14 Analysis of Sea Water. 



The iodide of starch will likewise keep unchanged much longer 

 in a solution of chlorides exposed to light and air than in pure 

 water. 



The bromides when present in large quantity interfere with 

 the delicate reaction upon traces of iodine, but when the quan- 

 tity of iodine is not too small the reaction is very distinct, as a 

 small proportion of free bromine will, like chlorine, decompose 

 the iodide, and produce the characteristic reaction. 



After these experiments I tested fresh sea-water for iodine in 

 the manner before described, but did not obtain the slightest in- 

 dication of it. I now added one millionth part of the iodide of 

 potassium, and the color produced by the test did not differ in 

 the slightest degree from a solution of chlorides of the same spe- 

 cific gravity as sea-water, treated in the same manner, and from 

 this I immediately inferred, that iodine, if present in sea-water, 

 must be so in very minute quantity. 



I took 73 pounds troy of sea-water, and boiled with a quan- 

 tity of caustic potash, sufficient to precipitate the alkaline earth, 

 and after filtration evaporated ihe fluid to four ounces. On test- 

 ing a small quantity of this concentrated water, no iodine was to 

 be detected, and it was found on adding a minute quantity of an 

 iodide that the presence of bromides in comparatively large quan- 

 tity interfered with the test. But although these results appear- 

 ed to negative the presence of iodine, I felt convinced it must 

 exist in sea-water, being present in so many sea plants and 

 animals. 



Sarphate, in his " Commentatio de lodio,^^ 1835, Leiden (a 

 treatise which received the prize), states that he could detect no 

 iodine in the sea-water near the Dutch coast. Professor Charles 

 Daubeny likewise mentions, in his " Memoir on the occurrence 

 of iodine and bromine in certain mineral waters of South Brit- 

 ain, 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 care- 

 fully neutralized the solution with hydrochloric acid. The re- 

 siduum was then evaporated to dryness, ignited, and treated with 

 anhydrous alcohol. The alcoholic fluid was afterwards evapo- 

 rated, and the dry residue dissolved in a few drams of water, 



