Pregled posta

Marketing

As the producer and the consumer of electricity are generally different people, it is necessary to have some method of measuring the electricity consumed in order to have it valued, as with gas. According to Ohm's law, the current increases in a closed circuit with the electromotive force, and it decreases as the resistance increases. Edison, by using a shunt system, secured that the resistance in the circuit will be the larger the fewer lamps are inserted in the circuit. In Edison's system, therefore, we have a resistance inversely proportional to current, and also inversely proportional to the number of lamps inserted. But the amount of the separated products of decomposition in a voltameter is proportional to the current; it follows, therefore, that the amount of these products of decomposition must be proportional to the number of lamps burning. It must, therefore, be a measure of the amount of electricity consumed by the lamps. On this principle Edison constructed several kinds of apparatus, one of which is represented in Fig. 342. Two voltameters z z1 are placed in an iron case, and each of them has two zinc plates p and p1 insulated by means of gutta-percha, and immersed in a solution of zinc sulphate. The current decomposes the solution, separating zinc at the negative electrode and sulphuric acid at the positive electrode. The sulphuric acid separated out at the latter dissolves the zinc of the plate. Hence, while the current flows the positive plate becomes continually lighter, and the negative heavier. The effect of the electric current then is a transference of the positive to the negative plate. If the voltameter were to be inserted directly into the circuit, one of the zinc plates would be very soon dissolved: to prevent this Edison inserts resistances w2 and w3 consisting of German silver shunts, so that only a branch current enters the voltameter. The resistance w2 is double the resistance w3 therefore the separated quantity of zinc in one of the voltameters is four times as large as in the other. The one is intended for the monthly measurements, the other serves as check to the former. To render the process of decomposition independent of temperature, two resistance wires w and wl are inserted; so that when the temperature rises the resistance in the wire will be increased, but that in the liquid diminished. By giving a suitable resistance to the wire, the changes of resistance in the wire and liquid may be made to balance each other.
The spring f consists of two different metals, and serves the purpose of causing the contact pins c and q to touch whenever the temperature has been lowered beyond a certain limit, and by this means to insert the lamp /into the circuit. As soon as the desired temperature in the fluids of the voltameter is again obtained, the springs bend upwards, and contact with the lamp is broken.
The apparatus just described is made in two sizes, one for twenty-five and the other for fifty lamps.

Sterling silver, guage 18, lid with plique a jour knob, base set with six enamel paillions, and mounted on rosewood platform. Overall measurements approx. 7 1/2" D x 7" H.
Note: This piece was designed and handmade by Vincent Ferrini to satisfy the "masterpiece" requirement for the MFA degree awarded by Rochester Institute of Technology, School for American Craftsmen. As was policy with RIT, all needed material was provided to the graduate student by RIT. These "masterpieces" were then kept by RIT for a period of ten years for use in displays, to augment the fine reputation of RIT graduate work. After the ten-year period, the policy was that a masterpiece could be bought back from RIT for the current value of materials used. Ferrini contacted RIT intending to buy back his "master-piece", only to be informed that the piece could not be found. Ferrini was, of course, astounded. No one there at RIT would offer any kind of explanation. This is the only known photo of the piece and the mystery was never solved. Perhaps a collector, somewhere, might know of its whereabouts.