tion. A battery thus disposed may be kept in operation for three weeks, or a month, and sometimes longer.

When this battery is working, the copper of the decomposed sulphate is deposited upon the copper of the vessel, which thus increases in weight and in value. The zinc is slowly dissolved in the solution of common salt, and forms a double chloride of sodium and zinc, of no value.

When two, or a greater number, of Daniell's elements are to be coupled to form a battery, the zinc of the first element is connected with the copper of the second element by means of a well-cleansed metallic ribbon or wire, then the zinc of the second with the copper of the third, and so on, until the whole apparatus (Fig. 33) presents at one end a copper vase, and at the other a zinc plate, unconnected. A metallic wire, or ribbon, connects the anode with the free copper end, and a similar wire is attached to the zinc end and supports the cathode or objects to be electro-plated.

this, the copper solution is placed in the porous cups, from each of which proceeds a copper rod with a perforated

Sur

plate supporting crystals of sulphate of copper. rounding each porous cup is a cylindrical plate of zinc immersed in acidulated water or solution of common salt, contained in a cup of stoneware or glass.

In another modification, much used by electro-gilders of watch- and clock-works, and for telegraphic purposes, each element is composed of

1. A cylindrical vase of stoneware, glass, or porcelain (Fig. 36);

2. A cylinder of zinc to which is soldered or riveted a ribbon of copper (Fig. 37);

3. A porous cell of baked clay (Fig. 38);

4. A glass balloon with a short neck, filled with crystals of sulphate of copper, and closed with a cork perforated with two holes, or having two notches cut on the surface along its length (Fig. 39).

These various parts are united in the following manner

to form a battery: the zinc plate is placed concentrically in the stoneware jar, then the porous cell is introduced.

The copper ribbon of the zinc of the first element dips to the bottom of the porous cup of the next element in such a manner that when several elements are connected there will be at one end a free. ribbon of the last zinc plate, and at the other end a free ribbon extending from the bottom of the last porous cup (Fig. 40). Then, the porous cell and the stoneware jar are filled to the same

level with water. The balloon containing the crystallized sulphate of copper receives as much water as it can hold, and the notched cork being put in place, the balloon is quickly inverted with its neck in the water of the porous cell. The battery is ready to work twenty-four hours after. The ribbon of the zinc end is attached to the conductor which supports the objects to be electroplated, and that of the other end of the cell is connected with the anode. Fig. 41 shows a vertical section of a single cell of the kind just described; and Fig. 42 represents a battery of three such cells.

This form of the Daniell battery operates as follows: the copper sulphate contained in the balloon dissolves in the water surrounding it, and, as this saline solution is denser than water, it descends into the porous cells through one of the notches of the cork, while at the same time an equal volume of the lighter water ascends through the other notch of the cork. In this manner

the sulphate of copper in this balloon is gradually dissolved, and a constant current is established, the denser liquid, more heavily charged with sulphate of copper, descending through one notch of the cork, while the lighter liquid ascends through the other. Simultaneously with the closing of the circuit, chemical action sets in. The sulphate of copper is decomposed, the sulphuric acid passes through the porous cup by exosmose, and acts upon the zinc in the outer vessels, and copper is deposited upon the copper bands in the porous cups, which are connected by conductors, as above described, with the zincs.

In order that this battery may work regularly for six or seven months, it is only necessary to replace the evaporated water. The balloon should be large enough to contain at least several pounds of sulphate of copper crystals, and the zinc cylinders should be from 7 to 8 inches in height and from 4 to 5 inches in diameter. The zinc should be amalgamated, in which case the action, though a little slow at the start, is more regular afterwards. The copper ribbon receives all the metal of the decomposed sulphate, and it sometimes happens that part of the copper becomes deposited on the bottom. of the porous cell, from which it may be removed by aqua fortis. When all the sulphate of copper is used up, the balloons are filled with a fresh quantity of crystals and new copper ribbons inserted to take the place of those rendered too voluminous. This variety of battery is in extensive use, and properly so, for telegraphing and electric signalling. If gilders were will ing to employ such batteries, with elements sufficiently large and numerous, they could dispense with acid batteries which require fresh charging every day; but, whether right or wrong, they still prefer the Bunsen battery,