Manchester Memoirs, Vol. xli. (1897), No. 8. 5 



then, in another experiment, with the same solution of 

 iodine, the bleaching action, without any apparent reason, 

 ran up to 30 or even 40% above the theoretical amount, that 

 is above the amount which it ought to be if the whole of 

 the iodine used had been converted into iodide and hypo- 

 iodite according to the equation 



2 KOH+I 2 ==KI+KOI-{-H 2 0. 



Similar anomalous results were obtained when solutions 

 of bleaching powder or of sodium hypochlorite were used 

 instead of chlorine water. These extraordinary results 

 were ultimately found to be due to a very strange action 

 on the part of the indigo, an action of which I can at 

 present offer no explanation. The excess of bleaching 

 action upon the indigo is not permanent ; on standing for 

 a minute or two the blue colour returns. This of course 

 is not the case with what I may call the genuine bleach- 

 ing action. If one cubic centimetre of indigo solution in 

 excess of what is permanently bleached be added, although 

 there appears to be no indication of when the end-point 

 is being passed, on standing for a minute or two a blue 

 colour appears. I further found that this curious tempo- 

 rary bleaching action only occurs when a large excess of 

 alkali (in comparison with the amount of iodine present) 

 has been used. 



Now, of course, it was possible to determine the 

 amount of permanent bleaching action. The following 

 example is one out of a great many experiments which 

 I made : — 



20C.C. of the aqueous iodine solution (='0035 iodine),, 

 after the addition of alkali bleached 15 c.c. of standard 

 indigo solution, 1 c.c. of which (titrated with standard 

 solution of chlorine) corresponded to '000228 of iodine, 

 so that the amount of iodine indicated by the bleaching 

 action was '000228 Xi5='00342, which was practically the 



