Your question actually just got me really thinking though, and I stand by what I said in my response, as after thinking it through: weight is a measure of mass times the acceleration of gravity. Mass is a measure of the amount of matter. As matter is neither created or destroyed, and you aren't adding any matter by changing the form in which the substance exists; the mass will remain the same. The volume and density can change and if one changes the other will as well, but the mass is the same and therefor weight will remain the same.