These rules are liable to revision from time to time. The GERMAN ACETYLENE VEREIN has drawn up (December 1904) the following code of rules for the construction, erection, and manipulation of acetylene apparatus: I. _Rules for Construction._ 1. All apparatus for the generation, purification, and storage of acetylene must be constructed of sheet or cast iron. Holder tanks may be built of brick. 2. When bare, galvanised, or lead-coated sheet-iron is used, the sides of generators, purifiers, condensers, holder tanks, and (if present) washers and driers must be built with the following gauges as minima: Holder bells. All other apparatus. Up to 7 cubic feet capacity 0.75 mm. 1.00 mm. From 7 to 18 " 1.00 1.25 From 18 to 53 " 1.25 1.50 Above 53 " 1.50 2.00 When not constructed of cast-iron, the bottoms, covers, and "manhole" lids must be 0.5 mm. thicker in each respective size. In all circumstances, the thickness of the walls--especially in the case of apparatus not circular in horizontal section--must be such that alteration in shape appears impossible, unless deformation is guarded against in other ways. Generators must be so constructed that when they are being charged the carbide cannot fall into the residue which has already been gasified; and the residues must always be capable of easy, complete, and safe removal. 3. Generators, purifiers, and holders must be welded, riveted or folded at the seams; soft solder is only permissible as a tightening material. 4. Pipes delivering acetylene, or uniting the apparatus, must be cast- or wrought-iron. Unions, cocks, and valves must not be made of copper; but the use of brass and bronze is permitted. 5. When cast-iron is employed, the rules of the German Gas and Water Engineers are to be followed. 6. In generators where the whole amount of carbide introduced is not gasified at one time, it must be possible to add fresh water or carbide in safety, without interfering with the action of the apparatus. In such generators the size of the gasholder space is to be calculated according to the quantity of carbide which can be put into the generator. For every 1 kilogramme of carbide the available gasholder space must be: for the first 50 kilos., 20 litres; for the next 50 kilos., 15 litres; for amounts above 100 kilos., 10 litres per kilo. [One kilogramme may be taken as 2.2 lb., and 28 litres as 1 cubic foot.] The generator must be large enough to supply the full number of normal (10-litre) burners with gas for 5 hours; the yield of acetylene being taken at 290 litres per kilo. [4.65 cubic feet per lb.] The gasholder space of apparatus where carbide is not stored must be at least 30 litres for every normal (10-litre) flame.