665 



as yet been mostly directed to the atmosphere and to rain-water ; and 

 he considered that a notice of the results obtained might be interest- 

 ing to the Society, alike from the intimate connexion which exists 

 between the plant and the atmosphere, and from the fact that he has 

 been led to look for, and to detect, the presence of iodine in a depart- 

 ment of the vegetable kingdom in which it has not formerly been 

 observed, 



Chatin has not published a detailed account of the processes 

 adopted by him ; but, from the manner in which he speaks of the 

 good eflfects produced by the addition of potash to substances under 

 examination, which, to use his own words, " arrested the complete 

 decomposition of the iodine compounds, whilst the waters were eva- 

 porating," and by the addition of carbonate of potash and carbonate 

 of soda, which " rendered the iodine present in soils much more easily 

 extracted," the author was led to believe that the fixed alkalies had 

 been largely employed by him. Accordingly, in the first experiments 

 the alkalies were used in their caustic condition, for the purpose of 

 fixing any free iodine, and retaining any compound of iodine, which 

 might be encountered. 



Mr. Macadam commenced vs^ith an examination of the atmosphere. 

 By the arrangement he employed, the air was made to traverse— 1st, 

 a tube containing slips of paper which had been previously dipped in 

 a solution of starch; and 2ndly, a double-necked gas-bottle, contain- 

 ing about three ounces of a dilute solution of caustic soda. A con- 

 tinuous stream of air was drawn through the arrangement for some 

 hours. This experiment was conducted in the morning ; and in the 

 afternoon a stream of air was for several hours drawn through the 

 same arrangement, caustic potash being substituted for the caustic 

 soda. The stai'ch-papers did not exhibit the slightest colouration, 

 even when moistened with distilled water. The solutions of potash 

 and soda, however, on being treated with starch and nitric acid, at 

 once exhibited the rose colour characteristic of the presence of iodine 

 in small quantity. So far the experiments seemed to lead to the de- 

 sired conclusion ;' but when portions of the original alkaline solutions, 

 which had not been subjected to a current of air, were carefully tested, 

 it was found that iodine was present in them, in quantity, to all ap- 

 pearance, as great as it was in those portions which had been used in 

 the experiments. 



Wishing to trace back the iodine to its source, samples of the car- 

 bonate of potassa, carbonate of soda, and lime-shell which had been 

 employed in the preparation of the caustic solutions, were analyzed, 

 VOL. IV. 4 Q 



