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Decomposing Cell

This is a vessel of suitable shape and dimensions, con- cell (see No. 3334), and is the receptacle or taining the plating or electrotyping solution; vessel in which the process of electroplating and is usually furnished with appliances over is effected. The above description will give it for suspending and sustaining in their pro- a tolerably clcar idea of the principles of a per position the negative electrodes or arti- simple galvanic battery. Different kinds of cles to receive the metallic coating, and their batteries are only different modifications or corresponding positive electrodes, or plates of applications of the same principles, and have metal, which serve to complete the electric each their special excellence; but for electrocircuit, and whose decomposition serves to plating, Smec's battery is the one usually keep up the strength of the solution. The positive electrode must always be of the same metal as that which the solution contains. adopted. 3666. To Construct a Cheap Galvanic Battery. Take a gallon stone jar, and place a sheet-zinc cylinder therein, and inside that a porous cup (a porous flower-pot with a cork fitted in the hole will answer a picce of sheet copper. Use a solution of

3665. The Principles of the Galvanic Battery Explained. If a piece of ordinary metallic zinc be put into dilute sulphuric acid, it is speedily acted upon by the acid, and after a fashion). Inside the porous cup place and a little mercury be rubbed over its surface, an amalgamation takes place between the two metals, and the plate becomes of a beautiful bright silver appearance. If the zinc thus amalgamated be again put into the dilute acid, there is no action, for the mercury retains the zine with sufficient force to protect it from the acid. If a piece of copper be immersed along with the zinc, and the two metals be made to containing a mixture of about 15 or 20 (Morhydrogen gas is at the same time evolved from its surface. If the zinc be taken out, common salt next the zinc, and a solution of sulphate of copper next the copper in the porous cup, if a strong current ent be be desired.

The liquids inside and outside the porous cup should stand at the same level. Dilute sulphuric acid (1 part acid to 10 water) makes a very constant, but weaker current. 3667. Description of a Smee's Battery. This apparatus consists of a vessel fit gives only 7) parts water to 1 part sulphuric acid, provided with a strip of baked and varnished wood, long enough to stand touch each other, a particular influence is induced among the three elements, zinc, copper, and acid; and the acid again acts upon the zinc as if no mercury was upon it, but the across the edge of the vessel, and grooved hydrogen is now seen to escape from the sur- lengthways underneath, to receive the edge of / ELECTROTYPING. a silver plate, to which a short wire is at- is sold), and pour into it a mixture of 21 parts tached and connected through a hole in the water and 1 part sulphuric acid, until the wood with a screw cap on the upper side of diluted acid in the porous tube stands at the the wood. Two plates of zinc are arranged, same level as the sulphate of copper solution one on each side of the strip of wood, and outside it. To one end of a piece of copper secured by a screw clamp , the upper part of wire fasten a strip of amalgamated zinc (see which is also fitted with a screw cap. The No. 3662), which is to be inserted in the object of the screw caps is to receive and porous tube; to the other end of the wire secure the wires connecting with the decomposing cell. The zinc plates must first be coated with amalgam (see No. 3662, also No. 3333); and the silver plate must be covered with a coating of platina. (See No. 3670.) The arrangement of the parts will be seen in the cut.

When two or more cells are used in combination, forming a compound battery, the silver plate of the first cell is connected by a wire with the zinc plates of the second; the silver plate of the second cell is connected with the zinc of the third cell; the silver of the third with the zinc of the fourth, and so on through any number of cells.

The two wires connecting the battery with the decomposing trough are attached, one to the zinc plates of the first cell, and the other to the silver plate of the last cell. In fact, the zinc pole of the first, and silver pole of the last cell, really constitute the battery, the intermediate cells each furnishing an additional quota, as it were, of intensity, to the galvanic current.

The wire connected with the zinc (or positive) plates is called the negative pole or cathode; and the wire connected to the silver (or negative) plate is called the positive pole or anode. The material used for connecting wires is usually copper, and should be clean and bright, and in order to insure perfection of contact, the ends of the wire may be amalgamated by dipping, first in a solution of nitrate of mercury, and then in metallic mercury. 3668. Improved Liquid for the Galvanic Battery. Mr. Victor Barjon's new battery liquid is made by mixing a solution of bichromate of potash with a little lime, and with sulphuric acid. He puts 2 pounds bichromate of potash into a gallon of boiling water, and lets the solution cool down to 68°, and adds 2 ounces of lime. After stirring, he adds sulphuric acid until the gravity reaches 35° Baumé. Then, having stirred the whole, he lets it stand for 24 hours, when it is ready for use. attach the object to be electrotyped, properly prepared (see No. 3689), and place it in the copper solution, with its face parallel to the zinc plate, and about 1/2 an inch from the side of the porous tube. In about 24 hours the deposit of copper will be of about the thickness of a card, and may be taken off. When not in use, the zinc should be taken out, washed and dried; and when in use must on no account touch the bottom or any other part of the porous tube. It is a good plan to give the wire one twist round a stick of wood, laid across the top of the tube, so as to suspend and support the zinc. A few crystals of sulphate of copper, enclosed in a piece of lawn or net, should be hung from the edge of the vessel just below the surface of the copper solution, to replace the copper that deposits on the object being electrotyped, and prevent the solution from becoming weaker.

3670. Το Coat Silver with Platina.

This is effected by the one cell process, substituting for the sulphate of copper solution, water acidulated with sulphuric acid, and containing a little chloride of platinum. The silver is first roughened on the surface by applying strong nitric acid, and washed; it is then attached to the end of the wire leading from the zinc plate in the porous cell, and immersed in the platinum solution exactly as if it were a medal to be electrotyped, until the surface is covered with a dark and granular deposit.