Electrum

“ Since the ions which carry the current have to travel all the way from one electrode to the other, any obstacle which is impervious to these ions will, if placed between the electrodes, stop the current to the electrode where there is no ionization. A plate of metal will be as effectual as one made of a non-conductor, and thus we get the remarkable result that by interposing a plate of an excellent conductor like copper or silver between the electrode, we can entirely stop the current. ”

“ Metals; Electric Positive-Negative.—To understand the principle, it may be stated that all metals are electrically positive-negative to each other. You will remember that it has hereinbefore been stated that if, for instance, iron and copper are put into an acid solution, a current will be created or generated thereby. So with zinc and copper, the usual primary battery elements. In all such cases an electrolyte is used.
Thermo-electricity dispenses with the electrolyte, and nothing is used but the metallic elements and heat. The word thermo means heat. ”

“ It seems tolerably clear from all the facts of electrolysis that electricity can only pass through a conducting liquid or electrolyte by being carried on atoms or groups of atoms which are called ions—i. e., wanderers. The quantity thus carried by a hydrogen atom or other monad element, such as sodium, silver or potassium, is a definite natural unit of electricity. The quantity carried by any other atom or group of atoms acting as an ion is always an exact integer multiple of this natural unit. ”

“ Electricity and Chemical Action. We have just seen, Chapter VII., that the electric current has the power to decompose certain compounds when they are in solution. By choosing the right solutions, then, we shall be able to get copper, silver, and other metals set free by electrolysis.
82. Electroplating consists in coating substances with metal with the aid of the electric current. If we wish to electroplate a piece of metal with copper, for example, we can use the arrangement shown in Fig. 78, in which C is the cathode plate to be covered, and A is a copper plate. ”

“ 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. ”

“ In the first form there is, on the whole, no chemical work done in the electrolytic process. The system consisting of two copper electrodes and cupric sulphate as the electrolyte is an example of such a voltameter. The weight of the copper deposited on the cathode measures the current.
The second form depends for its indications on the evolution of gas, the volume of which is measured. The water voltameter is a type, and is the form especially used. The gases evolved are either collected together, or the hydrogen alone is collected. ”

“ In this way the electrons at the far end of the wire commence to move at practically the same moment as those near the battery.
It has been a source of amusement to me to see people perfectly mystified by the fact that they can get no electric current unless they have a complete circuit. What else could they expect? How could man march if he had no road to march on? You see, the reason for our march is that we wish to escape from the overcrowding on the zinc, and we are forced towards the copper. ”

“ To-day we have definite experimental proof that negative electricity is composed of separate particles or units. Just as matter is composed of invisible atoms, so also is negative electricity of an atomic nature. These particles of negative electricity have been christened electrons, electron being the Greek word for amber, from which man first obtained electricity. Of course no one can ever hope to see an electron, but physicists have been able to determine its size and mass, its electric charge, and the speeds at which it moves. ”

“ If, when a hot metal is emitting ions in a rarefied gas, an electromotive force be established between the metal and a neighbouring electrode, either the positive or the negative ions are urged towards the electrode by the electric field, and a current is thus transmitted through the intervening space. ”

“ Therein is made the first known suggestion as to the chemical origin of voltaic electricity, inquiring whether the phenomenon of galvanism is not solely due to chemical affinities of which electricity may be one of the concomitant effects, and also ascribing the violent convulsions in a frog to a chemical change which is produced by the contact of one of the metals with some liquid matter on the animal’s body, the latter decomposing and allowing its oxygen to combine with the metal. ”

“ If such an electrolytic cell has a continuous electromotive force applied to it tending to force a current through the electrolyte from the platinum wire to the lead plate, we can distinguish three stages in its operation, which are determined by the electromotive force and the inductance in the circuit. First, if the electromotive force is below sixteen or twenty volts, then ordinary and silent electrolysis of the liquid proceeds, bubbles of oxygen being liberated from the platinum wire and hydrogen set free against the lead plate. ”

“ We go a step further, and find that we can decompose metals as well as liquids, and that we can make a pure metal out of an impure one, as well as make the foulest water pure. But we shall also, in the course of our experiments, find that a cheap metal can be coated with a costly one by means of electricity—that we can electroplate by electrolysis. ”

“ Two metals outside of the solution contained in a primary battery cell, but under differing physical conditions from each other, will yield a current. A piece of polished iron and a piece of rusty iron, connected by a wire, will yield a small current. Rusty lead, so to speak, so connected with bright lead, has a high electromotive force. Oxygen makes lead rusty, and hydrogen makes it bright. Oxygen and hydrogen are the two gases cast off when water is subjected to a current. ”

“ While electrolysis fully establishes the close relationship between electrical phenomena and those of chemical combination, the fact that every chemical compound is not an electrolyte shews that chemical combination is a process of a higher order of complexity than any purely electrical phenomenon. Thus the combinations of the metals with each other, though they are good conductors, and their components stand at different points of the scale of electrification by contact, are not, even when in a fluid state,, decomposed by the current. ”

“ From this we conclude that the electrification of the resin is exactly equal and opposite to that of the glass. By putting in any number of bodies, electrified in any way, it may be shown that the electrification of the outside of the vessel is that due to the algebraic sum of all the electrifications, those being reckoned negative which are resinous. We have thus a practical method of adding the electrical effects of several bodies without altering the electrification of each. ”

“ A strong battery produces heat in such a degree that all metals can be melted. Light is produced in flashes, or if the end of the leading wires are connected with two pencils of hard carbon, and brought very near together, then a brilliant light, or arc, called the voltaic arc, is produced. This is the dazzling bright light which we call electric light. The chemical effect of a current in decomposing compound substances is called electrolysis. In this way water can be decomposed into its compounds, hydrogen and oxygen; copper sulphate into sulphur and metallic copper, etc. ”

“ In the same way Professor Hesehus has explained how contact electrification is produced, by the tendency of bodies to equalise their superficial properties by means of a transport of electrons, and Mr Jeans has shown that we should discover the existence of the well-known laws of distribution over conducting bodies in electrostatic equilibrium. A metal can, in fact, be electrified, that is to say, may possess an excess of positive or negative electrons which cannot easily leave it in ordinary conditions. ”

“ Each has a higher potential than the acid, but their potentials are not the same. This electrification tends to pass from the place of higher to the place of lower potential, and the conducting wire allows this transfer to take place. As the difference of potential is kept up by the continued chemical action, the current is continuous, and not simply instantaneous, as in discharges of frictional electricity. As heat is produced by the burning of coal, so electrification is produced by the chemical burning of zinc. ”

“ The results of these experiments show a remarkable difference between the property of positive and negative electrification, for the positive electricity, instead of being associated with a constant mass 1/1000 of that of the hydrogen atom, is found to be always connected with a mass which is of the same order as that of an ordinary molecule, and which, moreover, varies with the nature of the gas in which the electrification is found. ”

“ If the metal conducting wire ends in the cathode of a vacuum tube, the electrons carried through the wire pass freely into the tube as cathode rays from the cathode.
This motion of electricity agrees best with the one-fluid theory, since the electrons, which here alone accomplish the passage of the electricity, may be considered as the fundamental parts of electricity. In this respect the choice of the terms positive and negative is very unfortunate, since a body with a negative charge actually has a surplus of electrons. ”

“ The arrangement of metals and acid which we have described is termed a voltaic couple, element, or cell; and a great controversy has long been carried on among men of science as to the place at which the development of electricity has its origin. Three-quarters of a century ago, the effect was attributed by Volta to the mere contact of the two dissimilar metals. In the experiment we have described this contact, supposing the wires to be of copper, would occur at the junction of the wire and the zinc plate. ”

“ Electrons, however, which, on arriving at the surface of the metal, possessed a kinetic energy superior to this work, might be shot forth and would be disengaged as a vapour escapes from a liquid. Now, the number of these rapid electrons, at first very slight, increases, according to the kinetic theory, when the temperature rises, and therefore we must reckon that a wire, on being heated, gives out electrons, that is to say, loses negative electricity and sends into the surrounding media electrified centres capable of producing the phenomena of ionisation. ”

“ Electricity as first Obtained by Man. Until modern times the only electricity known to us was that of the lightning flash, which man could neither hinder nor make. But in the year 1800, electricity in the form of a weak current was obtained by Volta of Italy in a very simple way; and even now our various electric batteries and cells are but a modification of that used by Volta and called a voltaic cell. A strip of [307] copper and a strip of zinc are placed in a glass containing dilute sulphuric acid, a solution composed of oxygen, hydrogen, sulphur, and water. ”

“ In the same way each molecule of the anion when liberated, communicates to the anode a charge of negative electricity, the numerical magnitude of which is the same as that of the positive charge due to a molecule of a cation, but with sign reversed.
If, instead of a single molecule, we consider an assemblage of molecules, constituting an electrochemical equivalent of the ion, then the total charge of all the molecules is, as we have seen, one unit of electricity, positive or negative. ”

“ All bodies are not, however, equally good electrics; shell-lac, [Pg 197] amber, resins, sulphur, and glass, exhibiting more powerfully the phenomena of frictional or mechanical electricity, than the metals, charcoal, or plumbago. Solid bodies allow this peculiar principle to pass along them also in very different degrees. Thus electricity travels readily through copper and most other metals, platinum being the worst metallic conductor. It also passes through living animals and vegetables, smoke, vapour, rarified air, and moist earth ”

“ The electrolytic rectifier is based upon the fact that if plates of aluminium and carbon are placed in an electrolyte, say a solution of alum or dilute acids which yield oxygen on electrolysis, it is found that a current can be sent through the liquid from the carbon to the aluminium, but that great counter electromotive force is created to a current in the opposite direction. ”

“ When positive and negative electricity are present in equal amounts in a body, they neutralize each other from the point of view of the outside world, and the body appears as unelectrified. When a body appears as electrified, that is because there is a preponderance of one kind of electricity. The hydrogen atom, when it is unelectrified, consists simply of a hydrogen nucleus with one electron. ”