(_f_) The apparatus must be capable of withstanding fire from outside causes. Sheet-metal joints must be double-seamed or riveted and thoroughly sweated with solder. Pipes must be attached to sheet-metal with lock-nuts or riveted flanges. This prohibits the use of wood or of joints relying entirely upon solder. (_g_) Gauge glasses, the breakage of which would allow the escape of gas, must not be used. (_h_) The use of mercury seals is prohibited. Mercury has been found unreliable as a seal in acetylene apparatus.(_i_) Combustible oils must not be used in connexion with the apparatus. (_j_) The construction must be such that liquid seals shall not become thickened by the deposit of lime or other foreign matter. (_k_) The apparatus must be constructed so that accidental siphoning of water will be impossible. (_l_) Flexible tubing, swing joints, unions, springs, mechanical check-valves, chains, pulleys, stuffing-boxes and lead or fusible piping must not be used on acetylene apparatus except where failure of such parts will not vitally affect the working or safety of the machine. Floats must not be used excepting in cases where failure will result only in rendering the machine inoperative. (_m_) Every machine must be plainly marked with the maximum number of lights it is designed to supply, the amount of carbide necessary for a single charge, the manufacturer's name and the name of the machine. 16. GENERATING CHAMBERS.--(_a_) Must be constructed of galvanised iron or steel not less than No. 24 U.S. Standard gauge in thickness for capacities up to and including 20 gallons, not less than No. 22 U.S. Standard gauge for capacities between 20 and 75 gallons, and not less than No. 20 U.S. Standard gauge for capacities in excess of 75 gallons. (_b_) Must each be connected with the gasholder in such a manner that they will, at all times, give open connexion either to the gasholder or to the blow-off pipe to the outer air. This prevents dangerous pressure within or the escape of gas from the generating chamber. (_c_) Must be so constructed that not more than 5 pounds of carbide can be acted upon at once, in machines which apply water in small quantities to the carbide. This tends to reduce the danger of overheating and excessive after- generation by providing for division of the carbide charges in machines of this type. (_d_) Must be provided with covers having secure fastenings to hold them properly in place and those relying on a water-seal must be submerged in at least 12 inches of water. Water-seal chambers for covers depending on a water-seal must be 1-1/2 inches wide and 15 inches deep, excepting those depending upon the filling of the seal chambers for the generation of gas, where 9 inches will be sufficient. (_e_) Must be so designed that the residuum will not clog or affect the working of the machine and can conveniently be handled and removed.