which, while much less bulky, is more energetic in its action.

If it be desired to start this form of the Daniell battery at once, it is sufficient to add a small quantity of sulphuric acid or of common salt to the water in which the zinc is immersed.

Bunsen's Battery.

The Bunsen battery, which, like the Daniell, is susceptible of many modifications, is shown in its usual form below. It consists of an outer vessel of stoneware or glass, Fig. 43, which is half filled with diluted sulphuric

acid).

acid (about In this is placed a cylinder of amalgamated zinc, furnished with a brass binding screw (Figs. 44 and 45) where a single cell is employed or where it forms one of the terminals of a battery, or with a copper band (Fig. 46) where connection must be made with another couple. Within this comes a porous cup of baked clay (Fig. 47), and within this diaphragm again, a prism of gas-carbon (Fig. 48), with binding screw of one

or the other of the several forms shown in Figs. 49 to 52, according as it is to form the terminal of the battery,

Fig. 46.

Fig. 47.

Fig. 48.

or to be united with the band of a zinc of the adjacent element. Fig. 53 shows the binding screw of a zinc

The wire conductors of copper, for greater precaution, should be insulated by a covering of cotton, silk, caoutchouc or gutta percha, and their extremities alone should be denuded of their insulating covering to permit of making the necessary metallic connections.

The carbon having been placed in the diaphragm, this is filled with strong nitric acid, the proper connections made as before indicated, and the battery is ready for use.

Coupling a Number of Cells.

When several elements are to be connected, they are placed near each other, though without touching, and

the first carbon is left free for the attachment of the wire conductor of the anode. The ribbon or band of the first zinc is bent over and clamped be

tween the jaws of the brass binding screw and the carbon of the second element, and so on, in such a manner that the terminals of the battery will be, at one end a free carbon, and at the other an independent zinc. This zinc, for greater convenience, is furnished with a double binding clamp such as is shown in Fig. 53, from the upper binding post of which proceeds the conducting wire, establishing connection with the objects to be electro-plated.

Fig. 54.

+

Fig. 54 represents a vertical section of a single cell of this description; and Fig. 55 a coupled battery of three cells.

Fig. 55.

Roseleur prefers the use of a small quantity of his amalgamating salt (the formula of which is given further on), as an addition to the sulphuric acid in the outer vessel in which the zinc is placed, to the usual method of amalgamating with mercury direct, since the salt only affects the zinc below the liquid, and the risk of rendering the metallic connections brittle is thereby obviated.

The ordinary usage, however, is to provide a wooden trough sufficiently large to rest one of the zines in it, to place some mercury in the bottom of the trough, and cover it with a small quantity of diluted sulphuric acid. By laying the zincs successively in this trough and turning them around, so that all parts of them shall in turn come in contact with the mercury, they are rapidly and perfectly coated with the metal.

Bringing Batteries into Action.

The battery will generate an electrical current as soon as the circuit is closed; that is to say, as soon as the two extremities of the conducting wires proceeding respectively from the last zinc and the last carbon of the battery, are brought into electrical communication, which may be either by direct contact of the wires, or through the intermediation of a bath or liquid conductor of any description. It will often happen that a battery which appears to be properly set up, will not work. On examination, this will generally be found to be due either to the presence of foreign substances (oxide) preventing clean metallic contacts, or to improper connections in setting up, and the like. Difficulties from these causes disappear on removing the cause.

Before using a battery, it is always necessary to test its working condition. For this purpose, the end of the negative wire should be brought in contact with the terminal

carbon, when, if the battery is working properly, a spark should be seen at the instant contact is made. A similar experiment made with the positive wire should produce the same result. A simpler plan is to rest the ends of the terminal wires a short distance from each other upon a piece of battery carbon or upon a file, and then to scrape with one wire over the surface while the other remains. in contact. Numerous sparks should immediately appear. When one element of a battery is wrongly put up, the defect may be located by successively presenting the end of the negative wire to the carbon of each element. That which does not produce a spark belongs to the defective element.

"

A common cause of the stoppage of the current is an excessive porosity of the porous cells. This will generally be indicated by the deposition of a whitish coating of zinc salt upon the surface of the carbons, which speedily checks the flow of the current. When this defect is observed, it is necessary to substitute a fresh porous cell for the defective one, and to thoroughly remove the deposit from the carbon by scraping. This state of things is generally observed only after the battery has been working for several days without renewal of the liquids, or when the same has been too strongly acidulated.

It may also happen that the battery will cease working from too great an accumulation of sulphate of zinc, which, when the solution becomes saturated, crystallizes upon the zinc, and prevents any further action. The acid solution is then removed, a fresh one substituted, and the zine cleaned and returned. Rolled zinc is preferable to cast.

Keeping the Battery in Order.

Every twenty-four hours, and sometimes oftener, the losses of the battery must be made good by adding, with