I have 1 gal each of dandelion and mango wine that are still slowly fermenting
that I want to rack this weekend. I understand that kit makers add a small
amount of potassium metabisulfite to the kit even before stabilization to
help beat off the wild yeasts and to give the must some protection from
oxidation. I'm wondering whether to add a bit at this rack and if so how
much?

From Jack's site:

Potassium metabisulfite, 1 gram = 150 ppm in 1 gallon, 30 ppm in 5 gallons
Potassium metabisulfite, 1/4 teaspoon = 225 ppm in 1 gallon, 45 ppm in 5 gallons
1 Campden tablet contains 0.55 grams potassium metabisulfite, yielding 75 ppm
SO2 to one gallon of must or wine

It would seem that it must be below 1 campden tablet so I'm thinking 1/16
of a teaspoon for about 55 ppm. I've have a set of cooking teaspoons that
are labeled dash, smidgen and something else, I can easily figure out which
is about equivilent to a 1/16th by couting the measures to fill up a 1/4 tsp.

I'm using powdered pot meta btw and perfer that to a 10% solution.

Don