Ammonium thiocyanate, conversion thiocyanic acid

HCN is not completely stable and is marketed as a stabilized (often with H3PO4), flammable, anhydrous material. It reacts when heated, or in the presence of base or water, and may polymerize violently in contact with strong acids (e.g., sulfuric acid). Polymerization, once initiated, can be autocatalytic and, under confined conditions, lead to an explosion. It can be removed from waste streams by conversion to ammonium thiocyanate, a process involving scmbbing the waste stream with elemental sulfur in water (http //www.chemalliance.org). 

Barium thiocyanate was first prepared by Berzelius, who roasted barium hexacyanoferrate(II) with sulfur. It has also been obtained by reaction of barium carbonate with a solution of thiocyanic acid, by conversion of ammonium thiocyanate through the copper (I) thiocyanate by consecutive reactions with copper(I) chloride and barium hydroxide, by treatment of Prussian blue with barium sulfide, and by reaction of barium sulfide, sulfur, and cyanamide. The procedure described below makes possible the preparation of barium thiocyanate in any desired quantity from barium hydroxide and ammonium thiocyanate as starting materials. The 3-hydrate, " which is obtained first, is dehydrated readily to yield anhydrous barium thiocyanate. 

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