removal of magnetic coatings from computer memory discs is achieved by immersing the discs in a bath of a sulphuric - acid and glycerine solution while applying an electrical potential between electrodes in the bath , one of which is the disc itself . after removal of the disc from the sulphuric - acid glycerine solution , it is sequentially immersed in alcohol and then water ; any remaining coating is next mechanically removed and then the disc is immersed in high purity water and dried .