Electroplating

“ Practical use of electrolysis is made in electroplating, the production of electrotype blocks for printing, the refining of copper, and the production of metallic sodium and potassium. Electrolysis is also used as a means of storing electrical energy in a chemical form (see Secondary Cell) .
An electric current may be constant in direction (direct current) , or may alternate in direction with a certain frequency (alternating current) . ”

“ 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. ”

“ ELECTROPLATING, the art of depositing metals by the electric current. In the article Electrolysis it is shown how the passage of an electric current through a solution containing metallic ions involves the deposition of the metal on the cathode. Sometimes the metal is deposited in a pulverulent form, at others as a firm tenacious film, the nature of the deposit being dependent upon the particular metal, the concentration of the solution, the difference of potential between the electrodes, and other experimental conditions. ”

“ A powerful lamp uses about 70 feet of rod in 1,000 hours if the arc is exposed to the air. Some lamps have partly enclosed arcs—that is, are surrounded by globes perforated by a single small hole, which renders combustion very slow, though preventing a vacuum.
ELECTROPLATING.
Electroplating is the art of coating metals with metals by means of electricity. Silver, copper, and nickel are the metals most generally deposited. The article to be coated is suspended in a chemical solution of the metal to be deposited. Fig. 84 shows a very simple plating outfit. A is a battery ”

“ Although electroplating or something of the kind is necessary to prevent rust and corrosion, one would be inclined to think that articles which are intended to escape observation would be better adapted to their end if they were protected by some method just a trifle less obtrusive in its brilliancy. ”

“ 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. ”

“ When a liquid like sulphuric acid was electrolysed for a moment with the aid of platinum electrodes, it was found that the electrodes could themselves produce a current when detached from the primary battery. Such a current was attributed to an ``electric polarization'' of the electrodes, and was regarded as having a secondary nature, the implication being that the phenomenon was almost equivalent to a storage of electricity. It is now known that the platinum electrodes stored, not electricity, but the products of electro-chemical decomposition. ”

“ When an electric current is passed through a special battery called an accumulator or reversible battery, chemical changes occur, in that new compounds are formed which possess a reversible capacity; namely, in reproducing the former materials—that is, electricity is generated. This process of forming chemical substances by the passing of an electrical current is called electrolysis and the product so produced is called electrolyte. At the same time it is a known fact that organic chemistry is infinitely more complicated and variable than inorganic chemistry. ”

“ The secondary cell of Planté is an example of a cell made directly by electrolysis, as has been assumed in the preliminary discussion. The electrodes are both lead plates, and the electrolyte dilute sulphuric acid. When a current is passed through the cell, the oxygen evolved on the anode combines with the lead to form peroxide of lead, which coats the surface of the electrode. When the cell is inserted in a circuit, a current is set up, the peroxide is reduced to a lower oxide, and the metallic lead of the other plate is oxidized. ”

“ But, on the other hand, if a few drops of acid be placed in the vessel with the platinum, bubbles of hydrogen appear, and a current flows, zinc dissolving at the anode, and hydrogen being liberated at the cathode. In order that positively electrified ions may enter a solution, an equivalent amount of other positive ions must be removed or negative ions be added, and, for the process to occur spontaneously, the possible action at the two electrodes must involve a decrease in the total available energy of the system. ”

“ An electrode is what we call any piece of metal or wire which is so placed as to let us get at electrons (or 42ions) to control their motions. Let us see how it does so.
To start with, we shall forget the grid and think of a tube with only a filament and a plate in it–a two-electrode tube. We shall represent it as in Fig. 6 and show the battery which heats the filament by some lines as at A. In this way of representing a battery each cell is represented by a short heavy line and a longer lighter line. The heavy line stands for the negative plate and the longer line for the positive plate. ”

“ Those bodies which exhibit electrolysis are always such as have considerable freedom of motion among their molecules. Ordinarily, they are liquids or solids in solution or fused. The discharge through gases is also probably accompanied by electrolysis. Bodies which can be decomposed were called by Faraday, to whom the nomenclature of this subject is due, electrolytes. The current is usually introduced into the electrolyte by solid terminals called electrodes. The one at the higher potential is called the positive electrode or anode; the other, the negative electrode, or cathode. ”

“ The bottom enclosure is the terminal for one electrode, the top enclosure for the other. The electrolyte is a viscous liquid composed of ammonium chloride, zinc chloride, water and starch. Use of the battery causes erosion of the zinc and eventually the mixture leaks through the container. A short circuit, or long continuous use, causes the formation of solids as the zinc is eaten away. The resultant expansion of the cell contents, due to the weakness of the zinc walls, causes bulging, breaking, and seepage. The escaping liquid tends to injure the metal walls of the flash light casing. ”

“ 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. ”

“ If a voltaic battery were constructed of zinc and platina, the latter metal surrounding the former, as in the double copper arrangement, and the whole being excited by dilute sulphuric acid, then no insulating divisions of glass, porcelain or air would be required between the contiguous platina surfaces; and, provided these did not touch metallically, the same acid which, being between the zinc and platina, would excite the battery into powerful action, would, between the two surfaces of platina, produce no discharge of the electricity, nor cause any diminution of the power of the trough. ”

“ The same elegant and correct experimentalist has shown that zinc and platinum wires, one-eighteenth of an inch in diameter, and about half an inch long, dipped into water in which is mixed sulphuric acid so weak that it is not sensibly sour to the tongue, will evolve more electricity in one-twentieth of a minute than is given by thirty turns of a large and powerful plate electrical machine in full action, a quantity which, if passed through the head of a cat, is sufficient to kill it as by a flash of lightning. ”

“ 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. ”

“ 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. ”

“ Since zinc goes into solution and copper comes out, the electromotive force of the cell will be the difference between the two effects. On the other hand, it is commonly thought that the single potential-differences at the surface of metals and electrolytes have been determined by methods based on the use of the capillary electrometer and on others depending on what is called a dropping electrode, that is, mercury dropping rapidly into an electrolyte and forming a cell with the mercury at rest in the bottom of the vessel. ”

“ As the action of the battery proceeds, this amalgam forces its way into the pores of the element and keeps up so good an amalgamation of both copper rod and zinc that zincs can be used up to a point when the rising internal resistance makes it economy to throw them away, and absolutely no perceptible local action takes place in the cell upon continued open circuit. A preparation is furnished if desired, which forms a jelly of the electrolyte, making the cell readily portable. ”

“ Let it simply be noted that such a combination is called a battery; that when the extreme plates of opposite kinds are connected by a wire, a current of electricity passes along the wire from the extreme plate of that metal which is least affected, forming the positive pole, to the other extreme plate of that metal which is most affected and forms the negative pole. The metals commonly employed are zinc and copper, the former being the one most affected by the action of the dilute acid, usually sulphuric acid. ”

“ 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. ”

“ For instance, the electrolyte, being a constant factor, as explained, is not required in any fixed and large amount, as is the case with sulphuric acid in the lead battery; thus the cell may be designed with minimum distancing of plates and with the greatest economy of space that is consistent with safe insulation and good mechanical design. Again, the active materials of the electrodes being insoluble in, and absolutely unaffected by, the electrolyte, are not liable to any sort of chemical deterioration by action of the electrolyte—no matter how long continued.... ”

“ In the same way, any other kind of work done during electrolysis will have an effect on the value of the electromotive force, as, for instance, if a vertical current passes between two zinc electrodes in a solution of sulphate of zinc a greater electromotive force will be required when the current in the solution flows upwards than when it flows downwards, for, in the first case, it carries zinc from the lower to the upper electrode, and in the second from the upper to the lower. ”

“ The patent, a very narrow one in a crowded art, is for a leakproof dry cell for a flash light battery. The conventional dry cell embodies a cup-like zinc electrode acting as a container for a central carbon electrode, electrolyte, and depolarizing mix. ”

“ The most direct evidence of this electrification is furnished by the migration of the colloidal particles through the liquid under the influence of an applied electromotive force. This effect may be well illustrated with colloidal suspensions of arsenious sulphide and ferric hydroxide contained in two U-tubes. The tops of the U-tubes are covered with goldbeaters' skin and are surrounded by wider tubes containing pure water in which platinum electrodes are placed, so that the products of electrolysis collecting around them may not influence the colloid. ”