Manchester Memoirs, Vol. xli. (1897), No. 8. 17 



which gradually turns brown and then black, and an 

 immediate brown precipitate with a manganous salt. 

 With silver nitrate it gives a buff-coloured precipitate 

 similar to the one I had previously obtained from 

 Schonbein's solutions, but in this case of course it will 

 not be mixed with so much silver iodide. If nitrate 

 of silver is added to the solution containing the free acid 

 a milkiness is produced, and on boiling there is a further 

 precipitate, which contains silver iodide and iodate ; the 

 iodate can be dissolved out by ammonia. This reaction I 

 had previously noticed with the acid prepared in another 

 way. The hypoiodous acid is manifestly converted into 

 hydriodic and iodic acids : — 



3 HIO = 2HI-j-HI0 3 . 



The aqueous solution of the free acid appears to be 

 moderately stable. When it decomposes, as one would 

 anticipate, it appears to do so according to the equation 

 given above, only in this case the two acids immediately 

 decompose each other, liberating iodine.* In the case 

 of the solution made, as described, with the use of 

 aqueous solution of iodine, the appearance of free iodine 

 in the liquid is very slow ; but, by using iodine-water with 

 a little suspended precipitated iodine, a much stronger 

 solution of the hypoiodous acid is obtained, in which the 

 brown colour of iodine begins to show itself within a 

 minute or two of its being filtered. (It appears also that 

 some mercury comes through, because on standing for 

 some hours there is a slight deposit of the scarlet iodide 

 of mercury.) After standing for some time, this solution, 



* It will be somewhat difficult to measure the rate at which the 

 hypoiodous acid decomposes. Neither of the two methods mentioned in 

 the text for estimating the amount of hypoiodite is applicable when once 

 the decomposition of the acid has started, because each of them would 

 require the preliminary addition of a little alkali, and this would at once 

 -convert any liberated iodine into iodide and hypoiodite. 



