The behaviour of the following reagents towards monovalent copper has been studied: 2.2'-dipyridyl, o-phenanthrolinc, 6.6'-dimothyl-2.2'-dipyridyl, a-pyridyl-2'-quinolyl.3'- methyl-pyridyl-2'-quinolyl. 2.2'-diquinolyl, 3'-methyl-2.2'-diquinolyl, 2-quinolyl-2'isoquinolyl. All these reagents give strongly coloured complexes with monovalent copper in alcoholic medium, the intensity of the colour varying