Edison, His Life and Inventions [168]
amount of current passing. By reason, however, of dissatisfaction caused from the inability of customers to read the indications of the meter, it has in later years, to a great extent, been replaced by registering meters that can be read by the customer."
The principle employed in the Edison electrolytic meter is that which exemplifies the power of electricity to decompose a chemical substance. In other words it is a deposition bath, consisting of a glass cell in which two plates of chemically pure zinc are dipped in a solution of zinc sulphate. When the lights or motors in the circuit are turned on, and a certain definite small portion of the current is diverted to flow through the meter, from the positive plate to the negative plate, the latter increases in weight by receiving a deposit of metallic zinc; the positive plate meantime losing in weight by the metal thus carried away from it. This difference in weight is a very exact measure of the quantity of electricity, or number of ampere-hours, that have, so to speak, passed through the cell, and hence of the whole consumption in the circuit. The amount thus due from the customer is ascertained by removing the cell, washing and drying the plates, and weighing them in a chemical balance. Associated with this simple form of apparatus were various ingenious details and refinements to secure regularity of operation, freedom from inaccuracy, and immunity from such tampering as would permit theft of current or damage. As the freezing of the zinc sulphate solution in cold weather would check its operation, Edison introduced, for example, into the meter an incandescent lamp and a thermostat so arranged that when the temperature fell to a certain point, or rose above another point, it was cut in or out; and in this manner the meter could be kept from freezing. The standard Edison meter practice was to remove the cells once a month to the meter-room of the central-station company for examination, another set being substituted. The meter was cheap to manufacture and install, and not at all liable to get out of order.
In December, 1888, Mr. W. J. Jenks read an interesting paper before the American Institute of Electrical Engineers on the six years of practical experience had up to that time with the meter, then more generally in use than any other. It appears from the paper that twenty-three Edison stations were then equipped with 5187 meters, which were relied upon for billing the monthly current consumption of 87,856 lamps and 350 motors of 1000 horse-power total. This represented about 75 per cent. of the entire lamp capacity of the stations. There was an average cost per lamp for meter operation of twenty- two cents a year, and each meter took care of an average of seventeen lamps. It is worthy of note, as to the promptness with which the Edison stations became paying properties, that four of the metered stations were earning upward of 15 per cent. on their capital stock; three others between 8 and 10 per cent.; eight between 5 and 8 per cent.; the others having been in operation too short a time to show definite results, although they also went quickly to a dividend basis. Reports made in the discussion at the meeting by engineers showed the simplicity and success of the meter. Mr. C. L. Edgar, of the Boston Edison system, stated that he had 800 of the meters in service cared for by two men and three boys, the latter employed in collecting the meter cells; the total cost being perhaps $2500 a year. Mr. J. W. Lieb wrote from Milan, Italy, that he had in use on the Edison system there 360 meters ranging from 350 ampere- hours per month up to 30,000.
In this connection it should be mentioned that the Association of Edison Illuminating Companies in the same year adopted resolutions unanimously to the effect that the Edison meter was accurate, and that its use was not expensive for stations above one thousand lights; and that the best financial results were invariably secured in a station selling current by meter. Before the same association, at its meeting in September,
The principle employed in the Edison electrolytic meter is that which exemplifies the power of electricity to decompose a chemical substance. In other words it is a deposition bath, consisting of a glass cell in which two plates of chemically pure zinc are dipped in a solution of zinc sulphate. When the lights or motors in the circuit are turned on, and a certain definite small portion of the current is diverted to flow through the meter, from the positive plate to the negative plate, the latter increases in weight by receiving a deposit of metallic zinc; the positive plate meantime losing in weight by the metal thus carried away from it. This difference in weight is a very exact measure of the quantity of electricity, or number of ampere-hours, that have, so to speak, passed through the cell, and hence of the whole consumption in the circuit. The amount thus due from the customer is ascertained by removing the cell, washing and drying the plates, and weighing them in a chemical balance. Associated with this simple form of apparatus were various ingenious details and refinements to secure regularity of operation, freedom from inaccuracy, and immunity from such tampering as would permit theft of current or damage. As the freezing of the zinc sulphate solution in cold weather would check its operation, Edison introduced, for example, into the meter an incandescent lamp and a thermostat so arranged that when the temperature fell to a certain point, or rose above another point, it was cut in or out; and in this manner the meter could be kept from freezing. The standard Edison meter practice was to remove the cells once a month to the meter-room of the central-station company for examination, another set being substituted. The meter was cheap to manufacture and install, and not at all liable to get out of order.
In December, 1888, Mr. W. J. Jenks read an interesting paper before the American Institute of Electrical Engineers on the six years of practical experience had up to that time with the meter, then more generally in use than any other. It appears from the paper that twenty-three Edison stations were then equipped with 5187 meters, which were relied upon for billing the monthly current consumption of 87,856 lamps and 350 motors of 1000 horse-power total. This represented about 75 per cent. of the entire lamp capacity of the stations. There was an average cost per lamp for meter operation of twenty- two cents a year, and each meter took care of an average of seventeen lamps. It is worthy of note, as to the promptness with which the Edison stations became paying properties, that four of the metered stations were earning upward of 15 per cent. on their capital stock; three others between 8 and 10 per cent.; eight between 5 and 8 per cent.; the others having been in operation too short a time to show definite results, although they also went quickly to a dividend basis. Reports made in the discussion at the meeting by engineers showed the simplicity and success of the meter. Mr. C. L. Edgar, of the Boston Edison system, stated that he had 800 of the meters in service cared for by two men and three boys, the latter employed in collecting the meter cells; the total cost being perhaps $2500 a year. Mr. J. W. Lieb wrote from Milan, Italy, that he had in use on the Edison system there 360 meters ranging from 350 ampere- hours per month up to 30,000.
In this connection it should be mentioned that the Association of Edison Illuminating Companies in the same year adopted resolutions unanimously to the effect that the Edison meter was accurate, and that its use was not expensive for stations above one thousand lights; and that the best financial results were invariably secured in a station selling current by meter. Before the same association, at its meeting in September,