Abstract: An electrochemical device for sensing fluid components, particularly gases, comprises a composition with which the component reacts to liberate elemental chlorine, bromine, fluorine or iodine. The chlorine, bromine, fluorine or iodine passes through a particulate layer of vitreous carbon and activates the positive electrode of a solid ionic electrolyte battery of the type: halogen/solid ionic electrolyte/metal electrode, whereby a voltage is generated across a measuring device, the voltage being a known measure of the concentration of the fluid component.

Abstract: Small amounts of NO.sub.2 and O.sub.3 in air are determined by utilizing the reactions of these gases with solid alkali metal halides to produce halogen, and the reaction of NO.sub.2 with various salts such as PbI.sub.2 to produce NO; halogens produced from the reaction may be measured by the use of an electrolytic cell, the output of which is dependent on the halogen concentration of the gas contacting one electrode thereof, while the NO concentration may be determined by the chemiluminescence technique.

Abstract: Sulphur dioxide is reacted with silver nitrite at room temperature to release nitrogen dioxide in a known ratio and the nitrogen dioxide may, then, be measured as an indication of the presence and amount of sulphur dioxide.