Squaric acid: Reactions with certain metals

Abstract The metals which were exposed to the action of aqueous squaric acid formed salts of comparatively low solubility. At room temperatures the solubility of magnesium squarate dihydrate, for example, was in the 0.5% range. Of the metals investigated only magnesium and zinc could be said to react rapidly. Under the conditions imposed some of the metals, such as nickel, aluminum, and indium, required many hours, or even days, to react sufficiently to yield precipitates. The activity of certain metals could be increased by placing in intimate contact with metallic copper. Predictably, only iron, cobalt, and nickel formed colored squarates. In general the salt of a given metal appeared in several different forms. Although there was some similarity in the crystalline forms of the various squarates, there was a tendency for those of several metals, such as aluminum and lead, to be restricted to smaller dimensions than others, such as zinc and cadmium. An interesting property of the product formed by tin was that the spontaneous evaporation of part of the moisture from the reaction mixture yielded a gel, in which the original crystalline forms could no longer be detected. This property was not observed in connection with any of the other metals studied.