An ingenious electric regulator, which is so simple that any amateur can construct it, and that, too, at little eipense, has keen devised by C. Pollak. A few small pieces of wood, some brass, and 4 wires, are nil that is necessary for the comtruction of a regulator which will openite in a very satisfactory manner. In addition to its great simplicity, this lamp has the advantage of being- bused upon an entirely new principle - that of the expansion of the wires that lead the current to the carbons under the influence of the said current and its variations, the same part serving at the same time for the lighting or formation of the arc, and for regulation in measure as the carbons wear away.
Fig. 130 shows the first of these apparatus that, ivus constructed, and will easily allow the operation to be understood. Along a board /, about 6 ft. long, are stretched 2 brass wires a a', 1/60 in. diameter. These nre fixed at the upper part to the 2 terminals of the lamp, and kept taut below by the action of double spiral springs 6 6'. These latter are formed of simple brass wire, and are fixed at the side of the board, and form in the centre a lateral appendage, to which N soldered the corresponding wire. At the other extremity they arc prolonged by a straight portion d, and a spiral forming a carbon holder.
In order that the carbons may be always kept opposite each other, the displacement of the holders is guided by a bant wire c c' affixed to the board. The length of the lever arm d is about 4 in., while the distance from thepoint of attachment of the wires a to the centre of the spring is 9/16 in., so that the motions are amplified at the ratios of 1 to 5. In a normal state, the distance of the carbon holders is about l\ in. When the carbons are put, in, each is made to project 1 3/4 in., so that the holders have to be spaced 2 1/2 in. apart, corresponding to an elongation of about 1/4 in. of the wires a a'. If, at this moment, the lamp be interposed in an electric circuit, the current will pass into these wires and eat them, and the springs being thereby bent back the carbons will tend to separate, and an arc will form. The length of the latter will be determined by the condition that the tensions of the springs and wires balance each other for the corresponding strength of the current; for, as the regulation is made in series, and bears on the cm-rent, we ought naturally to group these lamps in derivation.
In measure as the carbons wear away, the resistance of the arc increases, the current diminishes, and the wires contract, allowing the springs to carry buck the carbons. It is easy to see, and experiment shows it, that the current tends to diminish slowly in measure as the lamp burns. Such gradual diminution in luminous intensity offers scarcely any inconvenience in a lamp of this kind. With the divisions indicated the lamp will operate for about 3 hours.
The diameter of 1/50 in. for the regulating wires is determined by the value of the current adopted, 5 amperes; and the condition that the temperature of the wire be relatively high, about 120° 0. If the temperature is too low, the regulation will be effected too slowly; and if it is too high, the elasticity of the wire will be destroyed, and the latter will elongate permanently under the action of its spring.
The temperature of 120° C. has been calculated by means of the well-known formula where t is the elevation of temperature, K the specific resistance, i the current, h the coefficient of regulation (0*0002), d the diameter of the wire, and J the mechanical equivalent of heat.
The length does not here figure explicitly,butit in fact determines the current. In order to keep the latter constant by diminishing the length, it is necessary to increase by so much the proportion of amplification of the levers, and this has been done in a later model of smaller dimensions. If, with the same temperature, we desire to modify tins current, it will suffice to shunt the regulating wires by properly calculated auxiliary resistances.
The ambient temperature plays an important role, since it modifies the initial tension of the wires. To get free from this influence, which in certain cases would necessitate a different regulation for each temperature, it suffices to replace the wood by a frame of the same metal as the wires a. Pollak has likewise adapted his system to lamps regulatable in derivation, with vertical carbons, by making the regulating wire act upon a ring brake that allows the upper carbon to slide. - (La Lumiere Electrique).
Get 2 half-round porous cups and a round glass jar large enough for the 2 porous cups to stand in upright, Get 2 plates of sheet lead 1/16 in. thick, wide enough to fit the half-round side of the porous cups and deep enough to come an inch or so above the top edge of the cups and jar. Solder a stout copper wire or a screw post to each lead plate at the top. Place the lead plates in the cups, and fill the cups nearly full with a paste made of red lead mixed with a solution of sulphate of soda thin enough to run like a cement. The glass jar containing the cups should be filled to within 1/2 in. of top of cups with sulphuric acid and water, about 1 part acid and 8 of water. One plate should be marked X, so that, in charging, the currents will be correctly connected. This may be charged by attaching to a series of 12 sulphate of copper cells for 24 hours, or from a dynamo. It should always be charged in same direction, and it will improve by repeated charg-ings. A wooden cover may be fitted to the glass jar, and evaporation of the fluid should be replenished by adding water. Two or more cells of this battery will work small motors, lamps, and induction coils, and if thoroughly charged will retain a large volume of electricity for considerable time.