4. CAPACITY.--(_a_) Must be sufficient to furnish gas continuously for the maximum lighting period to all lights installed. A lighting period of at least 5 hours shall be provided for in every case. (_b_) Generators for conditions of service requiring lighting period of more than 5 hours must be of sufficient capacity to avoid recharging at night. The following ratings will usually be found advisable. (i) For dwellings, and where machines are always used intermittently, the generator must have a rated capacity equal to the total number of burners installed. (ii) For stores, opera houses, theatres, day-run factories, and similar service, the generator must have a rated capacity of from 30 to 50 per cent, in excess of the total number of burners installed. (iii) For saloons and all night or continued service, the generator must have a rated capacity of from 100 to 200 per cent. in excess of the total number of burners installed. (_c_) A small generator must never be installed to supply a large number of lights, even though it seems probable that only a few lights will be used at a time. _An overworked generator adds to the cost of producing acetylene gas_. 5. CARBIDE CHARGES.--Must be sufficient to furnish gas continuously for the maximum lighting period to all burners installed. In determining charges lump carbide must be estimated as capable of producing 4-1/2 cubic foot of gas to the pound, commercial 1/4-inch carbide 4 cubic feet of gas to the pound, and burners must be considered as requiring at least 25 per cent. more than their rated consumption of gas. 6. BURNERS.--Burners consuming one-half of a cubic foot of gas per hour are considered standard in rating generators. Those having a greater or less capacity will decrease or increase the number of burners allowable in proportion. Burners usually consume from 25 to 100 per cent. more than their rated consumption of gas, depending largely on the working pressure. The so- called 1/2-foot burner when operated at pressures of from 20- to 25- tenths inches water column (2 to 2-1/2 inches) is usually used with best economy. 7. PIPING.--(_a_) Connexions from generators to service-pipes must be made with right and left thread nipples or long thread nipples with lock nuts. All forms of unions are prohibited. (_b_) Piping must, as far as possible, be arranged so that any moisture will drain back to the generator. If low points occur of necessity in any piping, they must be drained through tees into drip cups permanently closed with screw caps or plugs. No pet-cocks shall be used. (_c_) A valve and by-pass connexion must be provided from the service-pipe to the blow-off for removing the gas from the holder in case it should be necessary to do so. (_d_) The schedule of pipe sizes for piping from generators to burners should conform to that commonly used for ordinary gas, but in no case must the feeders be smaller than three-eighths inch. The following schedule is advocated: