U of S | Mailing List Archive | alt-photo-process-l | Re: Stock Paint:Gum Solutions?

Re: Stock Paint:Gum Solutions?

I always assumed that 1+2 is w/w since gum can be in various forms;
powder, tears and lumps, therefore the only logical conclusion is that
it's expressed in w/w (or w/v, since density of water is 1 g/ml, therefore
weight and volume are interchangeable - keeping the scale proportional).
Someone is perhaps still using volume tools, like cups. In addition, one century ago this was more usual than weighting, so I ever look at those parts with suspicion.
When expriming concentration, you have to consider also the volume of the solute in the final total volume or keep into account the resulting density. So, using the densities measured by Kees:
1+3 = 25% w/w = 25*1.101 = 27.5 w/v
1+2 = 33.3% w/w = 33.3*1.132 37.7% w/w
One among the best example is concentrated sulphuric acid. It is sold as 98% w/w, with a density of 1.84 kg/dm2. This means 98*1.84 = 180% w/v.
This seems absurd, but it simply means that in 100 mL of conc. sulphuric acid there are 180 grams of pure substance.