V 



IX.] CHEMISTRY OF NATURAL WATERS. 143 



ocean, as is well known, contain but traces of iodine,* and in 

 some strongly saline springs of the first class, like that of 

 Whitby, it is only in the alcoholic extract of the salts from 

 this water that iodine can be detected. The Hallo well water 

 ( 36), which closely resembles this in its general composition, 

 and in the proportion of bromides, is, however, so rich in 

 iodine that its presence can readily be discovered without pre- 

 vious evaporation. It is sufficient to add to the recent water 

 acidulated by hydrochloric acid a little solution of starch and 

 a few drops of nitrite of potash, to produce an intense blue 

 color. The iodide of sodium in the first-named water was 

 found equal to 0.0017 parts of the solid matters, and that of 

 the second to 0.019, or nearly twelve times as much. The 

 uncoiicentrated saline waters from the two springs of Ste. Gen- 

 evieve, which belong to the second class, also give a strong 

 reaction for iodine, and when acidulated with hydrochloric 

 acid, without previous evaporation, yield with a salt of palla- ^ f 

 dium a precipitate of iodide of palladium after a few hours. 

 The salts from these two springs of Ste. Genevieve, though 

 poorer in bromides, are much richer in iodides, than the waters 

 of Hallo well; one of the former containing in 100 parts of 

 salts no less than 0.138 of iodine, so that there appears to be 

 no constant proportion between the chlorides, bromides and 

 iodides of these saline waters. 



60. The relations of bromides and iodides to argillaceous 

 sediments have yet to be determined. It would appear from 

 the facts just cited that bromine has in the course of ages been 

 slowly eliminated from insoluble combinations, and, like potas- 

 sium, has accumulated in the waters of the ocean ; while the 

 facts in the history of iodine seem to point to a process the 

 reverse of this, in other words, to a gradual elimination of 

 iodine from the sea- waters, and its fixation in the earth's crust. 

 The observations of numerous chemists unite to show the fre- 

 quent occurrence of small portions of iodine in some unknown 

 combination, in sedimentary rocks of various kinds ; from which 



* [See in this connection the late researches of Sonstadt, noticed at the 

 end of Essay XII.] 



