Sodium tungstate dihydrate

In patch testing this chemical is used to diagnose a contact allergy to tungsten. Tungsten, also known as wolfram, is a metal. It can be found in incandescent light bulb filaments, X-ray tubes, and electrodes in welding, superalloys, and radiation shielding. About half is used in the form of tungsten carbide, WC. Tungsten's hardness and high density give it military applications in penetrating projectiles. Tungsten compounds are also often used as industrial catalysts.
Tungsten is the only metal from the third transition series that is known to occur in biomolecules, where it is used in a few species of bacteria and archaea. In medicine, tungsten can be found in medical devices such as joint replacements, intravascular devices and dental implants. Tungsten is also used in jewelry.