(1) The purifying material shall remove phosphorus and sulphur compounds to a commercially satisfactory degree; _i.e._, not to a greater degree than will allow easy detection of escaping gas through its odour. (2) The purifying material shall not yield any products capable of corroding the gas-mains or fittings. (3) The purifying material shall, if possible, be efficient as a drying agent, but the Association does not consider this an absolute necessity. (4) The purifying material shall not, under working conditions, be capable of forming explosive compounds or mixtures. It is understood, naturally, that this condition does not apply to the unavoidable mixture of acetylene and air formed when recharging the purifier. (5) The apparatus containing the purifying material shall be simple in construction, and capable of being recharged by an inexperienced person without trouble. It shall be so designed as to bring the gas into proper contact with the material. (6) The containers in purifiers shall be made of such materials as are not dangerously affected by the respective purifying materials used. (7) No purifier shall be sold without a card of instructions suitable or hanging up in some convenient place. Such instructions shall be of the most detailed nature, and shall not presuppose any expert knowledge whatever on the part of the operator. Reference also to the abstracts of the official regulations as to acetylene installations in foreign countries given in Chapter IV. will show that they contain brief rules as to purifiers.