Ah, the good, old pre-FDA days! I can’t imagine that “Genuine Black and White Ointment” was particularly good for you given that it proudly states that it contains 10% Mercuric Oxide. According to the Chemical Data Book, “very short exposure to small quantities may cause death or permanent injury.” I suspect you would have lots more than “freckles and other blemishes” to worry about if you used this stuff for any length of time. A quick web search shows that this product is actually still for sale though I’m pretty sure the formulation will be somewhat different in these enlightened days.
For the technically inclined...