Preparation of cobalt thiosulfate
To a solution of 70.0 g of cobalt(II) sulfate heptahydrate in 200 ml of water warmed to 50° C are added 67.0 g of barium thiosulfate monohydrate. The mixture is stirred at 50° C until the barium sulfate settles out completely and it is then filtered. Acetone (about 500 ml) is now added to the clear filtrate in a one-liter beaker until the deposition of a reddish oil is complete and the supernatant liquid is almost colorless. The oil is repeatedly stirred with fresh 75-100 ml portions of acetone until it starts to solidify, whereupon it is transferred to a large mortar and further triturated with acetone until it is thoroughly granular. The reddish-brown residue is collected on a filter and dried in air yielding 45 g of cobalt thiosulfate. Cobalt thiosulfate obtained by described method contains cobalt sulfate.
Inorganic laboratory preparations, by G. G. Schlessinger, 45, 1962