N.Y. Gen. Bus. Law § 320

§ 320. Standard of purity. The gas furnished or supplied by any\ncorporation, association, partnership or person in any city of the\nsecond class shall be free from sulphuretted hydrogen, to be determined\nby exposing for thirty seconds a slip of white paper saturated with\nacetate of lead to a jet of gas flowing about five feet per hour, and\neach one hundred cubic feet shall not contain more than ten grains of\nammonia nor twenty grains of sulphur.\n