Hydrogen Cyanide (Anhydrous) by Wöhler's Method

Anhydrous hydrogen cyanide (prussic acid) is a clear liquid and a deadly poison. Crawford's 1936 patent turns it into acetone cyanohydrin, the start of acrylic glass. This is Wöhler's laboratory method as the 1907 US Dispensatory gives it: fuse potassium ferrocyanide to a black cyanide, set the acid free with diluted sulphuric acid, dry the vapour over calcium chloride and distil it into an ice-cold bottle. The source gives no strength for the acid: none is given here. The picture: pure liquid hydrogen cyanide in a glass ampoule (Pok, Wikimedia Commons, CC BY-SA 4.0).