Preparation of Hydroxylamine hydrochloride

40g potassium nitrite (KNO2) and 50g potassium acetate (CH3COOK) are dissolved in 100ml ice water. 750g finely crushed ice is added. Into this solution a stream of sulfur dioxide (SO2) is bubbled until the solution smells of SO2. The temperature must be kept below 0°C through the whole reaction. The salt of K2[HON(SO3)2] separates and is filtered off and washed with ice water. The salt is dissolved in 500ml 0.5 M HCl and boiled for two hours. Still boiling a solution of Barium chloride (BaCl2) is added as long as barium sulfate (BaSO4) precipitates (maybe CaCl2 will do instead). The BaSO4 is filtered off and the clear filtrate is evaporated to dryness. The residue consists of Potassium Chloride (KCl) and NH2OH*HCl. Anhydrous ethanol(EtOH) is used for extraction of the Hydroxylammonium chloride, the KCl remains undissolved. The EtOH is evaporated on a water bath and the product can be recrystallised from water (mp 151°C).

A similar method can be found in Organic Synthesis.

Ref: Jander-Blasius, Lehrbuch der anal. u. prep. anorg. Chemie