tion of free cyanide of potassium, and a large silver anode operated with a very strong electric current. The purpose

of immersion in this solution is to effect an instantaneous deposit of silver on the metal, to better insure a perfect coating in the silvering bath proper. The articles remain in the "striking" solution for a few seconds only, as its action, owing to the large proportion of free cyanide it contains, is very prompt, and as soon as they have received a thin coating, which takes place almost immediately, they are removed to the electro-plating bath, where they remain until they have received the proper coating of silver. In many cases, especially with articles of considerable size, cleansing in boiling alkali must be supplemented by “scratch-brushing," in which case the acid dip may be dispensed with, and the article, after thorough rinsing and again dipping in alkali to remove finger marks, is immersed at once in the "striking" solution.

German-silver, or nickel, articles are first cleansed in boiling alkali, washed, then dipped in a mixture of twothirds sulphuric and nitric acids, then into quicking solution, then into the "striking" solution, and from this into the plating bath.

Steel articles are cleansed in boiling alkali, rinsed, dipped in muriatic acid, then in the "striking" solution, and from this into the plating bath. In case the articles require scouring the acid dip is dispensed with. For steel two "striking" solutions are used, one somewhat richer in silver than the other, the weaker solution being used first.

In the Wm. Rogers Manufacturing Co., Hartford, Conn., one of the oldest and best establishments in the United States, the following is the general outline of the methods in use for preparing work for plating:

FOR CLEANSING STEEL (cutlery).-Immersion in boiling alkali for the removal of grease; scouring; rinsing; dipping in strong muriatic acid; then for a few seconds in a silver "striking" solution; then in the plating bath until the required amount of silver is deposited.

The formulæ for the "striking" solution, which will begiven further on, is low in silver, rich in cyanide, and worked with a strong current and a silver anode.

NICKEL-SILVER (German-silver) (for spoons).-Immersion in boiling alkali; scouring, if necessary; rinsing in water; immersion in acid mixture, composed of two-thirds sulphuric acid and one-third nitric acid; dipping in weak quicking" solution (either very dilute potassium-mercury cyanide, or acidulated nitrate of mercury); immersion for a few seconds in the silver" striking" solution; and from this into the plating bath.

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BRITANNIA-METAL (hollow-ware).-Cleansing in alkali as above; brushing; rinsing in water; again immersing in alkali to remove finger marks, if necessary; immersion in the "striking" solution, and from this into the plating solution. A "quicking" solution for Britannia, sometimes employed, is composed of a strong solution of sal-ammoniac and corrosive sublimate, into which the articles are dipped after cleansing in strong potash. The metal will plate without being scoured. The Hartford Britannia Company employs substantially the same method of procedure. Whether articles require to be scoured or not will depend, of course, upon their freedom from grease or dirt of any kind, and the operator must use his judgment as to whether he may safely dispense with it in preparing his work for plating.

The above described preparatory operations correspond in a general way with the most approved English methods, as witness the following brief statement from Gore (Elec

し

tro-Metallurgy, 162 et seq.): "Copper, brass, and German-silver are the best substances to deposit silver upon; lead is a very bad metal for the purpose, because it is so soft. Articles of iron or zinc are usually coated with a film of copper, in a cyanide solution, before putting them into the plating liquid. Those formed of Britannia-metal, tin, or pewter, are not dipped into acid before plating, but into a strong and boiling-hot solution of pure caustic potash, and are then either" scratch-brushed," or taken direct from the alkali, without rinsing in water, and immersed in a cyanide of silver solution (at about 190° F.), containing a considerable proportion of free cyanide, with a large anode, and an electric current of considerable intensity is passed through the vat for several minutes, until the articles receive a thin coating; they are then transferred to the ordinary plating solution to receive the full amount of deposit.

"Steel articles, after being cleansed in the hot potash, are dipped (without brushing) into a solution of one pound of cyanide of potassium to a gallon of water; and then coated thinly with silver in a similar manner before plating. Those of lead are first scraped or otherwise made quite clean and bright, by mechanical means, and then treated in the same manner as those of Britanniametal. Articles of copper, brass, or German-silver, after being properly cleansed, are dipped into the solution of nitrate of mercury, or a very dilute one of cyanide of mercury and potassium, then rinsed in a vessel of water, and immediately suspended in the depositing vat."

The silver" striking" solution, as used by the William Rogers Manufacturing Company, of Hartford, Conn., has the following composition, viz:—

The plating solution commonly employed by the William Rogers Manufacturing Company, of Hartford, Conn., has the following composition:—

The usual plating bath of the Meriden Britannia Com

pany has the following proportions :—

Meriden Company's Formula.

When these baths deposit their metal rapidly without the aid of electricity, it is a proof that they are too rich in cyanide, or, what amounts to the same thing, too poor in silver. A deposit effected under such conditions is rarely adherent, especially when it is made upon articles previously coppered, because then the excess of cyanide dissolves the film of deposited copper, and the silver which takes its place is easily rubbed off with the finger. This phenomenon will be particularly observed with

articles of steel, tin, lead, etc., which have been coated with copper before plating. The remedy consists in adding to the bath just so much of silver salt, that a piece of copper will not become sensibly silvered in it, without the aid of electricity.

The cold electro-silvering baths are disposed differently according to the articles to be operated upon. Those generally employed for electro-plating tablespoons and forks, etc., are contained in large, rectangular wooden troughs (Fig. 113), lined with gutta percha, or made of

Fig. 113.

wrought iron with riveted joints. They are sufficiently high to allow of about 4 inches of liquid being above the immersed objects, which should be supported equidistant from top, bottom, and sides, in which case the deposition of metal is likely to be of uniform thickness at both extremities of the objects. Each vat has a wooden