Manchester Memoirs, Vol. xli. (1897), No. 8. 15 



with mercuric oxide," filtered, neutralised with potash, 

 and added magnesium sulphate, so obtaining a white pre- 

 cipitate. The addition now of a few drops of potassium 

 iodide stained the precipitate brown. This certainly pointed 

 to the presence of a hypoiodite, which would be decom- 

 posed, with liberation of iodine, by potassium iodide. I 

 thought the reaction might possibly be due to iodic acid, 

 which is usually said to be the sole product of the action 

 of iodine on mercuric oxide ; but experiment convinced 

 me that it was not. Further investigation soon showed 

 that hypoiodous acid is really produced when iodine water 

 is shaken up with mercuric oxide (the precipitated oxide 

 is far the best) and filtered. Many others besides Walker 

 and Kay have no doubt prepared the acid in this way but 

 failed to recognise it. The explanation is that the 

 bleaching action of the free acid is excessively feeble as 

 compared with Schonbein's solutions. Contact with the 

 indigo solution for a long time causes the colour slowly to 

 disappear, but the addition of a drop of alkali immediately 

 transforms the acid into as strong a bleaching solution as 

 Schonbein's solutions. 



I may at once state what appears to me a possible 

 explanation of what seems at first sight a most extra- 

 ordinary anomaly — that a free acid has a very much 

 feebler oxidising power than one of its salts ! When 

 hypoiodous acid bleaches, I suppose it does so according 

 to^the following equation: — 



HOI=HI+0. 



It thus produces hydriodic acid, an extremely unstable 

 body itself, and, further, a compound which would 

 immediately decompose the remaining hypoiodous acid. 

 On the other hand, in presence of an alkali, the result of 

 losing oxygen would be to produce sodium or potassium 

 iodide, both perfectly stable bodies, and with any ten- 



D 



