A colorless crystalline substance, C4H6.(OH)4, of a
   sweet, cooling taste, extracted from certain lichens, and obtained by
   the decomposition of erythrin; -- called also erythrol, erythroglucin,
   erythromannite, pseudorcin, cobalt bloom, and under the name phycite
   obtained from the alga Protococcus vulgaris. It is a tetrabasic
   alcohol, corresponding to glycol and glycerin.