From: Alberto Novo (alnovo@inwind.it)
Date: 04/23/03-10:34:01 AM Z
> Well, Alberto and Katharine are proven right--yesterday I got my gum
and mixed 1+2 and 1+3 solutions. The 1+2 that Demachy and Henney and Dudley
used was volume wise exactly the same--in other words, 100g of gum mixed
into 200ml of water made a 300ml solution. Thus the 1:2 is a 33.3%
solution.
Christina, I think something did not working properly there. The final volume should have been less than the sum of weights, unless the solution were filled of air bubbles.
I say this because the gum solutions have a density (the ratio between weight and volume) higher than one; in fact, it is commonly used a 14 Baume solution. This means a density of 1.107 kg/dm3: 1000 ml of this solution weights 1.107 kg or 1 kg is in a total volume of 1000/1.107=903 ml.
Under the assumption that the 1+2 (weight/weight) solution gives a Baume density of 18 to 20 (see your first post on this argument), the corresponding density should be between 1.142 and 1.161 kg/dm3. Let us average these values to 1.15. So the concentration by weight is 33.33%, but the total volume would have been 300/1.15 = 261 ml. If so, the concentration by volume should be 30.33*1.15=38.33% (you may also calculate 100 (grams) divided by 261 (milliliters), which gives the same percentage).
Reassuming: 100 g of gum mixed into 200 ml of water should not make a 300 ml but a 250 ml solution. In any case, the final wolume has to be less then the sum of weights.
> Then 100g of gum into 300ml of water, which is the common form of
dilution nowadays it seems, is a 25% solution.
it is a a 25% WEIGHT/WEIGHT, not weight/volume
As for the preservatives, I use sodium azide, and store the solution in the refrigerator.
Alberto
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