Mr. Waterton's Method.
Put a good large teaspoonful of well-pounded corrosive sublimate into a wine bottle full of alcohol (spirits of wine). Let it stand over night, and the next morning draw it off into a clean bottle. When the solution is applied to black substances, and little white particles are perceived on them, it will be necessary to make it weaker, by the addition of some alcohol.
A black feather dipped in the solution, and then dried, will be a good test of the state of the solution; if it be too strong it will leave a whiteness upon the feather.