This white soluble crystalline substance is a highly toxic mercury salt of nitric acid originally used in the fur industry for a process known as “carroting” to felt fur for hat blocking. However, excessive exposure to the toxic material was known to cause severe psychological illness, coining the phrase “mad as a hatter.” Use of mercury nitrate di-hydrate for felting was banned in the US in 1941, and is instead used in the manufacture of trigger mechanisms for detonators used in aerial bombs and other explosives. Production of mercurous nitrate di-hydrate is relatively simple, involving a reaction of hot nitric acid with mercury to oxidize it. Other than mercury triggers for explosive detonators, mercurous nitrate dihydrate is used in mercurious reactions involving ketones such acetone. Proper universal precautions should be observed when handling and storing mercurous nitrate dihydrate, due both to its toxicity and its generation of oxygen gas as a result of its decomposition, making it a fire hazard.