Well, as noted, all those old disinfectants were different. When “bright purple” was mentioned, for me, it didn’t recall mercurochrome (bright red, not very stinging) or merthiolate (darker red, somewhat stinging) or iodine (brown, very stinging); instead, it recalled gentian violet solution (bright violet, no stinging, used by physicians then). I don’t usually use anything for small nicks of my skin, but there are a lot of antibiotic Neosporin-type things around these days.
As to mercury poisoning, I’m no expert on that, but I believe that’s from mercuric salts, and if metallic mercury or complex organic compounds of mercury have no chance to get into a mercuric salt, there shouldn’t be a problem. It’s not the amount; it’s the form.
Ray