1911 Encyclopædia Britannica/Erythrite

ERYTHRITE, the name given to (1) a mineral composed of a hydrated cobalt arsenate, and (2) in chemistry, a tetrahydric alcohol. (1) The mineral erythrite has the formula Co₃(AsO₄)₂·8H₂O, and crystallizes in the monoclinic system and is isomorphous with vivianite. It sometimes occurs as beautiful radially-arranged groups of blade-shaped crystals with a bright crimson colour and brilliant lustre. On exposure to light the colour and lustre deteriorate. There is a perfect cleavage parallel to the plane of symmetry, on which the lustre is pearly. Cleavage flakes are soft (H = 2), sectile and flexible; specific gravity 2.95. The mineral is, however, more often found as an earthy encrustation with a peach-blossom colour, and in this form was early (1727) known as cobalt-bloom (Ger. Kobaltblüthe). The name erythrite, from ἐρυθρός, “red,” was given by F. S. Beudant in 1832. Erythrite occurs as a product of alteration of smaltite (CoAs₂) and other cobaltiferous arsenides. The finest crystallized specimens are from Schneeberg in Saxony. The earthy variety has been found in Thuringia and Cornwall and some other places. (2) The alcohol erythrite has the constitutional formula HO·H₂C·CH(OH)·CH(OH)·CH₂OH; it is also known as erythrol, erythroglucin and phycite. It corresponds to tartaric acid, and, like this substance, it occurs in four stereo-isomeric forms. The internally compensated modification, i-erythrite, corresponding to mesotartaric acid, occurs free in the algae Protococcus vulgaris, and as the orsellinate, erythrin, C₄H₆(OH)₂(O·C₈H₇O₃)₂, in many lichens and algae, especially Roccella montagnei. It has a sweet taste, melts at 126°, and boils at 330°. Careful oxidation with dilute nitric acid gives erythrose or tetrose, which is probably a mixture of a trioxyaldehyde and trioxyketone. Energetic oxidation gives erythritic acid and mesotartaric acid. i-Erythrite and the racemic mixture of the dextro and laevo varieties were synthesized by Griner in 1893 from divinyl.