in the English Channel near Brighton. 55 



a few drops of this ammoniacal solution of chloride of silver, 

 the solution will remain clear; but if the most minute particle 

 of an iodide be present, it will be rendered turbid. 



To the fluid under examination I added gradually, drop 

 by drop, the solution of ammonia chloride of silver, leaving 

 time between each successive addition for the precipitate of 

 iodide of silver to subside. It is well when bromides are 

 present to keep the vessel closed during the process, other- 

 wise it is of no importance. The iodide of silver collected 

 upon a small filter was first washed with a little diluted am- 

 monia, and afterwards with a few drops of diluted hydro- 

 chloric acid to dissolve any earthy substance which the pre- 

 cipitate might contain, and ultimately with pure water. 



The filter with the precipitate was dried and ignited. This 

 experiment, repeatedly performed, yielded the most satisfactory 

 results. It requires time, but this is more than balanced by 

 its accuracy. Thus, for instance, I obtained by the analysis 

 of the Congress spring of Saratoga, from 100,000 grs. of the 

 water, 0*12164 gr. of iodide of silver, representing in 1000 

 grs. of the mineral water, 0*00067 gr. of iodine. 



The ammoniacal fluid, separated from the iodide of silver, 

 was carefully evaporated to expel the ammonia, whereby a 

 small precipitate was obtained, consisting of bromide of silver, 

 which was added to that subsequently obtained. This preci- 

 pitate was formed by the solution of the chloride of silver, 

 more of which was added than was required for the separa- 

 tion of the iodine. That this minute precipitate consisted of 

 bromide of silver, was proved by heating it in a test tube with 

 concentrated sulphuric acid, whereby it became of a delicate 

 yellow colour; whereas chloride of silver would have re- 

 mained white, and iodide of silver would have obtained a 

 brown colour by parting with its iodine. 



A small portion of the fluid may now be examined for 

 bromine, and, when present, the following process may be 

 adopted, which is the same I employed for the separation of 

 bromine in sea-water and brine-springs, where the quantity of 

 chlorides is comparatively very large. The concentrated so- 

 lution freed from the iodine was introduced into a glass ball, 

 having at its lower end a glass tube, and at its upper an aper- 

 ture closed by a glass stopper. A concentrated aqueous solu- 

 tion of chlorine was added as long as any sensible yellowness 

 was caused by its addition. The fluid was then agitated with 

 pure aether; and after this had collected on the surface, carry- 

 ing with it the bromine and chlorine, the water was allowed 

 to flow off' through the tube below, and by careful manipu- 

 lation the aether could then be freed from the water, which 



