A nickel solution for plating is at its proper working strength when it contains 11b, of nickel sulphate to the gallon of water. To maintain it at this strength attention must be paid to the anodes and their condition. As a rule. »he surface of anodes exposed to the action of the solution should exceed by one-half the surface of the goods being plated. The anodes should also freely dissolve in the solution, and therefore should not be too hard. If nickel has been drawn from the solution too fast, it will be liable to become too acid, and this condition maybe ascertained by testing it with blue litmus paper, which will quickly redden if acid is in excess. But a slight excess is permissible when plating iron and steel. An excess of acidity may be corrected by adding a small quantity of liquid ammonia; but an addition of nickel sulphate will be required also if the normal strength of the solution has been reduced. The hydrometer will show this reduction by comparing it with a sample of known correct strength. The readings on the hydrometer scale show the density of the solution, but not its temperature.

Nickel-plating solutions are always worked cold.