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Where lamp sockets, receptacles and electroliers, etc., are connected, one-half of the above will be required.

Soldering Fluid (National Board of Fire Underwriters).—The following formula for soldering fluid is suggested.

Saturated solution of zinc chloride - 5 parts.

Alcohol ...... _. 4 parts.

Glycerine 1 part.

Too much care cannot be taken in making joints; a defective joint, although it may not for a time so far lower the insulation as to cause a serious leakage of current, is almost certain to go completely bad sooner or later. (The Elec. Engineer's Pocket Book—Kempe).

Electrical Units.

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Relations Between Electrical and Mechanical Units.—The product of the amperes (current) multiplied by the volts (E. M. F.) and divided by 746 is equivalent to the horse-power developed.

Arc Electrical Lamp.—A 2,000 candle-power "full arc" lamp takes 9.6 amperes, while a "half arc" lamp of 1,200 candle-power takes 6.8 amperes. Arc lamps are usually run at 50 volts. The top or positive carbon burns about V/2 inches per hour, and twice as fast as the lower or negative carbon.

Grounds.—The contact through the earth of both sides of a circuit; this may be produced by escape of current down wet walls, pipes, through trees and other ways.

Incandescent Electric Lamps.—A 16-candIe-power lamp is usually run at a potential of 100 volts and takes about five-tenths amperes; when the lamp is hot it has a resistance of about 168 ohms, hence it takes (E. M. F. -f- R. = C, that is 100-^168 = °-595) about six-tenths amperes to run it.

A 1,000-candle-power arc lamp is usually run at a potential of 50 volts, and takes about 10 amperes.

One indicated horse-power will run 8 incandescent lamps of 16candle-power, or one arc lamp of 1,000 candle-power.

Kinks, Turns, Knots, etc., in wires should be avoided, as they tend to produce overheating by the resistance they offer to the current.

Short Circuit.—A connection between two parts of a circuit, which connection is of low resistance compared to the intercepted portion. A short circuit can be produced by poorly insulated wires against a wet surface, by wires being in contact with metal, by placing poorly insulated wires close together, in flexible cords, etc.

Tubes for wires running through walls and partitions should slope toward.the side of the wall or partition on which the greatest amount of moisture is apt to be.

Care of Apparatus.—As electric light and power apparatus is subject to derangement at all points, and in the great majority of cases, derangements are of the character that can produce fire or serious damage to the apparatus, it is highly necessary, that in plants having more than one dynamo, or in which the installation is large, that there should be in constant attendance, while the dynamos are running, a competent experienced attendant.

No alterations or extensions of systems should be made by any one other than an expert.

DEFINITIONS—Circuit—Included in this are all of the wires and apparatus which form the path for the electric current from and to the generating device, and including the generating device.

Circuit Breaker.—Any appliance or apparatus which will open and close a circuit, hence a switch, a fuse block, a cut-out, etc. While a switch is in fact a circuit breaker it is not commercially termed so, nor is it treated so. Circuit breakers must have noncombustible, non-absorptive bases, with similar covers (when not in approved cabinets); in the construction of the breaker there is a fusible strip or wire of metal which melts upon the over increase of the current, and hence prevents the passing of the current. The object of placing these devices in a circuit is to prevent the overloading of the circuit with electricity.

Closed Circuit.—One in which the current is continuous throughout. By opening a switch or any other device in the circuit, the circuit becomes an open circuit.

Currents, Alternating.—A succession of currents in which there are two directions of flow, t. e., opposite directions, and in which succeeding currents are of short duration, and in opposite directions. Constant.—An unvarying current. "In electric series, incandescent lighting, a constant current is employed and the system is termed as above. In arc lighting systems the constant current series arrangement is almost universal."—(Standard Electrical Dictionary.) Multiphase, Polyphase, Rotary.—Currents produced on a single generator, alternating in a constant proportion of periods.

Electrolysis.—The decomposition of a compound into its elements or its constituents by the action of electricity. The electrolysis of water pipes underground on the line of a trolley line is caused by the return currents acting upon the pipe and "eating it away," or decomposing it.

Potential, Constant.—In which the potential is unchanging. "The ordinary system of incandescent lighting is a constant potential system, an unvarying potential difference being maintained between the two leads, and the current varying according to requirements.'^—(Standard Electrical Dictionary.)

"Potential in electricity is analogous to temperature; and as heat tends to pass from a point at a higher to one at a lower temperature, so electricity tends to move from a higher to a lower potential."—(Century Dictionary.)

"Bushings must be long enough to bush the entire length of the hole in one continuous piece, or else the hole must first be bushed by a continuous waterproof tube, which may be a conductor, such as iron pipe; the tube then is to have a non-conducting bushing pushed in at each end so as to keep the wire absolutely out of contact with the conducting pipe."—(National Board of Fire Underwriters.)

CHAPTER VII.

AUTOMATIC SPRINKLER EQUIPMENT

(All rulings in this chapter are as per rules and requirements of the National Board of Fire Underwriters for the installation of automatic sprinkler equipments, 1901.)

Among all the devices for extinguishing fires in their incipiency, none is so efficient at all times as the automatic sprinkler, for all other apparatus needs the agency cf a person or persons to be of service, whereas this device, being automatically set in action by the agency of heat alone, is always ready for action without any human help.

An automatic sprinkler head is a valve with a seat held in place by fusible solder, and having a deflector for distributing the water in an umbrella-shaped spray evenly over a surface'beneath it of 10 feet, more or less, square. The solder melts at temperatures varying from 165 degs. F. to 360 degs. F., the degree of heat being in accordance with the amount of heat normally in a room; hence in a dry room the degree of the fusing point would be much higher than that in a mercantile risk. The heads are attached to lines of pipe located close to the ceiling, usually from 8 to 11 feet apart, the heads being from 8 to 10 feet apart on the pipes. Water is fed to the pipes from a tank, pump, public water supply, or any other adequate supply. Upon the melting of the solder, the valve seat is released, the valve opened and the water thrown about by the distributor.

There are two systems of automatic sprinklers; the wet system, in which water continually stands in the pipes, for use in buildings in which there is always enough heat to prevent water freezing in the pipes; and the dry system, in which the pipes are filed with air as far back as an automatice valve which is held closed against the pressure of the water by the pressure of the air, and which is located at a point beyond which provision is made against the possibility of the water in the pipe freezing, for use in buildings in which from absence of heat there is a probability of water in pipes freezing.

The following risks especially should be thoroughly equipped with automatic sprinklers: Agricultural implement works, bakeries, boot and shoe factories, candy factories, carriage factories, chair factories, cigarette factories, cotton compresses, cotton mills, cotton seed oil mills, cotton (raw) warehouses, distilleries, flour mills, furniture factories, linseed oil mills, oil cloth works, paint factories, piano factories, power printers and lithographers, rubber works, sash, door and blind factories, saw and planing mills, snuff factories, stamping and tin ware factories, starch works, tanneries, bark mills, wholesale druggists, and all parts of stage section of theaters.

Strongly advised in all manufacturing buildings.

Advised in all buildings.

Before a building is sprinkled, all the needless ceiling, sheathing, hollow siding, tops of high shelves, needless partitions or decks should be removed. Vertical drafts through buildings (such as elevator-ways, well-holes, dummy-ways, chutes, etc.), are detrimental to the proper action of sprinklers and must be "stopped" where practicable.

A maximum protection muft not be expected where sprinklers are at more or less permanent disadvantage, as in the case of stocks very susceptible to smoke and water damage, buildings having deep piles of hollow goods, excessive drafts, explosion hazards, or large amounts of benzine or similar fluid.

DISTRIBUTION OF HEADS—Equipments should thoroughly cover all parts, including all concealed spaces, closets, under and in stairways, blind attics, basements, rope-drives, beltways, pipe, gear and pulley boxes, drying and heating boxes, tenter and dry rooms' inclosures, conveyor trunks, waste pickerdischarge closets, elevator-ways, skylights, shafts, lofts, chutes, . under decks, platforms and half-floors, etc. "Experience teaches that sprinklers are often necessary where seemingly least needed; their protection is required not alone where a fire may begin, but also wherever any fire may extend, including wet and damp locations."

Location of Heads.—To be placed in an upright position wher

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