17. The Association strongly advise the use of an efficient purifier with generating plant for indoor lighting. 18. No composition piping shall be used in any part of a permanent installation. 19. Before being covered in, all pipe-work (main and branches) shall be tested in the following manner: A special acetylene generator, giving a pressure of at least 10 inches water column in a gauge fixed on the furthest point from the generator, shall be connected to the pipe-work. All points shall be opened until gas reaches them, when they shall be plugged and the main cock on the permanent generator turned off, but all intermediate main cocks shall be open in order to test underground main and all connexions. The gauge must not show a loss after generator has been turned off for at least two hours. 20. After the fittings (pendants, brackets, &c.) have been fixed and all burners lighted, the gas shall be turned off at the burners and the whole installation shall be re-tested, but a pressure of 5 inches shall be deemed sufficient, which shall not drop lower than to 4-1/2 inches on the gauge during one hour's test. 21. No repairs to, or alterations in, any part of a generator, purifier, or other vessel which has contained acetylene shall be commenced, nor, except for recharging, shall any such part or vessel be cleaned out until it has been completely filled with water, so as to expel any acetylene or mixture of acetylene and air which may remain in the vessel, and may cause a risk of explosion. _Recommendation_.--It being the general practice to store carbide in the generator-house, the Association recommend that the carbide shall be placed on a slightly raised platform above the floor level. THE BRITISH FIRE OFFICES COMMITTEE in the latest revision, dated July 15, 1907, of its Rules and Regulations _re_ artificial lighting on insured premises, includes the following stipulations applicable to acetylene: Any apparatus, except as below, for generating, purifying, enriching, compressing or storing gas, must be either in the open or in a building used for such purposes only, not communicating directly with any building otherwise occupied. An acetylene portable apparatus is allowed, provided it holds a charge of not more than 2 lb. of carbide. A cylinder containing not more than 20 cubic feet of acetylene compressed and (or) dissolved in accordance with an Order of Secretary of State under the Explosives Act, 1875, is allowed. The use of portable acetylene lamps containing charges of carbide exceeding the limit of 2 lb. allowed under these Rules (the average charge being about 18 lb.) is allowed in the open or in buildings in course of erection. Liquid acetylene must not be used or stored on the premises. The pipe, whether flexible or not, connecting an incandescent gas lamp to the gas-supply must be of metal with metal connexions. (The reference in these Rules to the storage of carbide has been quoted in Chapter II. (page 19).)