(Rule 14, referring to the storage of carbide, has been quoted in Chapter II. (page 19)). RULES FOR THE CONSTRUCTION OF GENERATORS. The following Rules are intended to provide only against the more hazardous defects usually noted in apparatus of this kind. The Rules do not cover all details of construction nor the proper proportioning of parts, and devices which comply with these requirements alone are not necessarily suitable for listing as permissible for use. These points are often only developed in the examination required before permission is given for installation. _Class A.--Stationary Apparatus for Isolated Installations._ 15. GENERAL RULES. GENERATORS.--(_a_) Must be made of iron or steel, and in a manner and of material to insure stability and durability. (_b_) Must be automatically regulated and uniform in their action, producing gas only as immediate consumption demands, and so designed that gas is generated without producing sufficient heat to cause yellow discoloration of residuum (which will occur at about 500° F.) or abnormal pressure at any stage of the process when using carbide of any degree of fineness. The presence of excessive heat tends to change the chemical character of the gas and may even cause its ignition, while in machines of the carbide-feed type, finely divided carbide will produce excessive pressure unless provision is made to guard against it. (_c_) Must be so arranged that during recharging, back flow of gas from the gasholder will be automatically prevented, or so arranged that it will be impossible to charge the apparatus without first closing the supply-pipe to the gasholder, and to the other generating chambers if several are used. This is intended to prevent the dangerous escape of gas. (_d_) The water or carbide supply to the generating chamber must be so arranged that gas will be generated long enough in advance of the exhaustion of the supply already in the gasholder to allow the using of all lights without exhausting such supply. This provides for the continuous working of the apparatus under all conditions of water-feed and carbide charge, and it obviates the extinction of lights through intermittent action of the machine. (_e_) No valves or pet-cocks opening into the room from the gas- holding part or parts, the draining of which will allow an escape of gas, are permitted, and condensation from all parts of the apparatus must be automatically removed without the use of valves or mechanical working parts. Such valves and pet-cocks are not essential; their presence increases the possibility of leakage. The automatic removal of condensation from the apparatus is essential to the safe working of the machine. U-traps opening into the room from the gas-holding parts must not be used for removal of condensation. All sealed drip connexions must be so arranged as to discharge gas to the blow-off when blown out, and the seals must be self-restoring upon relief of abnormal pressure.