Until 2001, all Ritchie compasses (see exception) were filled with Odorless Mineral Spirits (100% Paraffin based). Ritchie now uses a fluid called Isopar L that has similar properties but some added benefits over Odorless Mineral Spirits.
Exception: Some old style Flat Top Compasses used a mix of denatured alcohol and water. This process was stopped in the 1960s. If you have a Flat Top Compass, it is recommended that you test the fluid to see if it is Odorless Mineral Spirits or an alcohol/water mix.