Abstract
In the thiocholine method of Koelle as previously described (17), the enzymatic reaction step leads to the formation of crystalline deposits. These have been identified as Cu·thiocholine sulfate. The subsequent ammonium sulfide treatment aiming at the conversion of Cu·thiocholine to CuS implies that the previous crystals become dissolved and replaced by amorphous precipitates. The environmental and other operating factors in this multi-step method are discussed.