sulphate by the addition of bicarbonate of sodium, filters and dissolves the well-washed precipitate in acetic acid, with the aid of heat.

The acetate of calcium he prepares by treating caustic lime, or the carbonate (marble-dust) with sufficient acetic acid to dissolve it with the aid of heat. The solution of these salts is acidified, slightly but distinctly, with acetic acid.

This solution, which we have worked with under a variety of circumstances, we have found to be in many respects an excellent one. It gives satisfactory results, without that care and nicety in respect to the condition of the solution and the regulation of the current which are necessary with the double sulphate solution. The metallic strength of the solution is fully maintained, without requiring the addition of fresh salt, the only point to be observed being the necessity of adding, from time to time (say once a week), a sufficient quantity of acetic acid to give a distinctly acid reaction. The Potts solution is rather more sensitive to the presence of a large quantity of free acid than to the opposite condition; as the former condition is apt to produce a black deposit, while it may be run down nearly to neutrality without notably affecting the character of the work. The deposited metal is characteristically bright on bright surfaces, and requiring but little buffing to finish. It does not appear, however, to be as well adapted for obtaining deposits of extra thickness, as the commonly used double sulphate of nickel and ammonium. On the other hand, its stability in use, the variety of conditions under which it will work satisfactorily, and the trifling care and attention it calls for, make it a serviceable solution for nickeling.*

* From experiments of the writer, there would seem to be grounds for the belief that a double acetate of nickel and calcium is formed in the

FORMULE FOR NICKEL-PLATING SOLUTIONS.

No. 1.

Double sulphate of nickel and ammonium 5 to 8 parts.

Water

100 66

Dissolve the nickel double salt in the above quantity of water with the aid of heat. Cautiously add ammonia, or the sulphate of ammonium, until the solution is neutral to test-paper. This solution should be maintained as nearly neutral as possible in use. This is commonly known in the United States as the Adams solution. It is in very general use by nickel-platers throughout the United States, and yields, when properly managed, excellent results.

(Weston's solution.) The superiority of this solution is generally acknowledged. The deposited metal, as previously remarked, is almost silver-white, dense, homogeneous and tenacious; and the solution maintains its excellent working quality very uniformly in long-continued service.

The nickel salt and boric acid may be dissolved separately in boiling water, the solutions mixed, and the volume brought up to that of the formula, or the two components may be dissolved together.

Potts solution. As prepared according to the formula given by the inventor, however, it contains a considerable excess of the acetate of calcium beyond that required for the formation of a double salt, the presence of which renders the determination of the fact very difficult.

To each gallon of this solution add 1 fluidounce acetic

acid 1.047 sp. gr.

To prepare this bath, dissolve about the same quantity of the dry carbonate of nickel as that called for in the formula (or three-quarters of that quantity of the hydrated oxide) in acetic acid, adding the acid cautiously, and heating until effervescence has ceased, and solution is complete. The acetate of calcium may be made by dissolving the same weight of carbonate of calcium (marble-dust) as that called for in the formula (or one-half that quantity of caustic lime), and treating it in the same manner. Add the two solutions together, dilute the volume to the required amount by the addition of water, and then to each gallon of the solution add a fluidounce of free acetic acid, as prescribed. (Potts's solution.)

The solution is made with the aid of heat, and when cool, small fragments of carbonate of ammonium should be added until the bath is neutral to test-paper.

(Powell's solutions.) These solutions yield good results, but their complex composition must debar them from general use.

This bath is similar to that recommended by Prof. Boettger; it is said to be well suited for the purposes of amateurs, inasmuch as it gives good results with a platinum anode. It is worked at a temperature of 100° Fah. with a moderate current. It requires renewal from time to time as it becomes impoverished in nickel, by addition of fresh nickel salt; it must also be kept alkaline by the occasional addition of ammonia.

Dissolve in boiling water and allow to cool. These proportions are recommended for coating objects of cast and wrought iron, and steel.

When solution is complete, dilute with twenty or thirty times its volume of a saturated aqueous solution of bisulphite of sodium. (Roseleur.)

This is the solution employed by Roseleur (see ante). The deposit has a dull, gray color.

Watt (Electro-Metallurgy, 7th ed., p. 94) recommends for ordinary purposes the following solution, which he affirms will give, in careful hands, very good results. "Take, say 2 ounces of pure nickel, dissolve in hydrochloric acid, taking care not to have an excess. A gentle heat will assist the operation. When dissolved, dilute the solution with 1 quart of cold water. Now add ammonia gradually, until the solution is quite neutral to testpaper. Next, dissolve 1 ounce of sal-ammoniac (chloride of ammonium) in water, and mix this with the former solution. Lastly, evaporate and crystallize slowly." The resulting salt will be the double chloride of nickel and ammonium. It is one of the earliest solutions used for