Other Early Stations--The Meter - 5

Other Early Stations--The Meter - 5

 Here again Edison laid the foundation of standard practice. It is true that even down to

the present time the flat rate is applied to a great deal of incandescent lighting, each lamp

being charged for individually according to its probable consumption during each month.

This may answer, perhaps, in a small place where the manager can gauge pretty closely

from actual observation what each customer does; but even then there are elements of

risk and waste; and obviously in a large city such a method would soon be likely to result

in financial disaster to the plant. Edison held that the electricity sold must be measured

just like gas or water, and he proceeded to develop a meter. There was infinite scepticism

around him on the subject, and while other inventors were also giving the subject their

thought, the public took it for granted that anything so utterly intangible as electricity,

that could not be seen or weighed, and only gave secondary evidence of itself at the exact

point of use, could not be brought to accurate regis- tration. The general attitude of doubt

was exemplified by the incident in Mr. J. P. Morgan's office, noted in the last chapter.

Edison, however, had satisfied himself that there were various ways of accomplishing the

task, and had determined that the current should be measured on the premises of every

consumer. His electrolytic meter was very successful, and was of widespread use in

America and in Europe until the perfection of mechanical meters by Elihu Thomson and

others brought that type into general acceptance. Hence the Edison electrolytic meter is

no longer used, despite its excellent qualities. Houston & Kennelly in their Electricity in

Everyday Life sum the matter up as follows: "The Edison chemical meter is capable of

giving fair measurements of the 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it has in later years, to a great extent, been replaced by registering meters that can be read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.