“…Here, Wheatstone bridge circuits in conjunction with recording potentiometers are invariably included (125, 147, 322, 347, 351, 354, 359, 362). When oxygen or excess air is the desired constituent, in an atmosphere not containing oxidizable fuels, sufficient amounts of standard fuels are added (20,23,101,179,322,363,404,495) to consume all the oxygen present, thus giving a measure of the concentration according to the heat evolved. Many commercial instruments, some of them portable, based on both principles of temperature measurement for use as safety devices in mines, fuel tanks, and tunnels, are on the market (20,58,70,319).…”