Purified Copper Sulphate: Iron Thrown Down by Fresh Copper Carbonate, Then Recrystallised

Ordinary copper sulphate usually carries a little iron sulphate. The 1907 US Dispensatory gives the cure: add freshly precipitated copper carbonate, which throws the iron down as carbonate, then filter and crystallise. The pharmacopoeia salt had to be at least 99.5 % pure copper sulphate. Making the copper carbonate from part of the same solution, and drying below 30 °C, are our choices. The source gives no quantities, so none are given here. The picture: a copper sulphate crystal (Crystal Titan, Wikimedia Commons, CC BY-SA 4.0).