Physico-chemical mechanism of the argyrophil I reaction.

Kinetic experiments have shown that the argyrophil I reaction (the formation of metallic from ionic silver by reducing groups of the tissues) is a catalytic process. Topochemical considerations, and several reaction kinetic observations, suggest that the semi-conductor properties and the favourable chemical structure of certain sites (catalytic points) of the tissue structure play a fundamental role in the catalysis. The electrochemical half processes in the argyrophil I reaction (i.e., the transformation of tissue-bound reducing groups into their oxidized form and the reduction of silver ions into silver atoms) take place separately in space, while the electrons released in the former half reaction are transported by the semi-conduction bands of the tissue to the catalytic points where the metallic silver grains are formed.