Abstract: An apparatus (1) for determining the concentration of a critical first component, such as hydrogen, of an atmosphere or environment (E), wherein the first component is capable of forming a combustible mixture with a second component, such as oxygen; the apparatus comprises: (A) a sampling unit (10) including: (A1) a small measuring chamber (12) operatively connected with an ignition means (135) capable of being operated so as to initiate in said chamber a combustion of said critical first component by reaction with said second component, and (A2) at least one sensor (15) operatively connected with said measuring chamber for generating a signal formed by essentially proportionate contributions from all significant components contained in said measuring chamber; (B) at least one flame arrestor (14) intervening between said measuring chamber (12) and aid environment (E) of interest; and (C) a control unit (16) capable of imposing a mode of operation in at least two distinct phases wherein, during a first phase,

Abstract: Electroanalytic transducers for electrochemical analysis of chemical substances are disclosed. The transducers are of the type which include electrodes contacting an electrolyte solution. In accordance with the method and apparatus of the invention, means insulating an electrode are held in a mutually pressing engagement over preselected portions of the electrode to insulate that portion from the electrolyte and prevent creep of the electrolyte between the insulating means and the preselected portions. Thus, the surface area of the electrode exposed to the electrolyte is maintained substantially constant during the service life of the transducer. In a preferred embodiment, sensor or working and counter electrodes are coaxially mounted and circumferentially coaxially separated by annular insulating means. Spring means urge the inner coaxially mounted electrode and the annular insulating means together so that only the surface of the cross-sectional end of the inner electrode is exposed to electrolyte.