Thanks Rod - I will try and search. Curiosity killed the cat...
Apparently the original protocol is described here:
"A new method of concentrating and cleaning diatoms and other organisms" A. van der Werff
Pages 276-277 | Published online: 01 Dec 2017https://doi.org/10.1080/03680770.1950.11895297
Internationale Vereinigung für theoretische und angewandte Limnologie: Verhandlungen, 12(1), pp. 276–277 (1955)
Alternative publication name:
Societas lnternationalis Limnologiae: International Association for Theoretical and Applied Limnology
Thanks for the investigation work.
I have also seen the protocol referenced in summaries academic papers on Diatom studies. It seems it has been out there a while.
The original van Der Werff article being very short and hard to acquire, I looked in some more modern literature. There has been some research in France in 2005-2006 on mixing H2O2 with tiny amounts of dichromate (by N. Frikha and coworkers). They provide evidence that indeed, dichromate combines with H2O2 in a catalytic way: It accelerates the decomposition of H2O2 to oxygen and water, releasing considerable heat. When it is finished, dichromate remains in the mixture (this explains the yellow color of the final liquid after the dichromate reaction
). For catalysis, a tiny amount of the agent (dichromate) is sufficient, even if the amount of residual H2O2 is large by comparison.
the research indicated that the reaction rate and the rate of heating of the liquid depend on several conditions (so that, in my opinion the time to start and the intensity could vary from time to time as mentioned by rnabholz
). The reaction can get out of control (called "runaway process"). So, although the products are not toxic, it should indeed be carefully approached.
But IMHO, these results show that dichromate does not serve here as oxidizer. Neither does it amplify the oxidative power of H2O2. It does heat the mixture and create a lot of oxygen bubbles. But oxygen bubbles are not powerful oxidizer in this case. They just remove the debris mechanically. So, I agree with zzffnn, that it is equivalent to boiling and that for cleaning diatoms, warming the H2O2-diatom mixture in a water bath, even to the boiling point of the water, is safer and better controlled than the (spectacular) reaction with dichromate
Like mentioned in protocols, I think that heating the H2O2-containing mixture should be done gradually, taking precaution against splashes of hot corrosive liquid, and only when there is no strong foaming at room temperature. And I agree with photomicro that getting rid of the excess of H2O2 is not an issue, no need to employ dichromate for that.
My opinion, until other evidence is found, I would omit the dichromate from the protocol.