It seems to me that adding another 100mL water does not give "half-strength" Part_B.
Originally Posted by Jimbob
When you add 100mL water to 100g potassium carbonate, you get about 130mL according to Sandy's instructions (The Great 21st Century Book of Pyro). So there is
100g potassium carbonate per 130mL of solution = 77g per 100mL of solution (approx)
If you add 100mL water to the 130mL which you were trying to make in the first place, you have 100g in 230mL of solution which is 43.5g per 100mL. Using 2 times the amount of this Part_B is equivalent to using a Part_B of 2x43.5=87g/100mL instead of 77g/100mL. Maybe 13% more pot.carbonate won't make much difference, but you might as well avoid the variable. You can correct it by instead of adding 100mL water, just add enough water to double the volume (130mL in this case)
(And to be really pedantic, you could mix it 1+2+99 to account for the extra water in your new Part_B.)
(Sandy's mixing instructions have caused some confusion. I think I even saw a Formulary pdf that said erroneously "add water to 100mL". Maybe it's been corrected since then.)
Is my reasoning correct?
Incidentally, here we have town water of low mineral content and I had no trouble making standard Part_B