I've recently worked a lot with the ferrous oxides (Fe2O3, Fe3O4, FeO) dissolved in HNO3 (1M). I used the solutions to check the graphs of the Iron by spectrophotometry. Before I ran them through I added a potassium thiocyanate solution (1,5M), which makes an iron compound Fe(SCN)3 xH2O, which is a bright red. But I've noticed that after ≈4h of the spectrophotometry run, the bright red solutions turns <b>yellow</b>!
This color change was true for all iron compounds tested, but appeared the strongest in a delicious mixture of them all, from a sample of rusted steel screws.
I have been warned about the iron thiocyanates being photo degradable.
Also, the amount of water in the <b>sealed</b> flasks appeared to have decreased.
The yellow formed on the bottom of each flask and when dried had the texture of a salt.
Another observation was that when I disposed of the yellow waste, and a little yellow substance was left at the bottom, and i sealed the flasks again, there was a very dense white gas formed. I ruled out the possibility of it being NO2 or N2O4 as they are colored.
<b>Can anyone solve this very peculiar mystery?</b>