Re: Stock Paint:Gum Solutions?
I'm a chemist, too.... And there's a difference in definition i guess, that is confusing the concentration of gum solutions.
When making a 30% solution, you weigh 30 grams, and dissolve this into 100 grams of solvent (water, in the case of gum).
The final solution, however, is not a solution with a concentration of 30% w/w gum. You indeed are are correct that my 30% solution in fact has a 23% concentration of gum in water. So, the concentration of gum in water (w/w) is 23%. The solution itself, though, remains a 30% gum solution (and indeed, this does not reflect the concentration but the 'recipe' for making the solution)...
just to make things easier for the non-chemistry people around here ;-)
2008/10/24 Alberto Novo <email@example.com>
This discussion about baume, concentration etc. periodically returns on the list. I myself have had some difficulties the first time I started printing gum, because very often the concentration is expressed in a fake percentage, like 30% for a mix made from 30 g of gum plus 100 mL of water. For me, as a chemist, this was very puzzling because this is not 30% but 30/(30+100)= 23% weight/weight. Also very confusing is parts/parts, because the units of such parts are not declared. Is it weight/weight, or volume/volume? In the first case, 1+3 leads to 25% w/w, and 1+2 leads to 33% w/w.