September 8, 1922] 



SCIENCE 



269 



and its culture to open the way to that kind of 

 service which brings the joy of progress and 

 the continuing rewards of real aecomplisbnient. 

 John C. Merriam 

 Caeneqie Institution of Washington 



THE WORLD'S SUPPLY OF IODINE 

 IN RELATION TO THE PRE- 

 VENTION OF GOITRE^ 



Owing to the varying reports as to the con- 

 centration of iodine in sea water, I have made 

 a number of determinations on wat«r dipped 

 from the Santa Monica, Cal., pier. Even after 

 filtration, this water contained so much col- 

 loidal material as to interfere with the deter- 

 minations. It was finally observed that thor- 

 ough shaking with carbon tetrachloride and 

 filtration removed this sufficiently to make 

 analysis possible. The carbon tetrachloride 

 was purified by the addition of a drop of 

 bromine, action of sunlight and shaking with 

 an excess of sodium thiosulfate solution. In 

 determining this excess, some very dilute 

 sodium carbonate solution was poured into 

 the carbon tetrachloride and tenth normal 

 sodium thiosulfate run in, about half a ec. at 

 a time, followed by shaking, until the color 

 disappeared. This solution was separated ofJ 

 and more carbonate and about two cc. of thio- 

 sulfate added with thorough shaking, followed 

 by separation of the water phase. The carbon 

 tetrachloride was then dried and distilled, the 

 first distillate being rejected. 



It was found that evaporation of the sea 

 water until sodium chloride began to crystallize 

 out made it acid, due to precipitation of cal- 

 cium carbonate and the hydrolysis of MgCl,, 

 magnesium being a weak base, but there was 

 no loss of iodine. Furthermore, a dry salt 

 could be made of the sea water, without ap- 

 preciable loss of iodine. This was accom- 

 plished by evaporation until the calcium car- 

 bonate precipitated; precipitation of the re- 

 maining calcium and magnesium by the addi- 

 tion of 100 cc. of seven per cent. Na„C03 solu- 

 tion for each liter of original volume; filtra- 

 tion; washing the precipitate on the filter and 

 evaporation of the filtrates to dryness. 



1 From the Southern Branch, University of 

 California, and the University of Minnesota. 



In the analysis of the iodine content of salt, 

 it was dissolved in water and the same pro- 

 cedure followed as with brine. In analyzing 

 water or 'brine, standard solutions of the same 

 NaCl content but varying concentrations of 

 iodate were made up and treated in the same 

 way as the unknown. The quantity of re- 

 agents added varied with the samples, and no 

 portions were thrown away until the yield of 

 iodine was found to be complete. Each sample 

 if not near neutrality, was neutralized, using 

 test paper, and about 10 cc. of concentrated 

 HCl per liter added. In case buffere were 

 present, at least enough acid was added to 

 react acid to brom-phenol-blue (or methyl- 

 orange). An excess of arsenious acid was 

 added to reduce the iodate to iodide, the equiv- 

 alent of 1 to 10 cc. of tenth normal per liter, 

 and allowed to stand 20 minutes or more. At 

 this stage colloids, if present, were removed. 

 One per cent, sodium nitrite solution was 

 added to the extent of ten times the quantity 

 of arsenious acid. The sample was then ex- 

 tracted with several portions of carbon tetra- 

 chloride, which were then collected in a sep- 

 aratory funnel. In cases of 0.04 milligram 

 per 100 ec. of the sample, a pale pink color 

 could be detected in the carbon tetrachloride. 

 The smallest workable quantity, often 1 cc. 

 of very dilute (less than 0.1 per cent.) sul- 

 furous acid was shaken with the extract until 

 complete extraction of the iodine was effected. 

 The carbon tetrachloride was removed from 

 the sulfurous acid solution and a drop of con- 

 centrated sulfuric acid added, followed by 

 sufficient sodium nitrite solution to oxidize 

 the sulfurous acid and completely oxidize the 

 iodide to iodine. The iodine was extracted 

 with a sufficient quantity of carbon tetra- 

 chloride to fill the colorimetric apparatus 

 (which varied in nature with the size of the 

 jaeld) and compared with the standards. 

 There must 'be nearly the same quantity of 

 iodine in the final standard taken for compari- 

 son as in the unknown, and the treatment must 

 be identical, quantitatively, especially in re- 

 gard to volume relations and thoroughness of 

 shaking. 



The quantity of iodine found in the sea 

 water was 0.05 milligrams per liter, which is a 

 confii'mation of the findings of Winkler for 



