232 Botanical Society of Edinburgh. 



iodine compounds whilst the waters were evaporating," and by tht 

 addition of carbonate of potash and carbonate of soda, which " ren- 

 dered the iodine present in soils much more easily extracted," the 

 author was led to believe that the fixed alkalies had been largely em- 

 ployed 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 with 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 2nd, a double-necked gas bottle, 

 containing about 3 oz. of a dilute solution of caustic soda. A con- 

 tinuous stream of air was drawn through the arrangement for some 

 hours. This ex{)eriment 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 starch-papers did not exhibit the slightest coloration, 

 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 v/as found that iodine was present in them, in quantity to 

 all appearance 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 

 carbonate of potash, carbonate of soda and lime, which had been 

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

 and in all three iodine was present in perceptible quantity. Desirous 

 of making certain that the reagents used in the investigations were as 

 pure as other commercial substances of the same kind, various speci- 

 mens were procured from different sources, and in every sample which 

 was subjected to examination the presence of iodine was detected. So 

 far then as the determination of iodine in the atmosphere is con- 

 cerned, the experiments were of no value. The alkalies through 

 which the air had been drawn undoubtedly contained iodine origi- 

 nally, and therefore no certain conclusion could be drawn as to the 

 probability of their being more highly iodized by contact with the 

 atmosphere. To the presence of iodine in potashes, or, to use words 

 more strictly botanical, in the ashes of forest timber, further refer- 

 ence will be made in a subsequent part of this paper. 



In the next experiment the alkalies were dispensed with, the air 

 being drawn through — 



1 . A tube with slips of starched paper, kept somewhat damp. 



2. A gas-bottle immersed in a freezing mixture ; and 



3. A gas-bottle containing a solution of nitrate of silver. 



A continuous current was kept up for fully five hours, commencing 

 at mid-day. At the conclusion of this experiment, the papers were 



