Botanical Society of Edinimrylt. 233 



t altered in the slightest degree ; the gas^-bottle (2) contained about 

 a quarter of an ounce of liquid, and the nitrate of silver (3) had not 

 been perceptibly changed. The condensed liquid was neutral to test- 

 papers ; a drop of starch was added to it, and subsequently nitrite of 

 potash and hydrochloric acid, which together form a most delicate 

 means of detecting iodine ; the result was negative. The nitrate of 

 silver solution was cautiously evaporated to one half-ounce ; sulphuret- 

 ted hydrogen added to precipitate the silver, and liberate as hydriodic 

 acid any iodine which might be present ; the liquid raised in tempe- 

 rature, carefully avoiding ebullition, and filtered. The filtrate, on 

 the addition of starch, nitrite of potash and hydrochloric acid, did 

 not exhibit the slightest trace of iodine. Mr. Macadam therefore 

 concluded, that in the large volume of air which he had drawn through 

 the arrangement, there had not been an appreciable amount of iodine. 



The experiments as yet referred to were made at different heights 

 on Arthur's Seat, and their negative results led to arrangements being 

 made for a trial on a scale much more extensive. Through the kind- 

 ness of the proprietor of Kinneil Iron Works, the author was enabled 

 to proceed to I3orrowstowness, and attach his apparatus to the re- 

 ceiver from which the air under great pressure is forced into the 

 blast-furnaces. By means of a stop-cock fixed in the receiver and a 

 long flexible tube, the air was conducted to the following arrange- 

 ment : — 



1. A wide tube containing slips of paper dipped in starch. 



2. A condensing worm, surrounded by a freezing mixture and 

 attached to a receiver. 



3. A tall jar containing chips of pumice-stone and a few iron filings, 

 with sufficient water to cover them. 



4. A similar jar with pumice-stone, scrapings of clean lead and a 

 solution of acetate of lead. 



.5. A condensing worm immersed in a freezing mixture and attached 

 to a receiver. 



The air, under a pressure of 3 lbs. on the square inch, was allowed 

 to traverse the arrangement for fully four hours, when the apparatus 

 was taken asunder, and the contents of the vessels being placed in 

 stoppered bottles, the whole was brought to Edinburgh for examina- 

 tion. The slips of paper (1) were not sensibly altered in tint, and 

 did not betray the slightest indications of even a rose colour when 

 moistened with distilled water. The condensers (2 and .5) contained 

 each a very small quantity of liquid, which, on being tested, did not 

 shov/ a trace of iodine. The small quantity of liquid in the con- 

 densers may be accounted for by the comparatively high temperature 

 possessed by the air rushing through so quickly as it did. The con- 

 tents of the jar (3) were thrown on a filter, and washed with cold 

 water. To the filtrate was added half an ounce of a solution of car- 

 bonate of potash, and the whole evaporated to a quarter of an ounce ; 

 no iodine was present. The carbonate of potash used in this trial 

 was prepared by calcining cream of tartar, and was so far free from 

 iodine, that none could be detected in 2 oz. of the solution, of which 

 half an ounce was employed. There was therefore no likelihood of 

 iodine being added in the alkali used, even though the analysis of the 



