The cover has a separable hinge, which permits its entire removal when open and facilitates charging the batteries in "banks." ers and cases, equipped with self-contained locks, are interchangeable. The two cells are connected in series, the positive pole of one and the negative of the other being grounded to their containers, and the containers connected together. The free terminals carry the spiral contact springs, which press against nickeled-steel contact plates in the cover. The contact plates are insulated from the cover and receive the cable terminals. A twin-conductor, rubber-covered cable connects the battery to the cap lamp. At each end the cable is thoroughly armored, preventing injury from sharp bending. While lamp and reflector are being carried in the hand or at other times the armor takes up all the weight, so there is no possibility of strain coming upon the wires at the terminals. An ingenious arrangement permits the easy replacement of the cable should it be cut or otherwise injured in service. The cap lamp consists of a nickel-plated brass reflector provided with a hook to fit into the regulation miner's cap. A tungsten lamp is forced into a spring socket by means of a clip at its tip in such a way that if the lamp be broken the base is immediately disconnected and the lamp extinguished. This safety feature has been thoroughly tested by the Bureau of Mines and unqualifiedly approved under Schedule 6A.

CHAPTER VI

GLOSSARY OF STORAGE BATTERY TERMS

Acid. As used in this book refers to sulphuric acid (H2SO), the active component of the electrolyte.

Acidometer. A hydrometer for testing specific gravity of acid, and specially graduated for that purpose.

Active Material. The active portion of the battery plates; peroxide of lead on the positives and spongy metallic lead on the negatives of lead-plate types.

Alternating Current.-Electric current which does not flow in one direction only, like direct current, but rapidly reverses its direction or "alternates" in polarity so that it will not charge a battery.

Alloy. A mixture of two or more metals produced by fusion, i. e., brass is an alloy of copper and zinc melted together; German silver is an alloy of copper, nickel and zinc.

Ampere. The unit of measure of the rate of flow of electric current. Ampere-Hour.-The unit of measure of the quantity of electric current; thus, 2 amperes flowing for 1⁄2 hour equals 1 ampere-hour.

Anode. The opposite plate to the cathode as the carbon plate of a primary battery. The anode is the terminal the current passes into from the solution.

Antimony. A bright, bluish-white, brittle and easy-pulverized metal combined in small quantities with lead to form a harder alloy suitable for storage-battery plate grids.

Arc-Burning. Making a joint by means of electric current, which melts the metal of the parts to be joined together.

Asphaltum. A natural, tarry substance, not affected by acid, and also an electrical insulator, widely used as a basis for cell-sealing compounds.

Battery.—Any number of complete cells assembled in one set.

Battery Terminals.-Devices attached to the positive post of one end cell and the negative of the other, by means of which the battery is connected to the outer circuit.

Buckling. Warping or bending of the battery plates.

Burning-Strip. A convenient form of lead, in strips, for filling up the joint in making burned connections.

Busbar. A main conductor, usually of heavy section, to which a number of circuit ends having the same characteristics are attached, to save wiring. All positive plates of a storage cell may be said to be attached to a busbar, the negative plates likewise. Instead of having a

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separate conductor coming from each plate and joined to the outer circuit, the plates of a given polarity are grouped by attaching to a busbar. Carbon. One of the chemical elements. A black solid, that may exist as coal, charcoal or graphite, or, after it has been subjected to intense heat and pressure, as a white diamond. A conductor of electricity, having considerable resistance. It is used as a neutral plate in primary batteries, for lead-burning electrodes and for rheostat work. It is not affected by acid. Most of the carbon used in electrical work is manufactured and is not a natural product, as graphite.

Carboy.-A large glass bottle carried in a wooden case for easy handling. Used to hold acid, electrolyte or water.

Cathode. The terminal of an electric circuit from which the current passes into the solution. The zinc plate of a primary battery is a cathode. The cathode is always the element of a battery most acted upon by the electrolyte.

Case. The containing-box which holds the battery cells.

Cell. The battery unit, consisting of an element complete with electrolyte, in its jar with cover.

Cell Connector.-The metal link which connects the positive post of one cell to the negative post of the adjoining cell.

Central Station.-A complete power plant equipped with large dynamos for supplying electric energy to an entire district.

Charge. Passing direct current through a battery in the direction opposite to that of discharge, in order to put back the energy used on discharge.

Charge Rate.—The proper rate of current to use in charging a battery from an outside source. It is expressed in amperes, and varies for different-sized cells.

Chemical Change. The uniting of certain primary or basic substances to form secondary ones, or the breaking apart of complex substances to determine their essential elements. Chemical combination is when elements form a new substance. For instance, hydrogen and oxygen gases combined in the proper proportions will form the liquid we know as water. Decomposition is the reverse of combining elements, Water may be decomposed and hydrogen and oxygen gas liberated by electrolysis.

Chemical Element.-These are basic substances, of which everything in the universe is composed. They may be solid, such as iron, zinc, lead or carbon; they may exist as a gas, such as hydrogen and oxygen, or as a liquid, such as bromine. Some elements combine rapidly with nearly all the others, and some cannot combine except with certain ones. Oxygen is the most active element, and will combine with many of the rest. There are about seventy-five of these elements, though practically everything on earth may be made by various combinations of less than twenty

of them. The process of combining elements is known as "synthesis,' that of separating them as "analysis." The elements which combine together the easiest are the hardest to separate.

Circuits. An electrical circuit is said to be an open circuit when the current cannot flow, and a closed circuit if there is a continuous path for the electricity.

Circuit-Breaker.-An automatic, mechanical, electrically actuated device that takes the place of the fuse and performs the same function in an electric circuit.

Compound Winding.-A method of winding electric machines where both series and shunt windings are incorporated.

Conductor.-A pipe is a conductor of water. If two electrically charged bodies are connected by a piece of wood, glass, rubber, dry cloth, paper or similar materials, there will be no passage of electricity, but if a metal rod is substituted, a current will flow from the body of higher potential to the other. In this case the metal rod or wire is a conductor of electricity. All metals and substances such as acid, water and the various liquids (except oils) conduct electricity so well as to be termed "conductors,'' though it is harder for the electrical current to flow through some kinds of metal than it is for it to pass through others. Copper, aluminum and silver are very good electrical conductors, steel or iron come next in order, while some alloys, such as German silver, offer considerable resistance to the flow of current.

Contact Breaker.-A mechanical switch for closing and opening a circuit in rapid succession.

Controller. A manually or automatically operated device for altering the current flow. Such a device may be interposed between a battery of an electric automobile and the driving motor to vary the speed and power of the latter.

Copper. A reddish-brown metal widely used for electric wires and terminals because of its excellent conductivity. It is employed in many forms of primary battery as the plate of opposite polarity to the zinc element.

Corrosion. The attack of metal parts by acid from the electrolyte; it is the result from lack of cleanliness.

Counter E.M.F.-A potential difference or voltage in a circuit opposed to the main voltage and resisting the flow of the latter. When charging a storage battery, the battery voltage is counter E.M.F. to that of the charging line.

Cover. The rubber cover which closes each individnal cell; it is sometimes flanged for sealing compound to insure an effective seal.

Current. The passage of electricity through any piece of apparatus is termed a current. If the flowing of the electrical charge is continuous it is called a direct current. If the charges are not continuous

but flow always in the same direction it is termed a "pulsating'' current. If an electrical charge flowing in one direction is followed by another charge flowing in the opposite direction, an "alternating" current is produced.

Cutout.-An electro-magnetic mechanism that automatically performs the same function of opening a closed circuit that a hand-operated switch does.

Discharge. The flow of electric current from a battery through a circuit. The opposite of "charge.”

Distilled Water.-The condensed water vapor or steam obtained by cooling vapors given off from boiling water. This will remove the impurities, such as salts, etc. These remain in the still as residue, only chemically pure water being vaporized.

Dynamo. An electrical machine capable of producing current and distributing this current as desired, providing the current is sufficiently strong to overcome the resistance to its motion of the parts comprising the external circuit.

Electrolyte. The fluid in a battery cell, consisting of specially pure sulphuric acid diluted with pure water in some cases and an alkaline solution in others.

Element. One positive group and one negative group with separators, assembled together.

Electric Contact. The joining of two conductors so a current can pass from one to the other.

Electrode. The terminal of any open circuit.

Electrolysis. The separation of a chemical compound into its constituents, by the action of an electric current. It cannot take place unless this compound is a conductor of electricity.

Electro-Magnet.-A bar of iron magnetized by passing a current of electricity through a coil of insulated wire wrapped around it. When the current is interrupted the iron bar or core piece ceases to possess magnetic qualities.

Electrical Distribution.-The action of an electrical machine in regulating the distribution of electricity may be considered to be the same as that of a pump which takes water from one tank and supplies it to another at a higher level. If for these reservoirs we consider bodies insulated from each other, we can, with an electrical generator, take electricity from one that has been overcharged and supply it to another which is undercharged.

Electricity. A force that no one knows the exact nature of. To form some conception of this force, it is well to consider that we are able to place various bodies in different electrical relations. A stick of sealing wax or a hard rubber comb rubbed on a coat sleeve will attract bits of paper, feathers and other light objects. The sealing wax or rub