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Scientific Proceedings (130) 



known material, the greater amount of iodin remains in the ash. 

 The alkaline solution from the absorption apparatus is evapo- 

 rated to 10 c.c. after adding to it the rinsings of the combustion 

 tube. The ash is ground with water or the solution from the 

 absorption apparatus in a ball mill and the extract is evaporated 

 to 10 c.c. The solution is acidified until P H = 1 and placed in a 

 12 c.c. separatory funnel and 0.1 c.c. of 0.1 N arsenius acid 

 added, and allowed to remain for one-half hour to reduce any 

 iodate to iodide. Then 0.1 c.c. of 5 per cent, sodium nitrite is 

 added to oxidize the iodide to iodin which is extracted with 1 c.c. 

 of CC1 4 . The partition coefficient of iodin between CC1 4 and 

 the aqueous solution is about 86, but varies with conditions. The 

 iodin in CC1 4 is run into a 1 c.c. glass stoppered bottle and cen- 

 trifuged to remove water droplets. The iodin is determined 

 colorimetrically with a Bausch and Lomb Biological colorimeter 

 specially made with cups holding 1 c.c. at 2 cm. depth, against a 

 standard solution of pure iodin in CC1 4 (1 mg. in 10 c.c). The 

 amount remaining in the aqueous solution may be calculated, 

 using an approximate partition coefficient, or it may be recovered 

 by repeated extractions. CC1 4 is freed from reducing substances 

 by oxidation with bromine in the sunlight for about a week; 

 then the excess Br is removed by shaking with a dilute solution 

 of KI and then titrating the water phase with sulphurous acid 

 while shaking the container. It is then washed and filtered 

 (and preferably dried) and distilled, rejecting the first and last 

 portions of the distillate. Standard solutions of iodin in CCI 4 

 cannot be sealed by fusing the glass without decolorizing. 

 Preserved in glass stoppered bottles it will turn yellow. The 

 color may be regenerated by shaking with 1/10 its volume of 

 water of P H =1 containing nitrous acid, but some of the iodin 

 is removed. This water may then be used to regenerate new 

 portions of standard solution without appreciable loss. 



By determining the iodin in the ash separately from that 

 caught by the absorption apparatus, the amount of CaO that 

 must be added to make the absorption apparatus unnecessary 

 may be determined, but under such conditions the combustion 

 is slow. 



By this method it was determined that bacteria remove 

 iodin from the medium. 



