1898 - 99 .] Dr Hugh Marshall on Per sulphates on Iodine. 389 
was not further investigated at the time; it was assumed to be 
iodic acid. 
Some months ago, my attention was again called to the subject 
by seeing an abstract of a paper on the determination of 
chlorine, bromine, and iodine in organic compounds by distilling 
the substance with a mixture of sulphuric acid and persulphate. 
The possible oxidation of iodine under these conditions was 
apparently overlooked, and the method may therefore not be so 
accurate for that substance as in the case of chlorine or bromine ; it 
was therefore important to have the nature of the action definitely 
settled by isolating some of the product. For this purpose, four 
or five grams of iodine were digested in an Erlenmeyer flask with 
a strong solution of ammonium persulphate, the quantity taken 
being more than sufficient to convert the iodine into periodate. 
The loosely-corked flask was placed on an ordinary heating coil, 
so that its temperature varied from 10°-15° during the night to 
30°-35° during the day. In the course of fully a week the whole 
of the iodine had dissolved and oxidised, and in its place there was a 
moderate quantity of a white crystalline solid. This was filtered 
off, washed with a little cold water, and recrystallised from 
solution in hot water. Its solution was strongly acid, free from 
sulphate, and gave all the ordinary reactions of an iodate and of 
an ammonium salt ; it was evidently ammonium hydrogen iodate. 
The original mother liquor and washings, containing chiefly 
ammonium hydrogen sulphate, were neutralised with ammonia 
solution, whereupon a considerable quantity of white crystalline 
precipitate formed, probably normal ammonium iodate. In order 
to prove conclusively that it was iodate and not periodate, its 
oxidising power was determined by means of potassium iodide and 
sulphuric acid, the liberated iodine being titrated with an empirical 
solution of sodium thiosulphate. The titre of the latter was found 
by comparison with pure ammonium iodate prepared by other 
methods. It was thus found that 0T540 grams of substance 
corresponded to a volume of thiosulphate solution equivalent to 
0T534 grams of ammonium iodate. There is therefore no doubt 
that persulphate oxidises iodine to iodic acid. 
Since the above investigation was carried out there has appeared 
a paper on the action of potassium persulphate on potassium iodide, 
