Parodinal crystal formation.

[el wacho]

hi all,

Does the crystal formation in the making of Parodinal indicate that the process is completed? successful?

i did a little experiment of mixing some up with a little less sodium hydroxide - 18g/250ml, which is 2g less than the original recipe calls for.
the crystals eventually formed but it took almost a day extra to form. so far the batches i've mixed up have been pretty consistent with crystal formation happening around the 72 hour mark. i'm hoping to arrive at the minimum amount of sodium hydroxide required to complete the process and am curious if the crystal formation can serve as an indicator.

thanks.

 

[Alan Johnson]

I think the crystals are at least partly sodium sulfite heptahydrate, the form in which it crystallises from water.The solubility of this is given as 266g/L:
http://www.lenntech.com/air-purification/gas-purification-techniques/solubility-in-water.htm
But even if you start off with half the amount of sodium sulfite crystals are still formed, but not so many.My guess is that these are sodium aminophenolate.
So your crystals are likely a mixture of the two.
Another guess , Rodinal does not show these crystals because of greater solubility of potassium aminophenolate.