thus becoming mixed with the clay, 

 sand, or stones, which are sometimes also employed as adulterations to the 

 extent of 50 per cent. 



4th. The general neglect of the winter supply, on account of the diffi- 

 culty of drying the weeds at that season. This consists principally of the 

 deep sea algae, torn up by storms ; it occurs in the greatest quantity, and 

 is also much the richest in iodine and potash. Yet this is almost entirely 

 lost. Even in the summer, during a wet season, large quantities of drift 

 weed collected by the helpers are rotted by the rain, and rendered useless 

 for burning ; and this, says Mr. Paterson, "■ was the fate of many thousands 

 of tons during the last kelp season." 



5th. The entire loss of the heat produced, and the products of com- 

 bustion. 



6th. The dense smoke and unpleasant odour evolved in burning, 

 banishes the kelp burner to desolate shores, and, consequently, increases 

 the distance of the lixiviating factory ; the ash in its long transit suffers 

 much by exposure to rain ; and the residuum of lixiviation, a valuable 

 manure in the country, is a bye product in a city. It may be urged, also, 

 that the poor helpers in their arduous work, receive but a small part of 

 the real value of their labour. These evils have been frequently urged, and 

 are universally admitted ; some reforms have even been proposed. 



Dr. Kemp has suggested a process, which consists in selecting the stems 

 of those algaa which are the richest in iodine, and crushing them ; they are 

 then set by in a tank for a few days, and the most soluble salts, including 

 the iodides, extracted by cold water acidified with hydrochloric acid. The 

 solution is then treated with chloride of lime, and the iodine thus set free 

 precipitated by amido-acetate of lead. The cakes of weed left after pressure 



VOL. II. x 



