GrALLOWAY — On Iodine and Bromine from Kelp. 153 



the decomposition of the hyposulphites, has completely deposited, the 

 clear liquid is drawn off into the iodine still, and the manganese per- 

 oxide is then added to it. 



When this process first came into operation, bromine had not been 

 discovered in the ash of sea-weed ; even the late Dr. Anderson, in his 

 well-known and often quoted analyses of the ash of sea- weed, does not 

 give it as a constituent. New analytical investigations of the ash of 

 the various sea plants are wanted ; the plants ought to be carefully 

 freed, before incineration, from all adhering salt water, so that the 

 quantities of chlorine, bromine, and iodine they naturally contain 

 might be correctly ascertained. The investigation would lead, most 

 probably, to the discovery that there are, properly speaking, bromine 

 as well as iodine producing plants. 



The three metalloids are each liberated from their metallic combi- 

 nations by the manganese peroxide and sulphuric acid, but owing to 

 their different degrees of affinity for metals — chlorine having the 

 strongest, and iodine the weakest affinity — the latter is the first set 

 free ; but it requires the greatest care and attention to prevent some 

 portion of the other two fi'om being set free at the same time. If 

 this occurs, they enter into union with one another, forming volatile 

 compounds which affect the eyes, and have a very pungent odoui'. 

 The liberation of the bromine or chlorine, or both, during the extrac- 

 tion of the iodine may occur, for instance, from the manganese oxide 

 becoming unequally diffused in the liquid ; they will also be liberated 

 if the temperature of the liquid becomes too high ; and it appears to 

 me highly probable that the influence of mass will also cause their 

 liberation, especially when the quantity of iodine becomes, by volati- 

 lization, much decreased in quantity. That they are liberated to some 

 extent during the distillation of the iodine is at once perceived by 

 those who visit the still during the distillation, and who are ac- 

 quainted with the properties of these compounds. I may here observe 

 that the still-man judges whether at least an undue proportion of the 

 other two are volatilizing by the colour of the vapour ; if it is of a 

 brownish or whitish colour he is aware he is losing iodine. When the 

 distillation is finished, and the still head removed, the vapour which 

 escapes from the still has always a violet colour, and some iodine 

 always remains in the liquid ; for if the distillation were continued 

 until all the iodine had volatilized, there would be evolved along with 

 it in the last stages one or both of the other metalloids in somewhat 

 large proportions ; and consequently there would be a loss instead of 

 a gain in iodine. These are some of the imperfections and difficulties 

 of Wollaston's process. 



The extraction of bromine follows the extraction of iodine, the 

 same process being adopted, and similar precautions have to be ob- 

 served. 



It is evident such a process is unsuitable for the extraction of 

 valuable substances like iodine and bromine, and it may also be ob- 

 served that the liquid from which they have been volatilized has to 

 be thrown away, on account of the difficulty of utilizing it, although 



