Given you are rubbing bits off left right and centre, why not take it to a bullion dealer and cash it in? There won't be much left soon.
You can always do a specific gravity check. Alternatively, 17mm diameter, density of gold is 19.32g/cm3, density of copper is 8.96g/cm3 assuming it isn't alloyed with silver in which case use 10.49g/cm3, weight 1.6129g for the complete thing without hole, reduce the weight by about 7% for the hole, purity if it was gold would be 0.9000, volume of a cylinder is 3.14 x 0.852 x height. You can therefore work out if it is gold just by establishing the thickness, give or take a bit seeing as it isn't a flat disc.
19th century gold coins were not made from white gold. This is something driven by modern fashion tastes. It would be bog standard gold alloyed with bog standard copper or bog standard silver on a 9:1 ratio.