During cold winter weather: seal hives to keep steam, usually with foam barrels at the entrance.Add the correct amount of oxalic acid (as detailed in the container) to the cup of the evaporator.Connect to the 12V car battery and place the evaporator cup into the center of the hive through the entrance.Seal the entrance.Leave until all oxalic acid has evaporated (a few minutes) and removed.Seal for a few more minutes, then remove the foam plug from the entrance.