pantone159 - 13-9-2006 at 11:11
Is there a favored form of persulfate compounds (e.g. cheapest/best keeping/most pure/etc).
Ammonium persulfate is more soluble than potassium persulfate, I couldn't find data for sodium persulfate. There is also something called "Oxone",
which is something like 2 KHSO5 / KHSO4 / K2SO4.
Since the peroxodisulfate ("persulfate") splits up in water (IIRC) I'm guessing than "Oxone" is more or less equivalent to real persulfate.
woelen - 13-9-2006 at 13:35
Persulfate, S2O8(2-) does not split up in water. No peroxide is formed (e.g. no blue color is produced with acidified dichromate, while this is a VERY
sensitive test for peroxide).
I have (NH4)2S2O8 and this stores indefinitely, provided it is stored absolutely dry and in a very well closed container. I also have Na2S2O8. This is
less hygroscopic than the ammonium salt, but it is said that this slowly decomposes on standing, giving off O2. In the long run, sodium persulfate is
not stable. Potassium persulfate is the most stable on storage, but it has only moderate solubility. I have all three of them, and for experiments I
like the sodium salt the most (only persulfate is the active ion), then ammonium persulfate (which dissolves very well) and last potassium persulfate,
which is not sufficiently soluble to my opinion.
As pyro-oxidizers, all these persulfates suck. I have tried making some mix with these, but these peroxides have a too low free oxygen level, compared
to their weight. Only one of the oxygens of the entire S2O8(2-) ion is available for oxidation purposes.
chemoleo - 13-9-2006 at 13:38
Actually, sodium persulphate and sulphur does burn... very slowly! Good stuff for fuses, who knows. Plus lets not forget the complex persulphates,
i.e. copper amine persulphate, which DO burn rather well 
Otherwise I agree, the sodium persulphate is best for most purposes, and easily obtained.