IODINE CONTENT OF SEA FOODS 7 



rate the bulk of the water-soluble inorganic salts from the iodides, 

 the evaporated water extract was extracted with hot 95 per cent 

 alcohol. The cake was rubbed to pieces with a stu-ring rod and the 

 alcohol decanted through a filter. The alcohol extraction was 

 repeated until the total volume of the filtrate was about 50 cubic 

 centimeters. 



This solution was then evaporated to dryness and the residue 

 taken up in a little water. The resultant solution should be colorless; 

 if it was dark it was transferred to a platinum dish and again evapo- 

 rated to dryness and again ignited until the residue became light in 

 color, after which it was taken up in water and filtered through a 

 small filter into a 60-cubic centimeter beaker. 



The solution was then made shghtly acid to litmus with iodine-free 

 hydrochloric acid, and a small crystal of calcspar added. After 

 diluting to about 15 cubic centimeters, 1 cubic centimeter of freshly 

 prepared chlorine water was added and the solution boiled rapidly 

 until its volume had diminished to 2 to 3 cubic centimeters. After 

 cooling, a small crystal of pure potassium iodide was added and a 

 drop of starch solution. Thousandth-normal sodium thiosulphate 

 was then added from a burette until the blue color disappeared. 

 The quantity of iodine in the original sample can be calculated from 

 the following equations^ 



HI03 + 5HI = 3l2 + 3H20 



31, + GNaoSA = 6NaI + 3Na2S,Oe 



Upon the addition of the chlorine water to the acid solution any 

 iodine in the form of iodide is immediately set free. The boiUng 

 with the excess of chlorine oxidizes the iodine to iodic acid, and also 

 volatihzes the surplus chlorine. Upon the addition of potassium 

 iodide to the cool acid solution the iodic acid immediately oxidizes 

 five molecules of hydriodic acid to iodine. Each six molecules of 

 thiosulphate required in the final titration indicates the presence of 

 one atom of iodine in the original sample. 



Great care was taken to make sure that all chemicals used in the 

 analyses were iodine-free. The alcohol and hydrochloric acid were 

 always purified to remove traces of iodides. 



By this method amounts of iodine as small as one-milUonth of 1 

 per cent could be estimated. 



The results of the analyses are presented in the following table. 

 Except where noted, the determinations were made on the edible 

 portion of the muscle parts of the fresh fish. The results have been 

 calculated on both the fresh and the water-free basis. 



