The Standard Electrical Dictionary Part 119

A paramagnetic substance has high permeability or multiplying power for lines of force, hence in a magnetic field a bar of iron, etc., is in unstable equilibrium unless its longer axis is parallel with the lines of force in order to reduce as much as possible the reluctance of the circuit.

404 STANDARD ELECTRICAL DICTIONARY.

Iron is the most paramagnetic of all substances. Other paramagnetic metals are: Nickel, cobalt, manganese, platinum, cerium, osmium, palladium. Diamagnetic metals are bis.m.u.th, antimony, zinc, tin, mercury, lead, silver, copper, gold, a.r.s.enic. Bis.m.u.th is the most diamagnetic of all metals.

Of gases oxygen is most paramagnetic. Becquerel calculated that a cubic yard of oxygen condensed would act on a magnetic needle as powerfully as 5.5 grains of metallic iron. Liquefied oxygen will adhere to the poles of a magnet.

Changes of temperature and of other conditions may affect a body's magnetism. Thus hot oxygen is diamagnetic, and a substance paramagnetic in a vacuum may be diamagnetic in air.

Of liquids, solutions of iron or cobalt are paramagnetic; water, blood, milk, alcohol, ether, oil of turpentine and most saline solutions are diamagnetic.

Paramagnetism.

(a) The science or study of paramagnetic substances and phenomena.

(b) The magnetic property of a paramagnetic substance; that of being attracted by a magnet, and of arranging itself with its longer axis parallel with the lines of force of a magnetic field.

Parchmentizing.

If cellulose is treated with a mixture of two parts of sulphuric acid and one part of water perfectly cold, it becomes like parchment. It should at once be washed with water, and then with ammonia and water.

The Swan incandescent light fibres are made of parchmentized cotton thread, which is afterward carbonized.

Partial Earth.

A fault in a conductor caused by imperfect connection with the earth, where insulation from the earth is desired.

Pa.s.sive State.

A state of a substance in virtue of which it is unattacked by a solvent which ordinarily would dissolve or attack it. Iron in strong nitric acid is unattacked or a.s.sumes the pa.s.sive state. This particular case is supposed to be due to a coating of magnetic oxide, so that there would be properly speaking no question of a pa.s.sive state, but only one of superficial protection.

The existence of a true pa.s.sive state of any substance is very doubtful.

P. D.

Abbreviation for potential difference or difference of potential, or for electro-motive force.

405 STANDARD ELECTRICAL DICTIONARY.

Peltier Effect.

The thermal effect produced by the pa.s.sage of a current through the junction of two unlike conductors. Such junction is generally the seat of thermo-electric effects, and a current is generally produced by heating such a junction. If an independent current is pa.s.sed in the same direction as that of the thermoelectric current, it cools the junction, and warms it if pa.s.sed in the other direction. In general terms, referring to thermo-electric couples, if pa.s.sed through them it tends to cool the hot and heat the cool junction. The phenomenon does not occur in zinc-copper junctions.

Peltier's Cross.

A bar of bis.m.u.th and a bar of antimony soldered centre to centre at right angles, being notched or halved there to receive or to set into each other. It is used to demonstrate the Peltier effect, q. v. To one pair of ends are connected the terminals of a battery circuit; to the other pair are connected the terminals of a galvanometer.

The galvanometer by its deflections in one and then in the other direction indicates that the junction is heated when the current pa.s.ses from antimony to bis.m.u.th and vice versa. It thus ill.u.s.trates the heating and cooling of a thermo-electric junction by a current of electricity.

The current from the battery by the Peltier effect either heats or cools the junction, as the case may be. This heating or cooling them produces a thermo-electric current in the galvanometer circuit. The battery has no direct influence on the galvanometer.

Pendant Cord.

A double conductor or pair of conductors, insulated from each other and covered with a worsted, silk, or cotton covering and used to suspend incandescent lamps and at the same time to conduct the current to them.

It is also used for other similar service, such as acting as conductors for small motors. Often each conductor is composed of a number of thin wires laid together. This gives flexibility to the cord.

Synonym--Flexible Cord.

Pendulum, Electric.

(a) A pendulum operated by the intermittent action of an electro-magnet, whose circuit is opened and closed by the pendulum itself. A point at the lower end of the pendulum swinging through a globule of mercury may close and open the circuit. Various other methods of accomplis.h.i.+ng the same end are employed ..

(b) A pith ball suspended by a thread from an insulating stand. It is used to show the attraction exercised by a piece of sealing wax or other substance excited by rubbing.

406 STANDARD ELECTRICAL DICTIONARY.

Pen, Electric.

A stylus for producing a series of perforations in paper, so that the paper may act as a stencil for the reproduction of a great number of copies of the original matter. Various kinds of electric pens have been invented. One kind, invented by Edison, consists of a handle carrying an electric motor actuating a needle, which is driven in and out of the other end of the handle with high rapidity. It is used by being held vertically on the paper with the needle end downward, and is moved so as to describe perforated letters or designs. The paper is then used as a stencil with an ink roller to reproduce the writing or design ad libitum. A simpler kind dispenses with the motor and depends on the perforations produced by the electric spark. As shown in the cut the stylus is one terminal of an induction coil circuit. The support on which the paper rests is the other terminal and must be a conductor. In use the induction coil is started, and the stylus is moved over the paper; a series of sparks pa.s.s through the paper from stylus to the supporting tablet, perforating the paper and producing a stencil to be used for reproduction.

Fig. 256. ELECTRIC PEN.

Pentane Standard, Harcourt's.

A standard of illuminating power; in it the combustible substance is a gas made by mixing one cubic foot of air with three cubic inches of liquid pentane, measured at 60? F. or, if measured as gases, 20 volumes of air to 7 of pentane. It is burned at the rate of 0.5 cubic foot per hour from a cylindrical tube one inch in diameter, closed at the top by a disc 0.5 inch thick with a hole 0.25 inch in diameter, through which the gas issues. It gives a flame 2.5 inches high.

The pentane used is the distillate of petroleum which boils at 50? C.

(122? F.) ; it has a specific gravity at 15? C. (60? F.) of from 0.628 to 0.631. It is almost pure pentane (C5H12).

As long as the rate of consumption is between 0.48 and 0.52 cubic foot per hour the flame gives practically the same light.

407 STANDARD ELECTRICAL DICTIONARY.

Perforator.

An apparatus used in automatic high speed telegraphy for perforating strips of paper. These are then used by drawing between a roller and contact spring for making and breaking the telegraphic circuit for the production of a record, such as the Morse record, at the distant receiving station.

The perforated strip has different cla.s.ses of holes punched in it to represent dots or dashes. It is fed by machinery very rapidly, so that the message is transmitted with the highest speed. Several operators may simultaneously prepare the paper strips, and thus in conjunction with its rapid feeding in the transmitter, far surpa.s.s the time of ordinary direct transmission.

Fig. 257. PERFORATOR FOR WHEATSTONE'S AUTOMATIC TELEGRAPH.

Perforators may be entirely mechanical but are sometimes pneumatic, compressed air being used to operate them. The holes they make are on different levels of the paper strip, as shown in the cut.