To any desired quantity of chloride of silver in water add, little by little, cyanide of potassium, shaking well at each addition, until all the cyanide is dissolved. Continue this operation, and add the cyanide, until all the precipitate is taken up and held in solution.
This solution is now ready for the plate-cup. Enough water may be added to cover any sized plate when held perpendicular in the cup. The strength of the solution may be kept up by occasionally adding the chloride of silver and cyanide of potassium. There should alway be a very little excess of the cyanide.