Description of a Menotti Cell.—A Menotti cell, shown at [Fig. 76], consists of a copper cup containing some crystals of sulphate of copper and covered with a fearnought diaphragm a, placed at the bottom of an ebonite cell b; over this cup is put some sawdust, and resting on top of this is a disc of zinc c on another piece of fearnought. The upper portion of the zinc and its connection with the insulated wire are carefully insulated. Fresh water poured on the sawdust renders the battery active.
Description of a Menotti Test Battery.—[Fig. 77] represents a plan of the top of such a test battery with a 20-ohm galvanometer attached thereto. The connections are made as follows:—
One of the wires w of the object to be tested is attached to the terminal f, which is also connected by an insulated wire to the copper cup a; the other main wire w1 is attached to the terminal g of the galvanometer; h, the other terminal of the galvanometer, is connected by a short piece of wire k to the terminal l of the contact key m; and the contact point n is in connection with the zinc plate c; thus the current from the battery flows along the wire w through the object to be tested, back along the wire w1, through the coils of the galvanometer, along the wire k to the contact key m, and if this is pressed down to the zinc plate c, so completing the circuit.
To steady the needle of the galvanometer a bar magnet is used, which is inserted in the space r. The whole of the apparatus is enclosed in a leathern case fitted with a cover and strap.
This is a very compact and simple form of test battery, and will be found extremely useful in boats, &c., when placing mines in position.
Telegraph Battery.—For the purposes of telegraphing between torpedo stations, &c., a form of Leclanché battery, known as No. 3 commercial pattern, is generally used.
Voltaic Batteries.—The following points in connection with the use of voltaic batteries, which are taken from Beechey's 'Electro Telegraphy,' should be carefully observed:—
1.—Each cell of a battery should be carefully insulated.
2.—The floors and tables in the battery room should be kept scrupulously clean and dry, so as to prevent the least leakage or escape of the current.
3.—The plates of a battery should be clean.