Minisferio da &ricullura, Rio de Janeiro (Bmzil) The majority of the chemical methods for the detection and determination of carbon monoxide are based on redox reactions of this gas with palladium and silver salts, whereby the metallic palladium or silver formed indicates both qualitatively and quantitatively the carbon monoxide present'. Other methods based on the formation of coloured metal components by the direct or indirect action of carbon monoxide have been developed recently2. One of the oldest and most widely used redox reactions is that with PdCl, which in ionic form can be written : Pd+a + CO + H,O --f Pd" + CO, + 2H+ I When the redox reaction is written as a molecular reaction with consideration of the anionic radicals (A) envolvcd, we get: PdA, + CO + H,O + Pd" + CO, + 2HA Ia PdA, + CO + H,O + Pd" + CO, + 2H-t + 2A-rb Analogous reactions are valid for redox reactions with silver salts. From xa and Ib it seems obvious that the detection of carbon monoxide should also be possible by means of the detection of the acids or their anions which are formed. Clearly this form of a CO-test requires slightly soluble palladium and silver salts capable of reacting rapidly with carbon monoxide. We can expect a higher sensitivity, if the liberated anions can be detected before the equivalent amount of metallic palladium (silver) is visible. In view of these considerations experiments were carried out with innercomplex palladium salts, i.e., Pd-dimethylglyoximate, Pd-salicylaldoximate and Pd-8hyclroxiquinolinate. If redox reactions as stated in xa and rb take place, the liberated dimethylglyoxime, salicylaldoxime, or 8-hydroxiquinoline would be