Re: Stock Paint:Gum Solutions?
Dirk-Jan,
a broad definition of concentrarion is rhe amount of one substance in the
body that is containing such a substance. With the exception of molality
(not molaRity), the body is composed by the solute plus the solvent.
So 30 g of gum in 100 g of water cannot be defined a 30% solution. To be
more clear, we would refer to as a ratio like 30:100, or 30+100.
BTW, Wikipedia has a very long page about concentration.
Alberto
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 ;-)
DJ
2008/10/24 Alberto Novo <alt.list@albertonovo.it>
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.
Dirk-Jan: your 30% gum, which is for me a 23% w/w, is very close to Kees'
1+3 (if both parts are weights, it is my 25%) and the respective Baume
degrees are quite consistent.
Alberto
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