Check the listing for details. Antique Copper Brewery Proof Hydrometer. Not Tested.. Listed at 80.00 USD. The Antique Copper Brewery Proof Hydrometer from 1943 is an original piece that has not been tested. This unique scientific instrument would have been used for measuring the specific gravity of liquids in the brewing process. With a rich history and craftsmanship, this item would make a valuable addition to any antique science equipment collection. Not tested. Missing top