In many places it is desirable to sell gas in small quantities and to prepay the amount for a given supply of gas. This is accomplished by a meter such as that of Fig. 179. The meter is constructed much the same as the former but provided with a mechanism such that when a coin - usually 25 cents - is deposited, according to the printed directions in the instrument, an amount of gas representing the proportional current rate is allowed to pass the meter. The supply is cut off as soon as the amount paid for is used; when in order to receive more gas, another coin must be deposited as before. Gas-service Rules. - The rules for the regulation of gas service are in many States under the control of a board or commission whose duty it is to form codes prescribing the measurement and sale of all public utilities. The following form, General Order No. 20, State Public Utilities Commission of Illinois, gives an idea of the requirements in that State for the sale of coal gas.

Fig. 179. - The prepayment gas meter.

Rule 3. Request Tests. - Each utility furnishing metered service shall make a test of the accuracy of any meter, upon written request by a consumer: Provided, first, that the meter in question has not been tested by the utility or by the commission within 6 months previous to such request; and second, that the consumer will agree to accept the result of the test made by the utility as determining the basis for settling the difference claimed. No charge shall be made to the consumer for any such test. A report, giving the result of every such test, shall be made to the consumer.

Rule 4. Adjustment of Bills for Meter Error. - If on any test of a service meter, either by the utility or by the commission, such meter shall be found to have a percentage of error greater than that allowed in Rule 11 (see below) for gas meters, the following provisions for the adjustment of bills shall be observed.

(A) Fast Meters

If the meter is faster than allowable, the utility shall refund to the consumer a percentage of the amount of his bills for the 6 months previous to the test or for the time the meter was installed, not exceeding 6 months, corresponding to the percentage of error of the meter. No part of a minimum, service or demand charge need be refunded.

(B) Slow Meters

If the meter is found not to register or to run slow, the utility may render a bill to the consumer for the estimated consumption during the preceding 6 months, not covered by bills previously rendered, but such action shall be taken only in cases of substantial importance where the utility is not at fault for allowing the incorrect meter to be in service.

Rule 11. Gas-meter Accuracy. - (a) Method of Testing. - All tests to determine the accuracy of registration of a gas service meter shall be made with a suitable meter prover. At least two test runs shall be made on each meter, the results of which shall agree with each other within one-half per cent. (1/2 %) -

(C) Allowable Error

Whenever a meter is tested to determine the accuracy with which it has been registering in service, it may be considered as correct if found not more than two per cent. (2%) in error, and no adjustment of charges shall be entailed unless the error is greater than this amount.

Rule 15. Heating Value. - Each utility furnishing manufactured gas shall supply gas which at any point at least 1 mile from the plant, and tested in the place where it is consumed, shall have a monthly average total heating value of not less than 565 B.t.u. per cubic foot, and at no time shall the total heating value of the gas at such point be less than 530 B.t.u. per cubic foot.

To arrive at the monthly average total heating value, the results of all tests made on any one day shall be averaged and the average of all such daily averages shall be taken as the monthly average.

Rule 8. Railroad Commission of Wisconsin. - Each utility furnishing gas service must supply gas giving a monthly average of not less than 600 B.t.u. total heating value per cubic foot, as referred to standard conditions of temperature and pressure. The minimum heating value shall never fall below 550. The tests to determine the heating value of the gas shall be made anywhere within a 1-mile radius of the center of distribution.