Thank you for the three  replies. Much appreciated. My apologies for any 
confusion caused:
I regularly use a Formalin fixing solution derived from the concentrated 
Formalin solution. I also need to  use a Formalin fixing solution derived 
from Paraformaldehyde for certain immunostaining instances. I do make up the 
latter in bulk and freeze in the small aliquots required for T/C cell 
monolayer fixing.
 I don't have any problem making up either of the solutions.
The latter dissolves completely.
What I really want to do is to use Prills instead of paraformaldehyde 
crystals. Unfortunately, they do not completely dissolve - around 80% 
disssolved after 24hrs. Sure , I can filter afterwards, but, I want to 
establish the SOP with the least risk/handling . Hence my request for help. 
Does anyone have any experience of using Prills?
Thanks for the "Fischer" suggestion....I will check them out over here.
Best wishes
carl 


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