A mixture of KNCS and KHSO4 is ground together as finely as
possible and allowed to stand for 3-4 weeks over P3OS. Then
flask a of an apparatus is successively charged (the order of addition should be maintained)
with 250 g. of glass beads (6-7 mm. in diameter), 100 g. of KNCS
alternated with beads, then a covering layer of glass beads, then
the required amount of KHSO4 mixed with glass beads. Without
disturbing these layers, the glass flask is mounted in a rigid
support and joined on one side of the horizontal tube p via a ground
glass spray trap / . The other ground glass joint of a is closed off
with a cap. KNCS + KHSO4 = K2SO4 + HNCS