Most often in connection with Alchemy. Vitriol was the most important liquid in alchemy. It was the one in which all other reactions took place. Physically the Green Lion was usually a name for vitriol, or the sulphuric acid created by distilling the green crystals of iron sulphate in a flask. Iron sulphate was formed when iron ores rich in sulphides were left to oxidise in the air, so was readily available to medieval alchemists. The sharp penetrating sulphuric acid could create major chemical changes in many materials even to the extent of dissolving metals like iron, and copper. This Green Vitriol is symbolized by the Green Lion in drawings. After the Green Vitriol (copper sulfate) was collected, it was heated and broken down into iron compounds and sulfuric acid. The acid was separated out by distillation. The first distillation produced a brown liquid that stunk like rotten eggs, but further distillation yielded a nearly odorless, yellow oil called simply Vitriol. The acid readily dissolves human tissue and is severely corrosive to most metals, although it has no effect on gold. White Vitriol is zinc sulfate; Blue Vitriol is copper sulfate.
The Green Lion could also be the nitric acid formed from heating saltpeter or nitre and iron sulphate. Nitric acid when mixed with the acid derived from common salt, hydrochloric acid, produced aqua regia, a greenish tinged liquid that could dissolve even the noble metal gold. The Green Lion devouring the sun is a famous image in alchemy being depicted in many manuscripts and engravings, and can be thought of as aqua regia dissolving the solar gold and forming a solution which could readily tinge metals with gold.
