Dust Bands
Thin metal bands or guards which are inserted between the upper and lower plates of a movement to exclude all dust.
EARNSHAW, THOMAS. A celebrated watchmaker of London, who was born at Ashton-under-Lyne, Lancashire, in 1749, and died in 1814. He was the inventor of the spring detent escapement and the compensation balance, both substantially as now used in chronometers. He made his improvement in the spring detent in 1781. He presented a petition to the Board of Longitude for aid in 1791, and again in 1797. He received his long-contested reward, Dec. 27, 1805.
EAST, EDWARD. A celebrated watch and clockmaker of London. He was one of the ten original assistants appointed by the Charter of Incorporation of the Clockmakers' Company in 1632. Was Warder in 1638-9, Master in 1645-52, Treasurer in 1637, being the only occupant of the latter office in the history of the company. He was watchmaker to Charles I.
ELECTROPLATING, BRONZING AND STAINING. The first requisite in attempting to do electroplating in a small way is to understand the battery and to select one that will give an electric current of the proper intensity and quantity for the required time, without too much care and attention on the part of the workman. Were he provided with measuring instruments, so that he could readily determine when his current was changing in quantity and power, the choice of a battery would not be of so much importance; but volt meters and ampere meters are too expensive to be possessed by the average man who does plating in a small way, and he is necessarily obliged to depend on theory in arranging his forces and judge of the results by the appearance of his work in the bath. Hence it is important that he should have an understanding of the nature of the action in the battery and be able to maintain the requisite conditions from the appearance of the battery itself.
Without attempting to give too close a definition, electricity may be defined as a force or energy which is the result of a displacement of the normal balance of forces between two elements in close connection with one another. This normal force is called the potential of its element, and if two elements having different potentials, are connected together and placed in a fluid which will produce chemical action upon one or both, the result will be a flowing of energy through the connection to the element having the lowest potential. This will be kept up as long as the chemical action continues and the connection between the two elements remains unbroken. It will be readily seen that, owing to the varying potentials of the different elements, the varying facility of the conductors used to connect them, and the varying intensity of chemical action in the solution employed, the electrical current will vary in strength (or voltage) in different batteries, and in quantity, according to the size of the elements and the freedom with which they are attacked by the solution.
Voltage is the measure of strength or intensity of the current and depends upon the difference of potentials of the elements and the kind of chemical action between them. It is the same for the same combination, regardless of the size of the elements. Thus, a battery the size of a thimble has the same voltage as one the size of a door, if the elements and solution are the same. We have not the space to explain this at length, but will simply state that the volt is the recognized unit of the measurement of strength of electric currents.
The ampere is the unit of measurement of the quantity of currents. Amperage depends on the size of the elements; and the available amperage depends on the size of the conductors and the freedom of action between the elements. Amperage is consumed by doing work or by the heating of insufficient conductors, or by undue resistance in the battery, just as power is consumed in turning steel, or in running shafting, or overcoming the resistance caused by friction of boxes on a shaft that is run without oil. Strictly speaking, if the voltage or intensity of the current be sufficient to do the work required, then the amperage is the force used to do the work, and it is destroyed by that work and the chemical or electrical resistance, just as mechanical power is consumed in running a lathe or doing any other work. From this, it follows, that in order to operate economically, extreme care should be taken that the connections be large enough to carry the current easily; that the solution be kept in perfect order, both in the battery and the plating vat; and that all joints be kept bright and firm so as to insure perfect contact and offer no resistance to the passage of the current.
The current always flows from the element having the highest potential (called the + or positive pole) along the wire and through the solution in the plating vat, to the other wire, and thence to the negative pole, carrying with it in passing through the solution, particles of metal from the anode and depositing it on the article to be electroplated (called the cathode); hence care should be taken to always get the cathode affixed to the negative (-) pole of the battery, in order that it may receive the deposit.
Electrical resistance is that property of conductors (wires, solutions, objects, etc.) by which they tend to reduce the intensity of a current passing through them. The practical unit of resistance is the ohm. The number of amperes of current flowing through a circuit is equal to the number of volts of electro motive force, divided by the number of ohms of resistance in the entire circuit, that is from positive pole clear through wires, solution and battery, back to the starting point. Thus it will be seen that if the resistance be greater than the voltage of one cell will overcome, no current will flow, and the voltage must be increased to such an amount as will allow the desired quantity of current to pass. This is done by coupling cells in various ways, which will be explained at length further on. The resistance of a conducting wire is directly proportional to its length, and inversely proportional to the square of its diameter; hence it follows that the short and large wires cause less loss of current than smaller and longer ones.
In all batteries the resistance increases with the distance between the elements, and decreases when the immersed surfaces are increased. The resistance is also increased by the bubbles of hydrogen liberated at the positive pole sticking to it in great numbers. Hydrogen is a nonconductor and prevents the action of the solution on the metal. When this takes place to such an extent as to stop chemical action altogether, no current will pass and the battery is said to be polarized.
These remarks are intended to aid in the intelligent selection of batteries, etc., those who, having to deal with such apparatus, yet have never had the opportunity to study an electrical treatise. We are often asked: What is the best battery? We can only answer: There is no best battery; that is, no battery is suited to all kinds of work. That which is best in one case may be worst in another. The suitability of a battery for any special purpose depends on what is called its constants, i.e., electro-motive force and internal resistance. In order to be really perfect a battery should fulfill the following conditions: 1. It electro-motive force should be high and constant. 2. Its internal resistance should be small. 3. It should give a constant current and must therefore be free from polarization, and not liable to rapid exhaustion, requiring frequent renewal of material. 4. It should consume no material when the circuit is open. 5. It should be cheap and of durable materials. 6. It should be manageable and, if possible, should not emit corrosive fumes. No single battery fulfills all these conditions, however, and, as we have already intimated, some batteries are better for one purpose and some for another. Thus, for telegraphing through a long line of wire, a considerable internal resistance is of no great consequence, as it is but a small fraction of the total resistance in circuit. For electric gas lighting or other low resistance circuits, on the other hand, much internal resistance would be, if not absolutely fatal, certainly a positive disadvantage. The most reliable batteries for electroplating work are the Daniel, Gravity, Bunsen, Smee and Carbon, which we will accordingly describe in their order. The Daniell, Fig. 118, consists of a glass or stoneware jar, containing a cylinder of copper surrounding a porous clay cup, in which stands a cylinder of zinc. At the upper part of the copper sheet is a pocket of perforated copper, which is filled with crystals of sulphate of copper. The object of the pocket is simply to hold the sulphate up to the top of the solution, so that it will dissolve more readily, and any other method would do as well. In charging this battery, the glass vessel and the porous cup are filled with water, and crystals of sulphate of copper are put in the pocket. If wanted for immediate use, a small quantity of sulphate of zinc may be dissolved in water and added to the porous cup; if not wanted immediately, the battery may be short circuited by connecting the zinc and copper elements by a piece of copper wire, and it will attain its full strength in ten or twelve hours. A little sulphuric acid dropped in the porous cup will answer just as well, if sulphate of zinc is not on hand. The chemical action of this battery is as follows: The zinc decomposes the water, forming oxide of zinc and liberating the hydrogen. The oxide of zinc attacks the sulphate of vitriol, depriving it of the acid, which forms sulphate of zinc, and leaving it as oxide of copper; the oxide of copper is thereupon attacked by the hydrogen, which combines with the oxygen and forms water, while the metallic copper falls to the bottom as a fine powder. It will thus be seen that action is simple and continuous, no fumes are given off, and all that is required to maintain the action is a regular supply of copper sulphate to keep the fluid in the outer jar, near the point of saturation. The most prominent fault of this battery is the tendency of the copper to fill the pores of the cup, and thus decrease the action of the battery. It can be partially prevented by coating the bottom and about a quarter of an inch of the sides of the porous cup with wax, and brushing off the deposit as fast as it is formed. The battery should not be allowed to stand on open circuit without the zinc element being removed, and the sulphate of zinc solution in the cup should not be heavier than 25 degree B, nor lighter than 15 B. If these precautions are observed, the battery should give a constant and free current as long as any zinc remains. Its' electro-motive force is about 1.07 volt, and a gallon cell will give about one-half ampere, when in good order, on a short circuit. Its internal resistance varies, but should not be allowed to exceed three to five ohms.