Originally Posted by TravisRichard
Second, if SG is the weight of a (sugary)liquid in relation to the weight of pure water and if degrees Plato is the percent of sugars dissolved in a liquid by weight, then why doesn't 1.1 SG = 10 Plato?
I am not a chemist, so I could be wrong about this, but here's what I think happens. First, if I remember correctly, Plato is the weight of dissolved sugars as a fraction of the total weight of the solution, so 10 Plato would be, for example, 10 grams sugar and 90 grams water. The specific gravity, on the other hand, measures density, that is, the weight of the solution divided by its volume. When you add sugar, the volume of the solution expands to make room for the sugar molecules, so while a 10 Plato solution weighs 100/90 = 1.11 or 11 % more than the water you started with, the solution takes up more space than the original water. The SG would be 1.11 only if you could have added the sugar without the volume increasing. If the SG for a 10 Plato solution is 1.04, then the solution must have expanded to 1.11/1.04 = 1.0673, or by 6.7 %.
To put it another way, you start with 90 grams of water and add 10 grams of sugar to get a 10 Plato solution with a SG of 1.04. The solution weighs 11 % more than the water you started with, but has a volume 6.7 % greater than the original water, so the SG = 1.11/1.067 = 1.04.