ferrocyanic : Idioms & Phrases

• noun a white unstable acid formed from ferrocyanide salts
  

WordNet

• (Chem.), a white crystalline substance, H4(CN)6Fe, of strong acid properties, obtained from potassium ferrocyanide, and regarded as the type of the ferrocyanides; called also hydro-ferrocyanic acid, hydrogen ferrocyanide. etc.

Webster 1913