54 Dr. G. Schweitzer's Analjjsis of Sea-water as it exists 



Charles Daubeney likewise mentions, in his " Memoir on the 

 occurrence of iodine and bromine in certain mineral waters 

 of South Britain, May 1838," that he could not detect iodine 

 in the residuum of sea-water taken from the English Channel 

 near Cowes, after having reduced ten gallons to less than half 

 an ounce. 



To proceed with my experiment, I freed three ounces as 

 much as possible from the chlorides by crystallization, having 

 first carefully neutralized the solution with hydrochloric acid. 

 The residuum was then evaporated to dryness, ignited, and 

 treated with anhydrous alcohol. The alcoholic fluid was af- 

 terwards evaporated, and the dry residue dissolved in a few 

 drams of water, when the before-mentioned test readily in^ 

 dicated a slight trace of iodine. 



With respect to the quantity of iodine in sea-water, it is 

 evidently very minute, IT^ pounds troy not containing one 

 grain. This is remarkable when we consider the compara- 

 tively large quantity of iodine and bromine present in sea 

 plants and animals, hence we must conclude that these prin- 

 ciples are concentrated by vital action. 



Bromine when present in fluids is easily detected by chlo- 

 rine, which produces a yellow colour. If present in very 

 minute quantity the fluid must first be concentrated. But 

 when iodine is present we cannot apply this test, as bromides 

 and iodides are both decomposed by it ; and we cannot se- 

 parate them, even by means of aether, as iodine is soluble in 

 that menstruum, and also possesses greater colouring pro- 

 perties than bromine. From these causes this test is useless 

 when iodine is present, and is only certain when we are pre- 

 viously assured of the absence of that substance. 



The following process for the separation of iodine, chlorine, 

 and bromine in fluids containing these substances in very 

 small quantities has given me satisfactory results, as I had 

 anticipated by previous experiment. 'I'he fluid while boiling 

 was mixed with a sufficient proportion of caustic potash ; my 

 object in this was to decompose the earthy salts, and at the 

 same time prevent the iodine and bromine from being dissipated 

 by heat. The filtered fluid was then evaporated to dryness 

 and ignited, and the resulting mass, after having been dis- 

 solved, concentrated, and neutralized with hydrochloric acid, 

 was carefully mixed drop by drop with an ammoniacal solution 

 of chloride of silver prepared by mixing one part of a satu- 

 rated solution of recently precipitated chloride of silver in 

 ammonia with one of liquid ammonia (sp. grav. 0'035) and 

 two parts of water. If to a concentrated solution of chloride 

 of sodium containing one thirtieth part of a bromide, we add 



