Silver Acid?

It's probably much the same stuff as mentioned in this thread - Schwerter's solution, a mixture of nitric acid and dichromate salts. Not the sort of stuff you really want to be exposing your coins to.

On the coin in question: just because it tests silver, doesn't mean it's a genuine coin. The Chinese fakers have been known to buy up scrap "bullion silver" and use it to make quality fake coins from "proper" silver. A genuine Kirin dollar like that (KM/Y#183a, cyclical date 1900 AD, looks about EF condition) catalogues at $350 - easy money for a skilled faker.

Thanks for the replies. I had no doubt that the coin was a fake, but the seller claims the silver acid proved the coin to be 92.5% silver. I thought that sounded a little too precise for something akin to a litmus test.