Carbon Residue of Oils

These methods provide  some  indication of the  coke forming tendencies  of oils and  hence have  little  application  to gear  lubricants. Also oils  containing ash – forming  ingredients will have  erroneously  high  carbon residue. Values  obtained by  the  two  methods  noted  are not the same. Older  specifications for high  viscosity oils  often  give the Carbon  Residue by the Conradson Method, but the present thought is to  use the  Ramsbottom  Method

For the determination  of this  value a weighed  amount of oil is  subjected to heat so that  evaporation and  pyrolysis  takes  places under  conditions of  restricted  air  supply. In  fact  in the Ramsbottom  Method the  sample  is contained  in  a Coking  Bulb with  a very small  opening. While  the term  Carbon  Residue  is used, it is  recognized  that the  coke  remaining  after  such  tests is not  entirely  composed of carbon.