General Distribution of Iodine. 323 



charge, are not very scrupulous as to the plants they employ, 

 and do not hesitate occasionally to add all vegetable matter which 

 comes in the way. It may therefore be objected to the statement 

 that forest trees contain iodine, that the iodine found in the pot- 

 ashes may be derived from succulent herbs and shrubs, and not from 

 the trees themselves ; but this objection will be at once removed when 

 it is stated, that in the lixivium of charcoal, I have found very 

 distinct traces of iodine. The charcoal sold and used in this country, 

 is principally oak, with a little beech, birch, elm, and ash ; and after 

 obtaining satisfactory evidence that the ashes of these woods burned 

 indiscriminately, contained this ingredient, I burned large quantities 

 of the first three kinds, viz., oak, beech, and birch, and treated the 

 ashes in the same way as the potashes. Iodine was distinctly pre- 

 sent in all three. The amount of iodine in forest trees must be com- 

 paratively small. When experimenting with potashes, one is apt 

 to forget the small bulk into which a large quantity of timber 

 falls, when the organic matter is expelled, and the saline ingredients 

 are alone left. So far as can be estimated from the present quali- 

 tative experiments, the relative quantity of iodine in forest trees is 

 much less than that in succulent plants growing in marshy places. 



The constant presence of iodine in potashes will lead to some 

 considerable alterations in the methods generally followed for the 

 detection of the former, by a process which necessitates the use of 

 the latter. The process for iodine in cod-liver oil, where potassa is 

 added to saponify the oil :* that for iodine in sea-water where po- 

 tassa is added to precipitate the alkaline earths :\ that for iodine in 

 coal where potassa is added to the ammoniacal liquor for the pur- 

 pose of fixing this element as iodide of potassium :\ and amongst 

 others, that for iodine in soils where potassa is added for the purpose 

 of more readily extracting the iodine from them,§ — must all be modi- 

 fied. 



For some time back I have also been engaged in collecting and 

 testing a large number of plants growing in different places. Al- 

 though it is now generally recognised, that iodine is a constituent of 

 some fresh water, and even a few strictly land plants, yet still the 

 volatilization of the iodine renders the success of such an investiga- 

 tion so uncertain, that the names of few plants have as yet been 

 published, in which iodine has been detected. The difficulty lies 

 principally in properly burning the plants to ashes. When iodide 

 of potassium is heated strongly alone, it volatilises, whilst if ac- 

 companied by carbonaceous matter, carbonate of potassa is formed, 

 and iodine vapour escapes. From experience, I feel certain that 



_ 



* De Jongh on Cod-Liver Oil, translated by Dr Carey. 



f Dr Schweitzer on the Analysis of Sea- Water as it exists in the English 

 Channel, near Brighton ; Lond. and Edin. Phil. Mag., vol. xv., p. 53. 

 \ M. Bussy ; Comptes liendus, tome xxx., p. 538. 

 § M. Chatin ; Comptes Rend us, tome xxxiv., p. 52. 



