"Mark Willstatter" wrote"

This is nitpicking, I know - it doesn't sound like you were shooting
for accuracy here - but for a 10% solution you want 25 grams in 225 ml
of water, not 250.

You are apparently attempting to include the volume of the meta, and
calculating 25g / (225 ml + 25 ml) = 10 %, but 25 grams of metabisulphite
does not become 25 ml of liquid in solution!

I don't know the actual figure for meta, but sugar in solution increases the
volume by ~0.645 ml / gm, depending on temperature [Source: American
Winemaking Society], so if we were dealing with sugar, and nitpicking, the
equation would be:

25 gms sugar / 10 % - (25 gms sugar x .645 ml / gm) = 233.875 mls
water at standard temperature

I believe meta in solution increases the volume by far less than 0.5 ml / gm
(this is verified by my own rough measurements), in which case my formula is
more accurate. If it were more than .5 ml / gm, yours would be the more
accurate. If it were more than 1.4 ml / gm, neither formula would be
correct.

But there is probably more than this 1% potential error in the measuring
cups, spoons and thermometer we will be using, as well as in our ability to
fill the vessels to a precise volume.

As you said, I'm not shooting for more than +/- 10 % accuracy. If I were, I
would be determining the difference between the weight of the primary when
empty and its weight when full, and computing the volume of the must based
on its SG. Then I would add the meta by weight, not by teaspoon or graduated
syringe. And then I would still miss Mars by 10,000,000 kilometers because
of some other factor I hadn't considered.