Barium sulfide

Barium sulfide is the inorganic compound with the formula BaS. BaS is the barium compound produced on the largest scale. It is an important precursor to other barium compounds including BaCO3 and the pigment lithopone, ZnS/BaSO4. Like other chalcogenides of the alkaline earth metals, BaS is a short wavelength emitter for electronic displays. It is colorless, although like many sulfides, it is commonly obtained in impure colored forms.

Discovery
BaS was prepared by the Italian alchemist Vincenzo Cascariolo (also known as Vincentius or Vincentinus Casciarolus or Casciorolus, 1571–1624) via the thermo-chemical reduction of BaSO4 (available as the mineral barite). It is currently manufactured by an improved version of Cascariolo's process using coke in place of flour and charcoal. This kind of conversion is called a carbothermic reaction:


 * BaSO4 + 2C  →  BaS  +  2CO2

and also:
 * BaSO4 + 4C  →  BaS  +  4CO

The basic method remains in use today. BaS dissolves in water. These aqueous solutions, when treated with sodium carbonate or carbon dioxide, give a white solid of barium carbonate, a source material for many commercial barium compounds.

According to Harvey (1957), in 1603, Vincenzo Cascariolo used barite, found at the bottom of Mount Paterno near Bologna, in one of his non-fruitful attempts to produce gold. After grinding and heating the mineral with charcoal under reducing conditions, he obtained a persistent luminescent material rapidly called Lapis Boloniensis, or Bolognian stone. The phosphorescence of the material obtained by Casciarolo made it a curiosity.

Preparation
A modern procedure proceeds from barium carbonate:
 * BaCO3 + H2S  ->  BaS  +  H2O  +  CO2

BaS crystallizes with the NaCl structure, featuring octahedral Ba2+ and S2− centres.

The observed melting point of barium sulfide is highly sensitive to impurities.

Safety
BaS is quite poisonous, as are related sulfides, such as CaS, which evolve toxic hydrogen sulfide upon contact with water.