Electric cell

“ When the new compounds are allowed to go back to their original condition by joining the electrodes of the charged cell a current is produced. In other words, an electric current [157] produces chemical changes in the cell by electrolysis, and these new compounds have an E. M. F. of polarization because they are constantly willing and anxious to get back to their old state. The plates are lead and are usually coated with compounds of lead. Hydrogen and oxygen are given out at the electrodes. The current from a dynamo is used to charge secondary batteries. ”

“ The simple cell polarizes rapidly, so something must be used with the dilute sulphuric acid to destroy the hydrogen bubbles. This is done in the bichromate of potash cell.
In order to get complete depolarization—that is, to keep the carbon plate almost perfectly free from hydrogen, it is necessary to use two-fluid cells, or those to which some solid depolarizer is added to the one fluid.
50. Open and Closed Circuit Cells. If we consider a voltaic cell, the wires attached to it, and perhaps some instrument through which the current passes, we have an electric circuit. ”

“ This increases the resistance of the electrolytic cell. If, however, one electrode of this cell is connected to the earth and the other to a receiving antenna and electric waves allowed to fall on the antenna, the oscillations passing through the electrolytic cell will remove the polarization and temporarily decrease the resistance of the cell. This may be detected by putting a telephone in series with the electrolytic cell, and then on the impact of the electric waves a sound is heard in the telephone due to the sudden increase in the current through it. ”

“ If the wires are connected to an electric bell, the bell will ring, or, instead, the current may be used to run a small motor. If the cell is made of two zinc plates or two copper plates, the bell will not ring, because no electricity will be produced. In order to produce a current, the electrodes must be made of two different materials upon which the acid acts differently. Current may be obtained from a cell made with a zinc and carbon plate or from one with zinc and iron. ”

“ During a small electric transfer through the cell, the external work done is Ee, where E is the electromotive force. If the chemical changes which occur in the cell were allowed to take place in a closed vessel without the performance of electrical or other work, the change in energy would be measured by the heat evolved. Since the final state of the system would be the same as in the actual processes of the cell, the same amount of heat must give a measure of the change in internal energy when the cell is in action. ”

“ Molten wax, or a suitable composition, is then poured on top of the contents of the cell to seal it up and prevent the evaporation of the fluid. A terminal on the carbon rod and another on the zinc case complete the cell.
Fig. 4
The voltage of both the Leclanche and the dry cell is about 1.45, when it goes below this it indicates that the cell is worked out.
The two cells described are known as open-circuit cells and are only intended for intermittent working.
When a current is needed for a long period at a time a closed circuit cell should be used, such as the gravity Daniell cell. ”

“ They become charged by chemical action, and not by friction. The zinc is gradually dissolved, and it is this chemical burning of the zinc that furnishes energy for the electric current in the simple cell. The electrification, or charge, on the plates tends to flow from the place of higher to the place of lower potential, just as water tends to flow down hill. If a wire be joined to the two metals, a constant current of electricity will flow through it, because the acid continues to act upon the plates. The simple cell is a single-fluid cell, as but one liquid is used in its construction. ”

“ The electricity excited by the action on the zinc in one cell is carried on to the next, and that again excites and transfers an additional quantity to the third cell, thus increasing in intensity to the last pair of plates in the series. The electric current, as it is called, passes along the wire, and whether the wire136 be one yard, or whether it be a hundred miles long, the generation of electricity takes place the instant that the circuit is completed, and ends the instant that the circuit is broken. ”

“ The polarization at the surface of the electrodes will set up an opposing electromotive force, and the unequal dilution of the solution will turn the electrolyte into a concentration cell and produce a subsidiary electromotive force either in the same direction as that applied or in the reverse according as the anode or the cathode solution becomes the more dilute. Both effects thus involve internal electromotive forces, and prevent the application of Ohm’s law to the electrolytic cell as a whole. ”

“ The light is not actually transmitted, but only its effects. Suppose a picture is laid off into small squares and there is a selenium cell corresponding to each square and for each selenium cell there is a wire that runs to a distant station in which circuit there is a battery. At the distant station there are little shutters, one for each wire, that are controlled by the electric current and so adjusted that when the cell at the transmitting-end is in the dark the shutter will be closed. ”

“ Faraday established the fact that in certain processes there was more than a hint that electricity was always present in multiples of a definite unit. In the process called electrolysis the electric current is driven across a cell full of liquid containing molecules of some substance. When the electricity passes there is a loosening of the bonds that bind together the atoms of the molecule, and a separation; atoms of one kind travel with the electricity across the cell and are deposited where the current leaves the cell ”

“ Where more than a small amount of current is required, the dynamo and the storage battery have generally taken their place as sources of electric current.
The advantages of voltaic cells as electric generators are: (a) they are inexpensive, (b) they are easily taken from place to place, (c) they may be ready for instant use.
The most desirable voltaic cell would be one having the [Pg 275] following qualities: (a) High electromotive force, (b) no polarization or local action, (c) very low internal resistance, (d) small expense, both as to first cost and upkeep.
Fig. ”

“ Minchin also, working at Cooper’s Hill with his sensitive photo-electric cells, especially with some which he called “impulsion cells,” that behaved abnormally when subjected to taps or other mechanical vibrations, found that when Mr. Gregory was working a Hertz radiator in another part of the same laboratory the electrometer connected to his cells responded. ”

“ For instance, if a number of electrolytic cells of dilute sulphuric acid with platinum electrodes are arranged in series, and if a small electromotive force, such as that of one Daniell's cell, be made to act on the circuit, the electromotive force will produce a current of exceedingly short duration, for after a very short time the electromotive force arising from the polarization of the cell will balance that of the Daniell's cell. ”

“ It is the opinion of several philosophers, that the presence of water is essential in electro-chemical decomposition, and also for the evolution of electricity in the voltaic battery itself. As the decomposing cell is merely one of the cells of the battery, into which particular substances are introduced for the purpose of experiment, it is probable that what is an essential condition in the one case is more or less so in the other. ”

“ When connecting cells in multiple those of the same kind should always be selected. Any cell whose electromotive force is not fully equal to the others will absorb energy and be charged by the others. ”

“ If the cells be joined in multiple, the positive poles all being connected by one wire and the negative poles by another, then the currents of all the cells will be added while the electromotive force of the combination remains the same as that of a single cell, assuming all the cells to be alike in electromotive force. ”

“ In renewing dry cells (or any other kind of cell) , a greater number should never be put in series than was originally required to do the work, because the additional cells increase the voltage beyond that required, which causes more current than is necessary to flow through the coil. This increased current flow shortens the life of the battery. 2. In connecting dry cells in places where there is vibration, heavy copper wire should not be used, because vibration will cause it to break. ”

“ No cell will remain forever without chemical action, yet a dry cell which might use up its zinc and ammonium chloride in a few hours [256] if the circuit is closed may be kept idle three or four years, and still be able to furnish electricity enough to ring a bell. Some persons feel defrauded if the author of a book fails to give them all the new words and conventional terms which belong to any subject. ”

“ What is positive and what negative electricity?
No difference in electricity in itself. When a body has more than its natural amount of electricity, it is said to be charged positively; when it has less than its natural amount it is negatively charged.
What is a Cell; what a Battery?
If a piece of zinc and copper joined by a wire be dipped in a liquid—generally weak sulphuric acid—which will act chemically on the metals, a current is produced. Such an arrangement is called a couple, or cell. If many cells are connected, then it is called a battery. ”

“ This of course means making the cell larger, and very large cells take up a lot of room and are troublesome to move about. We can get the same effect however by coupling. If we connect together all the positive terminals and all the negative terminals of several cells, that is, copper to copper and zinc to zinc in Daniell cells, we get the same result as if we had one very large cell. The current is much larger, but the electro-motive force remains the same as if only one cell were used, or in other words we have more amperes but no more volts. ”

“ Yet in cases in which the mixture of more and less concentrated solutions is not attended with evolution or absorption of heat, the electromotive force must vanish in a cell of the kind considered, if it is determined simply by the diminution of energy in the cell. ”

“ If no changes take place in the cell except during the passage of the current, and all changes which accompany the current can be reversed by reversing the current, the cell may be called a perfect electro-chemical apparatus. The electromotive force of the cell may be determined by the equations which have just been given. ”

“ The researches of M. Gaston Planté on the polarization of voltameters led to his invention of the secondary cell, composed of two strips of lead immersed in acidulated water. These cells accumulate, and, so to speak, store up the electricity passed into them from some outside generator. When the two electrodes are connected with any source of electricity the surfaces of the two strips of lead undergo certain modifications. Thus, the positive pole retains oxygen and becomes covered with a thin coating of peroxide of lead, while the negative pole becomes reduced to a clean metallic state. ”

“ Be the true explanation what it may, the fact is undoubted that by joining cell to cell, we can really obtain vastly more powerful effects. If we take a single cell, such as that represented in Fig. 256, and connect the plates with a long and thin wire, we shall find 494that the current flowing through each part of the circuit is much weaker than when we connect the plates with a short and thick wire. In other words, the action in the latter case, when the wire is stretched over a magnetic needle, will be more powerful than in the former. ”

“ We may connect an insulated line to a source of such currents, we may pass an inappreciable current over the line, and on any point of the same we are able to obtain a heavy current, capable of fusing a thick copper wire. Or we may, by the help of some artifice, decompose a solution in any electrolytic cell by connecting only one pole of the cell to the line or source of energy. ”

“ If some of the active material has scaled off, it may be forced down to the bottom of the jar. If excessive sediment be found, the jar and plates should be washed carefully, and reassembled.
A cell that has been short circuited may be disconnected from the battery and charged and discharged several times separately which may remedy the trouble.
Ques. How are internal short circuits indicated?
Ans. Short circuits in a cell are indicated by short capacity, low voltage and low specific gravity, excessive heating and evaporation of the electrolyte. ”

“ Now, if the secondary cell is separated from the primary one, we have a veritable voltaic battery, for the symmetry of the poles is upset, and one is ready to give up oxygen and the other eager to receive it. ”

“ Making a Dry Cell.—The zinc is the negative, and the carbon the positive electrode. The best material for the electrolyte is crushed coke, which is carbon, and dioxide of manganese is used for this purpose, and the interstices are filled with a solution of sal-ammoniac.
The top of the cell is covered with asphaltum, so as to retain the moistened material and the liquid within the cell, and thus constituted, it is called a dry cell.
Energy in a Cell.—A battery is made up of a number of these cells. ”