Probably a sacrificial anode. The carbon would be oxidized to carbon dioxide before the copper would be oxidized.
From the document
Make a mixture of Wood Coal Powder Salt & Sand all in equal part
Wood Coal Powder use as good conductor of electricity, anti corrosive, rust proves for GI Plate for long life.
The purpose of coal and salt is to keep wet the soil permanently.
The salt percolates and coal absorbs water keeping the soil wet.
Care should always be taken by watering the earth pits in summer so that the pit soil will be wet.Coal is made of carbon which is good conductor minimizing the earth resistant.
Salt use as electrolyte to form conductivity between GI Plate Coal and Earth with humidity.
Sand has used to form porosity to cycle water & humidity around the mixture.
Well, It's August. I must go water my ground pit. I don't think that will happen in most cases.
