[Histonet] paraformaldehyde crystals v Prills

[Carl Hobbs]

Many of our Groups use paraformaldehyde crystals ( Sigma P6148) to make up 
their solution of formalin. Works very well; 4g + 1tab PBS + 6microlitre 
10MNaOH.....stir overnight. Dissolved completely:pH7.2
I am trying to get away from using this paraformaldehyde: it is very light 
and prone to spread around the fume hood when it's weighed out.
    So, I bought PRILLS from Sigma:Problem is, they just do not dissolve 
completely, unless I preboil the water.( heating to 60C is not hot enough to 
dissolve the Prills.
 I have tried all combinations of the formulation above( eg: no NaOH, 
dissolving PBS tablet before adding paraformaldehyde).
I want the procedure with the least risk; boiling may be a higher risk than 
the spread of powder.
NB: I cannot turn down/off the fume hoods, for the weighing of the 
crystals( which behave more like a very fine powder), hence my desire to use 
the heavier Prills.

Be grateful for any insights.
Carl