6 Tam.OR, Reaction of Iodine zvitJi Mercuric Oxide. 



present in the filtrate as compared with the iodine present 

 as h)'poiodite, and the amount is so small that, even if all 

 of it existed in the filtrate as h)-poiodite of mercury, it 

 would only account for one-third of the total iodine. We 

 may therefore conclude that at least two-thirds of the 

 iodine exists in the filtrate as hypoiodous acid. 



The filtrate, when it has been allowed to stand for a 

 considerable time, so as to become completely decom- 

 posed, illustrates remarkably well the fact, which was 

 first pointed out by Mylius {Ber. Dent. Clitin. Ges., Bd. 

 XX., p. 688) that iodine, in complete absence of hydriodic 

 acid or a soluble iodide, gives no blue compound with 

 starch. According" to Mylius, the blue iodide of starch 

 always contains hydriodic acid. The filtrate referred to 

 contains free iodic acid, which would immediately 

 decompose an\- hydriodic acid or soluble iodide, so that 

 the liquid is quite free from either of those bodies ; 

 consequently, although containing free iodine, it gives no 

 blue colour with starch. The addition of almost any salt 

 of the alkalies will at once produce the well-known blue 

 compound. 



One can only surmise as to what course the decom- 

 position of the hypoiodous acid solution follows when 

 allowed to stand. In all probability some of it simply 

 decomposes into hydriodic and iodic acids : — 

 3HIO=2HI + HICI, 



Of course these two acids would immediately decom- 

 pose each other (see above), with liberation of iodine, and 

 the hydriodic acid would also decompose part of the 

 remaining hypoiodous acid. When complete decom- 

 position has taken place, the filtrate consists practically 

 of a solution of free iodine and iodic acid. 



Central School, 



Manchester. 



