[3] Though colourless itself, purpuric acid has a tendency to form red or purple-coloured salts with alkaline bases.

This characteristic led the English doctor William Hyde Wollaston (1766-1828) to suggest the name purpuric acid.

In 1818, Prout obtained lithic acid from the excrement of a boa constrictor (which largely consists of this substance) or else used urinary calculi.

Purpuric acid combines with the alkalis, alkaline earths, and metallic oxides.

Wolllaston believed that these characteristics were sufficient to distinguish it from an oxide, and to establish its character as an acid.