This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
I have seen great relief given, even in obstinate forms of these maladies, by lotions containing hydrocyanic acid in sufficient strength. Pereira states that he did not observe relief in such cases, but he seems to have used only 2 dr. of acid in 1/2 pint of water. I have recommended 1/2 oz. or more in 10 oz. of liquid (rose water), and have never seen ill effects, but such a remedy should not be placed in careless hands, nor ordered if the skin be excoriated; sometimes a much smaller proportion will answer well, and especially when mixed with lead or soda lotion. The cyanide of potassium has also been used for lotion and ointment in the strength of 1/2 dr. to 8 oz. of liquid, or 1 oz. of cerate; a greater strength has caused severe irritation.