2006 New York Code - Standard Of Purity.

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