General Distribution of Iodine. oil 



iodine. In my last experiment, where I subjected to examination 

 100,000 cubic feet, or 625,000 gallons, I ought at the same rate to 

 have obtained several ounces of a liquid, every drop of which should 

 have attested the presence of iodine. gfi t 



At the intervals which elapsed between the trial of these experi- 

 ments, I was examining large portions of the rain Mater which fell 

 in Edinburgh during this summer. I was careful not to employ the 

 alkalies in any shape, although I was led to infer from Chatin's 

 papers that potassa had been used by him* In the first experiment 

 I added to three gallons of the water some ounces of a solution of ace • 

 tate of lead. On standing twenty-four hours, a precipitate had fallen 

 to the bottom, from which the liquid was drawn off. The precipitate 

 was treated, as described in a former part of this paper, and no iodine 

 was detected. As the iodide of lead is slightly soluble in wat'-r, and 

 might have been present in the liquid which had been removed from 

 the precipitate, this liquid was evaporated to one ounce, and after- 

 wards tested for iodine, but none was found. A second experiment 

 was tried with a similar volume of rain water, viz., three gallons, 

 substituting nitrate of silver for acetate of lead ; a precipitate was 

 observed after standing twenty-four hours, but neither it nor the 

 liquid contained a trace of iodine. To a third quantity of twelve 

 gallons, I added acetate of lead, and without separating the preci- 

 pitate from the liquid, the whole was evaporated down to one ounce, 

 and tested for iodine, but without giving a positive result. An- 

 other experiment made with three gallons of rain water, which had 

 been collected at Unst, in the Shetlands, and to which acetate of 

 lead was added, gave also a negative result. 



The proximity of Edinburgh to the sea, the direction of the pre- 

 vailing winds, and the falling of the rain used in these researches 

 after somewhat lengthy droughts, all tended to make the rain water 

 of the district in a condition highly favourable for the object in view. 

 This remark applies with special force to the water received from 

 Unst which had fallen in the immediate vicinity of the ocean. Cha- 

 tin announces that the proportion of iodine in rain water is very 

 variable. At one time 10 litres of water collected at Paris, gave 

 one- fifth of a milligramme, and at another time, the same quantity of 

 water produced half a milligramme. Did all rain water contain as 

 much as the least of these quantities, then a very distinct coloration 

 would be exhibited by one gallon evaporated to a quarter of an ounce. 

 In my researches just detailed, three and even twelve gallons were 

 found insufficient to give the faintest indication. 



So far, then, as my investigations on the presence of iodine in the 

 atmosphere and in rain water are concerned, I am forced to believe 

 that at the time I experimented, there was not a sufficient quantity of 

 this element present in either, to respond to the delicate test I era- 



* Comptes Rcndup ; tome xxxi., p. 282. 



