An inorganic compound, this yellow hygroscopic solid is used to form tetra-, hexa-, and decahydrates. Sodium chromate is primarily used as an intermediate in the extraction process of chromium from raw ore. As with other hexavalent chromium compounds, sodium chromate is toxic and carcinogenic. In term of production, sodium chromate is produced on a mass scale by heating chromium ores in areas with separate quantities of sodium carbonate. This roasting process is what makes chromium ater extractable, leaving iron oxides behind as a byproduct. Calcium carbonate (slaked lime) is often added to the mixture to increase oxygen access and minimize any silicon or aluminium impurities that may be present. In addition to its integral role in chromium refining, sodium chromate is also used to inhibit corrosion in the petroleum industry, and to preserve wood. In the pharmaceutical industry, it is a diagnostic used to determine the volume of red blood cells.