No salt or other corrosive chemical is permissible as a protection against freezing. (_f_) Must in general comply with the requirements governing the construction of apparatus for isolated installations so far as they are applicable. (_g_) Must be so arranged as to insure correct procedure in recharging and cleaning. (_h_) Generators of the carbide-feed type must be provided with some form of approved measuring device to enable the attendant to determine when the maximum allowable quantity of carbide has been fed into the generating chamber. In the operation of generators of this type an allowance of at least 1 gallon of clean generating water per pound of carbide should be made, and the generator should be cleaned after slaking of every full charge. Where lump carbide is used the lumps may become embedded in the residuum, if the latter is allowed to accumulate at the bottom of the generating chamber, causing overheating from slow and restricted generation, and rendering the mass more liable to form a hard deposit and bring severe stresses upon the walls of the generator by slow expansion. 26. GENERATING CHAMBERS.--(_a_) 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 into the outer air. (_b_) Must be so arranged as to guard against appreciable escape of gas to the room at any time during the introduction of the charges. (_c_) Must be so designed that the residuum will not clog or affect the operation of the machine and can conveniently be handled and removed. (_d_) Must be so arranged that during the process of cleaning and recharging the back-flow of gas from the gasholder or other generating chambers will be automatically prevented. 27. GASHOLDERS.--(_a_) Must be of sufficient capacity to contain at least 4 cubic feet of gas per 1/2-foot burner of the rating. This is to provide for the requisite lighting period without the necessity of making gas at night, allowance being made for the enlargement of burners caused by the use of cleaners. (_b_) Must be provided with suitable guides to direct the movement of the bell throughout its entire travel. 28. PRESSURE RELIEFS.--Must in all cases be provided, and must be so arranged as to prevent pressure in excess of 100-tenths (10) inches water column in the mains. 29. PRESSURES.--Gasholders must be adjusted to maintain a pressure of approximately 25-tenths (2.5) inches water column in the mains. CHAPTER V THE TREATMENT OF ACETYLENE AFTER GENERATION